1. An AC motor Control unit (24) comprising: a power converter (20) for converting a supplied electric power into an electric power of variable voltage and variable frequency and driving an AC motor (30) at a variable speed; a PWM (pulse width modulation) control unit (45) for controlling the power converting function of the power converter (20); and a current detection unit abnormality decision device (48) having command voltage calculating means (47) used for decision on abnormality and outputting a command voltage signal for making a decision as to whether there is any abnormality in a current detection unit (50) operating to detect electrical currents flowing through the AC motor (30) and abnormality decision means (46) for making a decision as to whether there is abnormality in the current detection unit (50), depending on a pattern of electrical currents obtained from the current detection unit (50) by applying the command voltage signal to the power converter (20) for driving the motor; wherein the PWM control unit (45) supplies a control signal (43S) to the power converter (20) for driving the motor (30), based on an external command signal (45S) and on detection signals (5IS, 52S) from the current detection unit (50); and wherein, when the current detection unit abnormality decision device (48) determines that there is abnormality in the current detection unit (50) prior to operation of the AC motor (30), the AC motor Control unit provides an output for displaying abnormality.

2. An AC motor Control unit (24) comprising: a power converter (20) for converting a supplied electric power into an electric power of variable voltage and variable frequency and driving an AC motor (30) at a variable speed; a PWM control unit (45) for controlling the power converting fiinction of the power converter (20) for driving the motor (30); and a current detection unit abnormality decision device (48) having command voltage calculating means (47) used for decision on abnormality and outputting a command voltage signal to make a decision as to whether there is any abnormality in a current detection unit (50) operating to detect electrical currents flowing through the AC motor (30) and abnormality decision means (46) for making a decision as to whether there is any abnormality in the current detection unit (50) depending on a pattern of electrical currents obtained from the current detection unit (50) by applying the command vohage signal to the power converter (20) W6882 -34- for driving the motor; wherein said PWM control unit (45) supplies a control signal (43 S) to the power converter (20) for driving the motor, based on the external command signal (45S) and on detection signals (5IS, 52S) from the current detection unit (50); wherein said command voltage calculating means (47) used for abnormality decision supplies the voltage command signal plural times to the power converter (20) for driving the motor while varying the phase of the voltage command signal; and wherein said abnormality decision means (46) compares a detection current pattern assumed from a pattern of the voltage command signals applied in turn with the detection signals (5 IS, 52S) from the current detection unit (50) and, if the detection current pattern does not agree with the assumed detection current pattern, determines that the current detection unit (50) is misconnected and issues a warning.

3. The AC motor Control unit (24) according to claim 1 or 2, wherein said current detection unit abnormality decision device (48) is configured including a command voltage calculator (47) used for decision on abnormality and operating to calculate a first-order angular frequency command, a d-axis command voltage, and a q-axis command vohage and an abnormality decision device (46) for comparing detection currents of various phases from the current detection unit (50), performing calculations, and making a decision as to whether there is any abnormality.

4. The AC motor Control unit (24) according to claim 1 or 2, wherein said PWM control unit (45) is configured including: a three-phase AC current coordinate converter (44) for converting detection currents of various phases entered from the current detection unit (50) into a d-axis current and a q-axis current; a vector control unit (41) for calculating a d-axis command voltage and a q-axis command voltage for the AC motor (30) based on information about the d-axis current and the qaxis current delivered from the three-phase AC current coordinate converter (44); a three-phase AC voltage coordinate converter (42) for converting the d-axis command voltage and the q-axis command voltage delivered from the vector control unit (41) into a three-phase AC command voltage; and a pulse generation unit (43) for converting the three-phase AC command voltage into a PWM control signal.

5. The AC motor Control unit (24) according to claim 1 or 2, wherein some or all of fiinctions of said AC motor Control unit (24) are implemented by computer programs. W6882 -35-

6. A method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) which comprises: power conversion means (20) for converting a supplied electric power into an electric power of variable voltage and variable frequency and driving an AC motor (30) at a variable speed; PWM control means (45) for controlling the power converting ftmction of the power conversion means (20) for driving the motor; and current detection unit abnormality decision means (48) having a command voltage calculating fiinction used for abnormality decision and for outputting a command voltage signal to make a decision as to whether there is any abnormality in the current detection unit (50) operating to detect currents flowing through the AC motor (30) and an abnormality deciding fiinction of making a decision as to whether there is any abnormality in the current detection unit (50) depending on a pattern of electrical currents obtained from the current detection unit (50) by applying the command voltage signal to the power conversion means (20) for driving the motor; said method comprising the steps of supplying a control signal from the PWM control means (45) to the power conversion means (20) for driving the motor, based on an external command signal (45 S) and on detection signals (5IS, 52S) from the current detection unit (50); and causing the current detection unit abnormality decision means (48) to provide an output for displaying abnormality when the decision means (48) determines that there is abnormality before the AC motor (30) is run.

7. A method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) according to claim 6, wherein said current detection unit abnormality decision means (48) provides a command vohage signal to apply plural voltages to various phases of the AC motor (30) before the AC motor (30) is run.

8. The method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) according to claim 7, wherein when said current detection unit abnormality decision means (48) applies the command voltage signal of a DC vohage plural times while varying its magnitude, if values that are substantially identical within a given range of levels are detected, the current detection unit abnormality decision means (48) determines that the current detection unit (50) is damaged or misconnected and causes the AC motor Control unit (24) to output a warning of abnormality in the current detection unit (50).

9. The method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) according to claim 8, wherein when the warning of W6882 -36- abnormality in the current detection unit (50) is outputted, said current detection unit abnormality decision means (48) determines that there is an error caused by non-connection of the current detection unit (50), a damage to the current detection unit (50), or wire breakage.

10. The method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) according to claim 9, wherein when said current detection unit abnormality decision means (48) applies the command voltage signal of a DC voltage plural times while varying its magnitude, if a variation more than a given level is detected in response to the applied vohage and if the ratio of output signals from two current detection units (51, 52) of the current detection unit (50) agrees with none of three patterns which are respectively delineated by < 1 > ± 2 times, < 2 > ± 1/2 times, and < 3 > + 1 times within a given range of levels, the current detection unit abnormality decision means (48) determines that there is damage to the current detection unit (50) and causes the AC motor Control unit (24) to output a warning of abnormality in the current detection unit (50).

11. A method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) which comprises: power conversion means (20) for converting a supplied electric power into an electric power of variable voltage and variable frequency and driving an AC motor (30) at a variable speed; PWM control means (45) for controlling the power converting function of the power conversion means (20) for driving the motor; and current detection unit abnormality decision means (48) having command vohage calculating means (47) used for decision on abnormality and for outputting a command voltage signal to make a decision as to whether there is any abnormality in the current detection unit (50) operating to detect currents flowing through the AC motor (30) and abnormality decision means (46) for making a decision as to whether there is any abnormality in the current detection unit (50) depending on a pattern of electrical currents obtained from the current detection unit (50) by applying the command voltage signal to the power conversion means (20) for driving the motor; said method comprising the steps of supplying a control signal to said motor-driving power conversion means (20) from said PWM control means (45) based on an external command signal (45 S) and on detection signals (5IS, 52S) from said current detection unit (50); supplying said command voltage signal plural times to said power conversion means (20) for driving the motor while varying its phase from said command voltage calculating means (47) for abnormality decision; - 3 7 - comparing a detection current pattern assumed from a pattern of the command signal applied plural times with detection signals delivered from the current detection unit (50) by said abnormality decision means (48); and determining that said current detection unit (50) is misconnected and causing the AC motor Control unit (24) to output a warning of abnormality in the current detection unit (50) if no coincidence takes place with the assumed detection current pattern.

12. A method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) according to claim 11, wherein when said current detection unit abnormality decision means (48) applies a DC voltage plural times to said power conversion means (20) for driving the motor while varying the magnitude of the DC voltage, the current detection unit abnormality decision means (48) classifies misconnections of the current detection unit (50), depending on the ratio of output signals from two current detection units (51, 52) of the current detection unit (50) and on phases set on application of the command signal.

13. The method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) according to claim 12, wherein said current detection unit abnormality decision means (48) detects misconnections of the current detection unit (50) according to results of the classification of misconnections of the current detection unit (50).

14. The method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) according to claim 12 or 13, wherein when a misconnection is detected, said current detection unit abnormality decision means (48) judges a pattern of detection currents created by the detected misconnection, based on results of the classification of misconnections of the current detection unit (50) made depending on the ratio of output signals from two detection units (51, 52) of the current detection unit (50) and on phases set on application of the command signal.

15. A method of checking soundness of a current detection unit (50) for use in or with an AC motor Control unit (24) according to claim 14, wherein said current detection unit abnormality decision means (48) outputs a preset connection modifying pattern in response to a pattern of detection currents created by the detected misconnection.

16. An AC motor Control unit, substantially as herein described with reference to accompanying drawings and examples.

17. A method of checking soundness of a current detection unit, substantially as herein described with reference to accompanying drawings and examples.

W6882
1-
BACKGROUND OF THE INVENTION
The present invention relates to an Alternating Current (AC) motor control unit
for driving and controlling an AC motor and also to a method of checking the soundness of a
current detection unit (i.e., whether there is any abnormality in the detector) used to control the
5 AC motor Control unit.
When the operation of an AC motor is controlled using a power converter, a
control loop is used to provide voltage adjustment such that a current value obtained by detecting
an electrical current flowing through a winding in the AC motor by the use of a current detection
unit agrees with the command current computed within the AC motor Control unit. However, if
10 the current detection unit is not yet connected or misconnected, there is the possibility that the
overcurrent protection does not fimction but the power converter itself is damaged although an
excessive current is flowing in practice.
A technique for offering a countermeasure against this problem is disclosed, for
example, in patent literature 1 (JP-A-2010-183698). In particular, a decision is made as to
15 whether the current detection unit is connected correctly or incorrectly using a current value
obtained when the detector is energized with a DC current. In this way, it is determined
whether the detector is not connected or misconnected.
In the prior art including the technique disclosed in patent literature 1, however,
the function of detecting only abnormality in the connection of a current detection unit is used as
20 described previously. There is the problem that it is difficult to judge abnormality in the current
detection unit in a case where the current detection unit is connected normally but the output
signal is in an inappropriate state due to damage to the detector itself
Furthermore, when the current detection unit itself has no problem and the
connection of the detector is not problematic, if an AC motor connected with an AC motor
25 Control unit has a large internal resistance value, the produced current is small. Therefore, the
current detected by the current detection unit is also small. In this case, there is the possibility
that the current detection unit will be incorrectly judged to be not yet connected.
Another problem is that it is diflficuh to discriminate a current detection unit
connected normally with output terminals of a power converter from a misconnected current
30 detection unit.
W6882
- 2 -
SUMMARY OF THE INVENTION
In view of the foregoing problems, the present invention has been made. It is an
object of the invention to provide an AC motor Control unit permitting one to previously check
whether a current detection unit is connected normally with the output terminals of a power
5 converter for driving an electric motor
This object is achieved in accordance with the teachings of the present invention
by an AC motor Control unit having: a power converter for converting a supplied electric power
into an electric power of variable vohage and variable frequency and driving an AC motor at a
variable speed; a PWM (pulse width modulation) control unit for controlling the power
10 converting fiinction of the power converter; and a current detection unit abnormality decision
device. This abnormality decision device has command voltage calculating means used for
decision on abnormality and outputting a command voltage signal for making a decision as to
whether there is any abnormality in a current detection unit, the current detection unit operating
to detect electrical currents flowing through the AC motor. Furthermore, the decision device
15 has abnormality decision means for making a decision as to whether there is abnormality in the
current detection unit, depending on a pattern of electrical currents obtained from the current
detection unit by applying the command voltage signal to the power converter for driving the
motor. The PWM control unit supplies a control signal to the power converter for driving the
motor, based on an external command signal and on detection signals from the current detection
20 unit. When the current detection unit abnormality decision device determines that there is
abnormality in the current detection unit prior to operation of the AC motor, the AC motor
Control unit provides an output for displaying abnormality.
Other means will be set forth in the description of the aspects for carrying out the
present invention.
25 As described so far, the present invention can offer an AC motor Control unit and
method capable of previously checking whether a current detection unit is connected normally
with the output terminals of a power converter.
BRIEF DESCRIPTION OF THE DRAWINGS
30 FIG. 1 is an electrical circuit diagram showing one example of configuration of an
AC motor Control unit associated with a first embodiment of the present invention, as well as
structural relations among the AC motor Control unit, an AC source, a current detection unit, and
an AC motor
FIG. 2 is a flowchart illustrating a current detection unit abnormality decision
W6882
- 3 -
mode executed by a command voltage calculator for making a decision whether there is
abnormality in the current detection unit in the AC motor Control unit associated with the first
embodiment of the invention.
FIG. 3 A is a diagram showing the relations among vectors in a case where
5 measuring voltages Vdl, Vd2, and Vd3 are applied to a d-axis command voltage Vdref by the
AC motor Control unit associated with the first embodiment of the invention under the condition
where d-axis and u-phase are made coincident in phase relationship, as well as the relation
between u-phase detection current lu and w-phase detection current Iw.
FIG. 3B is a diagram showing vector relations among u-phase, v-phase, and w-
10 phase and a vector relation between u-phase detection current lu and w-phase detection current
Iw.
FIG. 3C is a graph showing the association among d-axis command voltage Vd, uphase
detection current lu, and w-phase detection current Iw.
FIG. 3D shows a mathematical formula about u-phase detection current lu and w-
15 phase detection current Iw when the current detection unit is in a normal state.
FIG. 4A is a diagram illustrating a second control method by which the AC motor
Control unit associated with the first embodiment of the invention applies d-axis command
vohage Vd under the condition where 0d = 0.
FIG. 4B is a diagram similar to FIG. 4A, but in which d-axis command voltage Vd
20 is applied under the condition where 9d = 27i/3.
FIG. 4C is a diagram similar to FIG. 4A, but in which d-axis command voltage Vd
is applied under the condition where 0d = 47r/3.
FIG. 5 A shows a normal connective relation between the power converter and
current detection unit of the AC motor Control unit associated with the first embodiment of the
25 invention.
FIG. 5B shows an example of a misconnected relation between the power
converter and the current detection unit.
FIG. 6A is a diagram illustrating the relation between lu and Iw in cases where
terminals of a power converter of an AC motor Control unit associated with a second
30 embodiment of the present invention and a current detection unit are normally connected
together and where the phase difference 6d between u-axis and d-axis is varied to 0 (6d = 0)
under a second set of measuring conditions.
FIG. 6B is a diagram similar to FIG. 6A, but in which 6d = 27t/3.
FIG. 6C is a diagram similar to FIG. 6A, but in which 0d = 4ii/3.
W6882
- 4 -
FIG. 7A is a diagram illustrating the relation between lu and Iv in cases where
terminals of the power converter of the AC motor Control unit associated with the second
embodiment of the present invention and the current detection unit are normally connected
together and where the phase difference 9d between u-axis and d-axis is varied to 0 (9d = 0)
5 under the second set of measuring conditions.
FIG. 7B is a diagram similar to FIG. 7A, but in which 9d = 2nl3.
FIG. 7C is a diagram similar to FIG. 7A, but in which 9d == 47i/3.
FIG. 8 is a table showing the relations among detection currents lu, Iv, and Iw
from the current detection unit when single-phase DC excitation is done while modifying the
10 connection positions of the current detection unit and the phase difference 9d about u-, v-, and
w-phases from the output terminals of the AC motor Control unit associated with the second
embodiment of the invention.
FIG. 9 is a flowchart illustrating a method for making a decision as to whether the
AC motor Control unit associated with the second embodiment of the invention is correctly
15 connected with the current detection unit, forjudging a misconnected current detection unit and
phases with which this current detection unit is connected during measurement, and for
displaying normal connection destinations.
FIG. 10 is a table showing pattern matching illustrating the correspondence
between combinations of mathematical formulas about detection currents from the current
20 detection unit and the AC motor Control unit associated with the second embodiment of the
invention and the connective state of the current detection unit.
FIG. 11 is a table showing the correspondence among the state of connection of
the current detection unit with the AC motor Control unit associated with the second
embodiment of the invention judged by pattern matching of detection currents from the current
25 detection unit, a misconnected current detection unit, and phases with which this current
detection unit is connected.
FIG. 12 is a table showing the correspondence among the state of connection of
the current detection unit with the AC motor Control unit associated with the second
embodiment of the invention judged by pattern matching, a misconnected current detection unit,
30 and normal connection destinations of the current detection unit.
DESCRIPTION OF THE EMBODIMENTS
The preferred embodiments of the present invention are hereinafter described
with reference to the drawings.
W6882
- 5 -
(First Embodiment)
One example of configuration of an AC motor Control unit is described as a first
embodiment of the present invention. The following description centers on the configuration
and fiinctions of the control unit, but methods are also explained.
5 FIG. 1 shows one example of configuration of the AC motor Control unit,
indicated by reference numeral 24, associated with the first embodiment of the present invention.
Also, an example of relations among the AC motor Control unit 24, an AC source 10, a current
detection unit 50, and an AC motor 30 is shown.
[Overall Configuration]
10 In FIG. 1, the AC motor Control unit 24 (substantially, a power converter 20
incorporated in the AC motor Control unit 24) to which a three-phase AC power is supplied from
the AC source 10 converts the power into a desired three-phase AC power of variable voltage
and variable frequency based on instructions given by an external command signal 45S, and
outputs the power. The AC motor 30 is driven at a variable speed by the outputted three-phase
15 AC power.
The current detection unit 50 is installed in three-phase wiring that connects the
power converter 20 of the AC motor Control unit 24 with the AC motor 30. The converter 20
forms a power converter or power conversion means for driving the electric motor. The AC
motor Control unit 24 controls and drives the AC motor 30 while referring to the current value
20 detected by the current detection unit 50 and to instructions given by the external command
signal 45 S.
As an example, the current detection unit 50 consists of two detection units, i.e., a
u-phase current detection unit 51 for detecting u-phase and a w-phase detection unit 52 for
detecting w-phase, for the following reason. In the case of a three-phase alternating current, the
25 vector sum of u-phase, v-phase, and w-phase is equal to 0. Therefore, if the u-phase and wphase
are detected, the remaining v-phase can be found by a calculation. Hence, three current
detection units are not required.
The AC motor Control unit 24 has a function of detecting abnormality in the
current detection unit 50 including the detection units 51 and 52. Details of this flmction will
30 be described later.
[Configuration of AC motor Control unit 24]
The AC motor Control unit 24 is configured including the power converter 20 and
a power converter unit control apparatus 40.
The power converter 20 has rectifiers or converters (not shown) and a PWM
W6882
- 6 -
(pulse width modulation) inverter (not shown). The three-phase AC power from the AC source
10 is once converted into a DC power by the rectifiers or converters. Using the DC power as a
power source, the PWM inverter converts the power into a three-phase AC power of variable
voltage and variable frequency. The three-phase power is supplied to the AC motor 30 as
5 mentioned previously.
The power converter unit control apparatus 40 controls the conversion operation
of the power converter 20. Details of the power converter unit control apparatus 40 are next
described.
< Configuration and Operation of Power converter unit Control apparatus 40 >
10 The power converter unit control apparatus 40 is configured including a PWM
control unit 45, a current detection unit abnormality decision device 48, and a switch 49. When
the AC motor 30 is run, a PWM signal is sent to the power converter 20 from the PWM control
unit 45 to controllably drive the motor 30 at a variable speed.
When abnormality (fault or misconnection of wire) in the current detection unit
15 50 is detected or judged prior to operation of the AC motor 30, the current detection unit
abnormality decision device 48 is operated. The measured signal is fed to the power converter
20. A u-phase detection current lu and a w-phase detection current Iw from the current
detection unit 50 are entered to the current detection unit abnormality decision device 48, where
a decision is made.
20 The used signal is switched between the signal from the PWM control unit 45 and
the signal from the current detection unit abnormality decision device 48 by the switch 49,
depending on the current mode of operation. Details of the PWM control unit 45 and current
detection unit abnormality decision device 48 will be described later. The PWM control unit 45
is first described.
25 « Configuration and Operation of PWM control unit 45 »
The PWM control unit 45 is configured including a vector control unit 41, a threephase
AC voltage coordinate converter 42, a three-phase AC current coordinate converter 44, and
a pulse generation unit 43.
The three-phase AC current coordinate converter 44 for the d- and q-axes
30 converts the u-phase detection current lu (51S) and the w-phase detection current Iw (52S)
entered from the current detection unit 50 into a d-axis current Id and a q-axis current Iq,
respectively, based on a first-order angular frequency command colref (49S) and outputs them.
Information about these d-axis current Id and q-axis current Iq is entered to the vector control
unit 41.
W6882
The vector control unit 41 computes a d-axis command voltage Vdref, a q-axis
command voltage Vqref, and the first-order angular frequency command co Iref for the AC motor
30 for controlling the output torque and speed of the AC motor 30 so as to satisfy desired
characteristics, based on information about the d-axis current Id and q-axis current Iq obtained
5 from the external command signal 45 S and three-phase AC current coordinate converter 44, and
outputs them.
The three-phase AC voltage coordinate converter 42 for the d- and q-axes
converts the d-axis command voltage Vdref and q-axis command voltage Vqref delivered from
the vector control unit 41 into a three-phase command AC voltage 42S based on the first-order
10 angular frequency instruction colref
The d-axis command voltage Vdref may be abbreviated as the "d-axis command
voltage Vd". The switch 49 is located between the vector control unit 41 and the three-phase
AC voltage coordinate converter 42. In this configuration, it is assumed that first to third
switching elements of the switch 49 are connected to termcinals Sdl, Sql, and Sol, respectively,
15 of the switch.
Where the AC motor 30 is a synchronous motor, the d-axis is the center axis of
the field pole. Where the motor is an induction motor, the d-axis lies in the direction of the
main magnetic flux. In FIGS. 3 A and 3B, the q-axis is electrically perpendicular to the d-axis.
The pulse generation unit 43 converts the three-phase command AC voltage 42S
20 into a PWM control signal 43 S for pulse width control and outputs the command voltage. The
PWM control signal 43 S is applied to the power converter 20. Because of the configuration
and operation described so far, the PWM control unit 45 outputs the PWM control signal to turn
on and oflFthe switching device of the power converter 20 to control the power converter 20 such
that the output voltage from the power converter 20 agrees with the command voltage value
25 indicated by the external command signal 45 S.
« Current detection unit Abnormality Decision Device 48 »
The current detection unit abnormality decision device 48 is configured including
an abnormality decision device 46 (which forms abnormality decision means and has a function
of making a decision as to whether there is abnormality) and a command voltage calculator 47
30 used for decisions made whether there is any abnormality. The calculator 47 forms a command
vokage calculating means for decisions made as to whether there is any abnormality, and has a
function of calculating a command voltage used for decisions made as to whether there is any
abnormality.
The abnormality decision device 46 enters the u-phase detection current lu (5IS)
W6882
- 8 -
and the w-phase detection current Iw (52S) from the current detection unit 50 and makes a
decision as to whether the current detection unit 50 or associated state is abnormal or normal.
The command voltage calculator 47 used for decisions made as to whether there
is any abnormality is configured including measuring signal generating means for outputting the
5 first-order angular frequency command co Iref, d-axis command voltage Vdref, and q-axis
command voltage Vqref such that a given voltage is applied to the AC motor 30 using the power
converter 20 in a current detection unit abnormality decision mode in which any abnormality in
the current detection unit 50 is detected or judged.
Decision method and method of calculations adopted by the abnormality decision
10 device 46 and command voltage calculator 47 used for decisions made as to whether there is any
abnormality will be described in detail later.
« Switch 49 »
The switch 49 has the first to third switching elements Sd, Sq, and So,
respectively. Using these switching elements, the used signal is switched between the case
15 where the AC motor 30 is driven and run and the case where the current detection unit
abnormality decision mode is executed. That is, where the AC motor 30 is driven and run, the
first to third switching elements Sd, Sq, and So are connected to the terminals Sdl, Sql, and
Scol, respectively. The d-axis command voltage Vdref, q-axis command voltage Vqref, and
first-order angular frequency command a Iref from the vector control unit 41 are transferred to
20 the three-phase AC voltage coordinate converter 42.
In the current detection unit abnormality decision mode, the three switching
elements Sd, Sq, and So are connected to the terminals Sd2, Sq2, and Sal, respectively. The
vector control unit 41 is disconnected. The measuring conditions (Vdref, Vqref, and co Iref)
under which abnormality of the current detection unit of the command voltage calculator 47 for
25 abnormality decision is detected are transferred to the three-phase AC voltage coordinate
converter 42. Details of the measuring conditions will be described later.
« First Control Method regarding Current detection unit Abnormality Decision Mode »
A first control method implemented by the abnormality decision device 46 of the
current detection unit that is a main constituent of the present invention to make a decision as to
30 whether there is any abnormality in the current detection unit 50 is next described.
This decision on abnormality is made before the AC motor 30 is run, in order to
check whether there is abnormality in the current detection unit 50 connected with the wiring in
the AC motor 30. Therefore, when the AC motor and the current detection unit are newly
W6882
- 9 -
arranged, the current detection unit is replaced, or the current detection unit is serviced routinely,
tests are performed in the current detection unit abnormality decision mode while the AC motor
30 is stopped. Thus, a decision is made as to whether there is any abnormality.
In the following description, it is assumed that the current detection unit 50 is
5 connected with two of the three output terminals u, v, and w of the power converter 20.
< Flowchart for Current detection unit Abnormality Decision Mode (First Control Method) >
FIG. 2 is a flowchart illustrating the current detection unit abnormality decision
mode executed by the command voltage calculator 47 to make a decision as to whether there is
any abnormality in the current detection unit 50 under control of the AC motor Control unit 24
10 associated with the first embodiment of the present invention. The processing steps of the
method for making a decision as to whether there is abnormality are described in turn with
reference to the flowchart of FIG 2.
« Step S21 »
Step S21 is performed to enter rated voltage VI and rated current II, i.e.,
15 nameplate information about the motor (setting forth rated power capacity, rated voltage, rated
current, rated rotational speed, number of poles, and so forth). These pieces of information are
used as a reference for a set range of measured voltages and current values derived fi'om the
current detection unit in an abnormality detection mode (described later). In FIG. 2, the step
S21 is stated as "Input of nameplate information: rated voltage and rated current".
20 «Step S22 »
Step S22 is performed to output and apply a command voltage for detecting
whether there is any abnormality in the current detection unit 50 (FIG. 1). In particular, the
switching elements Sd, Sq, and S® of the switch 49 (FIG. 1) are brought to terminals Sd2, Sq2,
and Sco2, respectively. The vector control unit 41 is disconnected. The measuring conditions
25 (first set of measuring conditions (hereinafter may be abbreviated as condition 1)) under which
the command voltage calculator 47 for abnormality decision detects abnormality in the current
detection unit are transferred to the three-phase AC voltage coordinate converter 42.
The first set of measuring conditions is that: first-order angular fi-equency
command colref = 0, phase difference 0d between u-phase and d-axis = 0, and q-axis command
30 voltage Vqref = 0. Plural measuring voltages (Vmodell(l), Vmodell(2), and Vmodell(3)) are
given to the d-axis command voHage Vdref
CO Iref = 0 means that the current is a DC current. 0d (phase difference) = 0
means that the u-phase and the d-axis are coincident in direction. Vqref = 0 means that a
voltage is applied only in the direction of the d-axis. The measuring voltages Vmodell(l),
W6882
-10-
Vmodell(2), and Vmodell(3) may be hereinafter abbreviated as Vdl, Vd2, and Vd3,
respectively.
The different measuring vohages (Vdl, Vd2, and Vd3) are applied in turn for the
following reason. Where the output from the motor connected with the power converter 20 is
5 small, if the internal resistance value of the motor is large and the applied voltage is low (such as
when Vdl is applied), the detected current value is small even if the current detection unit is in a
normal state and connected correctly. In this case, it is impossible to make a precise decision.
Accordingly, plural voltages of different magnitudes are applied in turn, and decisions are made
based on Equations (Eqs.) (1) and (2) described later.
10 A command vohage for doing single-phase DC excitation under this first set of
measuring conditions is outputted. The measuring voltage is applied to the AC motor 30 by the
power converter 20 via both three-phase AC voltage coordinate converter 42 and pulse
generation unit 43. In FIG. 2, this step S22 is stated as "Abnormal detection mode 1: singlephase
DC excitation, condition 1".
15 « Step S23 »
Step S23 is used to detect the u-phase current and the w-phase current delivered
from the power converter 20 of the current detection unit 50 under the measuring conditions of
step S22. In FIG. 2, this step S23 is stated as "Detection of u-phase current and w-phase
current".
20 « Step S24 »
Step S24 is used to make a decision as to whether the u-phase detection currents
lul, Iu2, and Iu3 and w-phase detection currents Iwl, Iw2, and Iw3 vary in value when the
currents are detected while applying the plural measuring voltages Vdl, Vd2, and Vd3 to the daxis
command voltage Vd (Vref) in turn.
25 Specifically, if the u-phase detection currents lul, Iu2, and Iu3 or w-phase
detection currents Iwl, Iw2, and Iw3 vary little in value (Yes at step S24) in spite of the fact that
the measuring voltage is varied from Vdl to Vd2 and then to Vd2 during measurements, control
goes to step S27. If the u-phase detection currents lul, Iu2, and Iu3 and w-phase detection
currents Iwl, Iw2, and Iw3 vary in value (No at step S24) while varying the measuring voltage
30 from Vdl to Vd2 and then to Vd3, control proceeds to step S25. In FIG. 2, this step S24 is
stated as "No variations in detection signals?"
« Step S25 »
This step S25 is used to make a decision as to whether given formulas still hold in
spite of the fact that the measuring voltage is varied in value, the formulas interrelating the uW6882
- 11-
phase detection currents lul, Iu2, and Iu3 and the w-phase detection currents Iwl, Iw2, and Iw3
which are obtained when the currents are detected while giving the plural values of the
measuring vohage of Vdl, Vd2, and Vd3 to the d-axis command voltage Vd in turn.
Under normal conditions, the u-phase detection currents lul, Iu2, and Iu3
5 detected at the u-phase and the w-phase detection currents Iwl, Iw2, and Iw3 detected at the wphase
are represented by the following equation set (1).
Iul=-2xlwl, Iu2 = -2xlw2, Iu3 = - 2 x Iw3 (1)
10 The reason why the equation set (1) is obtained will be described later.
In step S25, if the normal relations among the detection signals, i.e., equation set
(1), hold among the u-phase detection currents lul, Iu2, and Iu3 and the w-phase detection
currents Iwl, Iw2, and Iw3 (Yes at step S25), then control goes to step S26.
In step S25, if the normal relations among the detection signals (equation set (1))
15 do not hold (No at S25), then control goes to step S28. In FIG. 2, this step S25 is stated as
"normal relations among detection signals?"
« Step S26 »
Step S26 is used to display a word "normal" or the equivalent indicating that the
current detection unit is in a normal state. That is, reaching step S26 means that the current
20 detection unit is in a normal state and that the wires are connected normally. Furthermore, it is
meant that connections at connection locations are good. Therefore, the result of the decision is
normal, which is displayed.
At the stage when the "normal" state is displayed, controls goes to "END", thus
terminating this subroutine for a decision made as to whether or not the current detection unit is
25 abnormal. In FIG. 2, this step S26 is stated as ""normal" state of current detection unit is
displayed".
« Step S27 »
Step S27 is performed when the decision at step S24 is Yes, i.e., no variations in
the detection signals. That is, the u-phase detection currents lul, Iu2, and Iu3, i.e., detection
30 signals, are below a given level although measurements are made while varying the measuring
vohage from Vdl to Vd2 and then to Vd3. It is considered that the cable of the power
converter is not yet connected with the AC motor or that the detection signals are not delivered
from the current detection unit to the AC motor Control unit. Accordingly, it is meant that the
current detection units 51 and 52 themselves are damaged or that connections are not completed
W6882
-12-
or wire breakage occurs.
As such, in step S27, an error display is provided, meaning that there is a wire
breakage error or there is damage to the current detection unit. At the stage when "wire
breakage error or current detection unit damage error" is displayed, control goes to "END", thus
5 terminating this subroutine for making a decision as to whether there is any abnormality in the
current detection unit. In FIG. 2, this step S27 is stated as "wire breakage error or current
detection unit damage error is displayed".
« Step S28 »
Step S28 is performed when the decision at step S25 is No (i.e., the relations
10 among the detection signals are not normal). It is assumed that equation set (1) does not hold
but there are relationships given by equation set (2).
Iul;t-2xlwl, Iu2?^-2xlw2, Iu3;t-2xlw3 (2)
15 For example, where the current detection unit 51 detecting the u-phase current is
abnormal, the current lu (lul, Iu2, Iu3) detected at the u-phase provides outputs of abnormal
values.
Therefore, when a decision is made using the abnormal decision device 46 for the
current detection unit, equation set (2) holds. In step 828, it is assumed that there are relations
20 given by equation set (2) and so the current detection units 51 or 52 is taken as abnormal, and a
damage error display for the current detection unit is provided. If there is a wire breakage
rather than current detection unit damage, control proceeds to step S27. At the stage when
"current detection unit damage error" is displayed, control goes to "END", thus terminating this
subroutine for making a decision as to whether there is any abnormality in the current detection
25 unit. In FIG. 2, this step S27 is stated as "current detection unit damage error is displayed".
As described so far, before the AC motor is run, abnormality in the current
detection unit can be detected by applying an abnormality decision signal for the current
detection unit 50 to the AC motor 30 from the power converter 20 and analyzing the resulting
values of the currents detected by the current detection unit 50. Consequently, extensive
30 damage to the AC motor Control unit 24 and to the AC motor 30 can be prevented.
< Relations between Voltages and Currents during Single-Phase DC Excitation >
The relations between the voltages and currents occurring when single-phase DC
excitation is done under the condition where the plural values of the measuring voltage of Vdl,
Vd2, and Vd3 are applied to the d-axis command voltage Vdref in turn are next described.
W6882
- 13-
FIGS. 3 A and 3B are diagrams illustrating the relation between the u-phase
detection current lu and the w-phase detection current Iw when the d-axis and u-phase are made
coincident in phase and the measuring voltages of Vdl, Vd2, and Vd3 are applied to the d-axis
command voltage Vdref FIG. 3 A shows a vector relation obtained when the measuring
5 voltages of Vdl, Vd2, and Vd3 are applied to the d-axis command voltage Vd (Vdref) on the daxis.
FIG. 3B shows the vector relation between u-phase, v-phase, and w-phase and the vector
relation between the u-phase detection current lu and the w-phase detection current Iw. FIG. 3C
shows the association between the d-axis command voltage Vd, the u-phase detection current lu,
and the w-phase detection current Iw. FIG. 3D shows an expression interrelating the u-phase
10 detection current lu and the w-phase detection current Iw under the condition where the current
detection unit is in a normal state.
FIG. 3 A shows a case in which the measuring voltages of Vdl, Vd2, and Vd3 are
applied in the direction of the d-axis. Note that Vdl < Vd2 < Vd3 and that the u-phase and the
d-axis are shown to be in the same direction.
15 As shown in FIG 3B, application of the measuring voltages of Vdl, Vd2, and
Vd3 in the direction of the d-axis results in the u-phase detection currents lul, Iu2, and Iu3.
Also, the w-phase detection currents Iwl, Iw2, and Iw3 are produced. The u-phase, v-phase,
and w-phase are vectorially spaced from each other in phase (phase angle) by 120 degrees
(27C/3).
20 The w-phase detection currents Iwl, Iw2, and Iw3 are produced as negative
components on the opposite side of the original w-phase (i.e., spaced by 180 degrees (TT)). That
is, the negative axis of the w-phase and the u-phase are vectorially spaced from each other by 60
degrees (%/3). In the following description, an angle (phase angle) corresponding to a phase
angle is indicated in radians rather than in degrees. For instance, a phase difference of 120
25 degrees is indicated by 27t/3.
For example, as shown in FIG. 3B, there is a phase difference of 7t/3 between the
u-phase detection current Iu3 and the negative (-) w-phase detection current Iw3 located on the
opposite side of the w-phase. Because of the relation of a projection of the u-phase detection
current Iu3 onto the axis of the w-phase, if expressed including both positive and negative
30 directions, there is a relation given by - Iw3 = Iu3 x cos (K/3) = Iu3 x (1/2). Accordingly, we
have
Iu3 = - 2 X Iw3 (3)
W6882
14-
Similarly,
Iu2 - - 2 X Iw2 (4)
lul - - 2 X Iwl (5)
5 FIG. 3C shows the above-described relations among the u-phase detection
currents lul, Iu2, and Iu3 and the w-phase detection currents Iwl, Iw2, and Iw3. The u-phase
detection currents lul, Iu2, and Iu3 rise in steps together with the d-axis command voltage Vd
(Vdl, Vd2, and Vd3). The w-phase detection currents Iwl, Iw2, and Iw3 increase in absolute
value incrementally in the negative direction in step with the d-axis command voltage Vd (Vdl,
10 Vd2, and Vd3).
The d-axis command vohage Vd (Vdl, Vd2, and Vd3) is a direct current voltage.
The u-phase detection currents lul, Iu2, Iu3 and the w-phase detection currents Iwl, Iw2, and
Iw3 are DC currents. Therefore, the various values are denoted linearly.
FIG. 3D shows a formula interrelating the u-phase detection currents lul, Iu2, Iu3
15 and the w-phase detection currents Iwl, Iw2, and Iw3 in a case where the current detection unit
is in a normal state. These expressions correspond to Eqs. (3), (4), and (5). A decision is
made as to whether the current detection unit 50 (51, 52) is normal or abnormal, including its
connective state, depending on whether Eqs. (3), (4), and (5) hold at the same time.
< Summary of Configuration and Method of the First Embodiment >
20 In the first embodiment of the present invention described so far, the following
configuration and method are adopted.
(1) The AC motor Control unit 24 of the present invention has: the power
converter 20 for converting a supplied electric power into an electric power of variable voltage
and variable fi^equency and driving the AC motor 30 at a variable speed; the PWM (pulse width
25 modulation) control unit 45 for controlling the power converting function of the power converter
20; and the current detection unit abnormality decision device 48 having the command voltage
calculating means 47 used for decision on abnormality and outputting the command voltage
signal for making a decision as to whether there is any abnormality in the current detection unit
50 operating to detect electrical currents flowing through the AC motor 30 and the abnormality
30 decision means 46 for making a decision as to whether there is any abnormality in the current
detection unit 50, depending on a pattern of electrical currents obtained fi-om the current
detection unit 50 by applying the command voltage signal to the power converter 20 for driving
the motor The PWM control unit 45 supplies the control signal 43 S to the power converter 20
for driving the motor, based on the external command signal 45 S and on the detection signals
W6882
- 15-
from the current detection unit 50. When the current detection unit abnormality decision device
48 determines that there is abnormality in the current detection unit 50 prior to operation of the
AC motor 30, the AC motor Control unit provides an output for displaying abnormality.
(2) Alternatively, the AC motor Control unit 24 is so configured that the
5 abnormality decision command voltage calculating means 47 supplies a given command signal
for abnormality decision on the current detection unit 50 to the power converter 20. This
calculating means 47 furnishes a command signal to apply plural voltages (FIG. 3 A) to phases of
the AC motor 30 before the AC motor Control unit 24 is operated.
(3) Alternatively, the AC motor Control unit 24 is so configured that the
10 abnormality decision command voltage calculating means 47 for supplying the command voltage
signal to the power converter modifies the magnitude of the DC voltage applied to the AC motor
30 to plural levels (FIG. 3 A).
(4) Alternatively, the AC motor Control unit 24 is so configured that the
abnormality decision means 46 determines that the current detection unit 50 is damaged or
15 abnormally connected (not connected or wiring breakage) if the output level from the current
detection unit 50 is equal to or less than a given level and detected as the same value within a
given range of levels when the DC vohage is applied by the abnormality decision command
vohage calculating means 47 while incrementally varying its magnitude. The AC motor
Control unit 24 outputs a warning of abnormality in the current detection unit (S24 of FIG 2).
20 (5) Alternatively, the AC motor Control unit 24 is so configured that the
abnormality decision device 46 determines that there is a damage error or wire breakage error
(including non-connection) in the current detection unit 50 (S27 of FIG. 2).
(6) Alternatively, the AC motor Control unit 24 is so configured that when
vohages are applied, if the output signals from the plural current detection units are found to vary
25 beyond a given level compared with when an incrementally varied voltage is applied and if the
ratio of the output signals from the two current detection units does not agree with any one of
patterns < 1 > ± 2 times, < 2 > ± 1 times, and < 3 > ± 1/2 times as shown in FIG. 3D within a
given range of levels, the abnormality decision means 46 determines that there is damage to the
current detection unit 50. A warning of abnormality in the current detection unit is outputted
30 from the AC motor Control unit 24 (S28 of FIG. 2).
(7) Alternatively, the AC motor Control unit 24 is so configured that the
abnormality decision means 46 determines that the current detection unit 50 suffers from a
damage error (S28 of FIG. 2).
< Advantageous Effects of the First Embodiment >
W6882
-16-
Because of the configuration and method of the first embodiment described so far,
it is possible to previously detect whether the current detection unit 50 is normally connected
with the output terminals of the power converter 20 by applying plural voltages for detection of
abnormality in the current detection unit 50. Accordingly, damage to the AC motor Control
5 unit 24 is prevented; otherwise, increased losses would occur.
Where the AC motor Control unit 24 has an automatic tuning function, the
soundness of the current detection unit can be checked by utilizing the operation of the automatic
tuning. Furthermore, prior to operation, the soundness of the current detection unit can be selfchecked.
Checking the current detection unit contributes to improvement of the accuracy of the
10 automatic tuning. The checking operation can be performed without removing the current
detection unit. Additionally, the checking operation can be carried out only in software without
adding any hardware for checking the current detection unit. This method can shorten the
makeover time with less cost increase. It is possible to offer the AC motor Control unit 24
having the fiinctions and advantageous effects described so far.
15 (Second Embodiment)
An example in which the AC motor Control unit 24 shown in FIG. 1 is operated
by a second control method is described as a second embodiment of the present invention. The
second embodiment has the functions and advantageous effects achieved by the first
embodiment, i.e., it is possible to previously check whether the current detection unit is normally
20 connected. Furthermore, the AC motor Control unit 24 adds such function and advantageous
effects that a misconnected location can be identified and a normal connection destination can be
displayed. The configuration of, and method implemented by, the AC motor Control unit 24
are described below.
In order to run the AC motor 30 normally using the AC motor Control unit 24, it
25 is necessary to check that the current detection unit 50 including detecting units 51, 52 is
normally connected. For example, during manufacture of the AC motor Control unit, a work
for connecting the current detection unit 50 (51, 52) with cable that connects together the output
terminals of the power converter 20 and the AC motor 30 takes place.
Furthermore, in the first embodiment, if the current detection unit is judged to
30 have a damage error and the current detection unit 50 needs to be replaced, then it is necessary
that the cable connecting together the output terminals of the power converter 20 and the AC
motor 30 and the current detection unit 50 connected to the cable be removed and that a new
current detection unit 50 be connected.
However, similar types are normally used as the cable and current detection unit
W6882
- 17-
50 for every phase and so when the current detection unit 50 is connected, there is the possibility
that the output terminals of the power converter 20 and the current detection unit 50 will be
connected to different phases (misconnections). In addition, it is difficult to visually check the
connection after the connection has been completed because similar types are used as the cable
5 and current detection unit 50 for every phase.
Accordingly, in the second embodiment, single-phase DC excitation is done in the
same way as in the first embodiment. The resuhs of detection of the currents are analyzed to
make a decision as to whether the current detection unit 50 (51, 52) is normally connected with
corresponding phases of the terminals u, v, and w of the power converter 20. If the result of
10 decision is that there is abnormality, a normal connection destination is shown.
< Second Control Method (first aspect) for Current detection unit Abnormality Decision Mode >
Details of a measuring method according to a second control method of the
second embodiment are described below. In the same way as in the first embodiment, it is
assumed in the second embodiment that the current detection unit 50 is connected with two
15 output terminals of u-phase and w-phase out of the output terminals of u-, v-, and w-phases of
the power converter 20.
< Method of Applying d-axis Command Voltage Vd >
FIGS. 4A-4C are diagrams illustrating the manner in which the AC motor Control
unit 24 of the present invention applies the d-axis command voltage Vd (Vdl, Vd2, and Vd3) by
20 the second control method. FIG 4A shows a case in which 9d = 0. FIG. 4B shows a case in
which 0d = 27C/3. FIG. 4C shows a case in which 9d = 47r/3. As mentioned previously, 9d is
the phase difference between the u-phase and the d-axis, i.e., a phase angle.
In FIG. 4A, the d-axis lies in the same direction as the u-phase. The d-axis
command voltage Vd (Vdl, Vd2, Vd3) is applied in the same direction (0d = 0) as the u-phase.
25 The d-axis command voltage Vd is used to apply three voltages Vdl, Vd2, and Vd3, and
measurements are performed.
In FIG. 4B, the phase difference 9d between the u-phase and the d-axis is
modified to 27i/3. Consequently, the d-axis is in the same direction as the v-phase. Under this
condition, the d-axis command voltage Vd is used to apply the three voltages Vdl, Vd2, and Vd3
30 and to perform measurements.
In FIG. 4C, the phase difference 9d between the u-phase and the d-axis is
modified to 47t/3. The d-axis is in the same direction as the w-phase. Under this condition,
the d-axis command vohage Vd is used to apply the three vohages Vdl, Vd2, and Vd3, and
W6882
-18-
measurements are performed.
< Misconnection of Current detection unit >
A case in which the current detection units 51 and 52 are misconnected with the
power converter 20 is next described. FIGS. 5 A and 5B show the connective relation between
5 the power converter 20 and the current detection units. FIG. 5 A shows a normal connection.
FIG. 5B shows a misconnected connection.
In FIG. 5A, the current detection unit 51 is used to detect the u-phase current.
The current detection unit 52 is used to detect the w-phase current. These detection units are
connected normally.
10 In FIG. 5B, the current detection unit 51 for detection of the u-phase current is
connected with the w-phase of the power converter 20, while the current detection unit 52 for
detection of the w-phase current is connected with the u-phase of the power converter 20. Such
a misconnection might occur in a case where current detection units are mounted newly or in a
case where the detection units become defective and are replaced.
15 < Relation between lu and Iw at 9d == 0, 27t/3, and 47i/3 >
The relation between lu and Iw when the phase difference Gd between the u-phase
and the d-axis is varied to 0,1%I2, and 47c/3 is next described.
FIGS. 6A-6C are diagrams illustrating the relation between lu and Iw when the
phase difference 0d between the u-axis and the d-axis is varied under a second set of measuring
20 conditions (condition 2) while the terminals of the power converter 20 of the AC motor Control
unit 24 associated with the second embodiment of the present invention and the current detection
units 51 and 52 are normally connected. FIG. 6A shows a case in which 9d = 0. FIG. 6B
shows a case in which 0d = 27t/3. FIG. 6C shows a case in which 0d = 47i/3.
The second set of measuring conditions involves: first-order angular frequency
25 command ©Iref = 0 and q-axis command voltage Vqref = 0. Furthermore, the measuring
voltage Vd that is varied from Vdl to Vd2 and then to Vd3 is applied to the d-axis command
vohage Vdref The phase difference 9d between the u-phase and the d-axis is varied to 0, 2TC/3,
and 47t/3, and single-phase DC excitation is done.
In FIGS. 6A-6C, current lu (lul, Iu2, Iu3) detected at the u-phase and current Iw
30 (Iwl, Iw2, Iw3) detected at w-phase under the second set of measuring conditions are shown.
« In the case of 0d = 0 »
In the case of FIG. 6A, the same relation as in FIGS. 3A-3C holds. Therefore,
Eqs. (3)-(5) calculated based on the FIG. 3B hold. As a consequence, expressions given by
W6882
-19-
equation set (1) are obtained. That is,
I u l - - 2 x l w l , Iu2 = - 2 x l w 2 , Iu3 = - 2 x l w 3 (1)
5 « In the case of 9d = 27t/3 »
In the case of FIG. 6B, the direction of the d-axis is coincident with the v-phase.
Therefore, the w-phase detection currents Iwl, Iw2, and Iw3 are produced as negative
components on the opposite side of the original w-phase (spaced by 180 degrees (%)). That is,
the negative axis of the w-phase and the v-phase are vectorially spaced from each other by 7t/3.
10 For example, when expressed including the positive and negative directions, the
relation between the v-phase detection current Iv3 and the w-phase detection current is that Iv3
of the v-phase is projected in the negative direction of the w-phase at an angle of 7i/3.
Therefore, the following equation holds:
15 - Iw3 = Iv3 X cos (7C/3) = Iv3 x (1/2)
Thus, we have
Iv3 = - 2 X Iw3 (6)
The u-phase detection currents lul, Iu2, and Iu3 are produced as negative
20 components on the opposite side (spaced apart by 7C (180 degrees)) of the original u-phase.
That is, the negative axis of the u-phase and the v-phase are vectorially spaced from each other
by 7t/3.
When expressed including the positive and negative directions, the relation
between the v-phase detection current Iv3 and the u-phase detection current is that Iv3 of the v-
25 phase is projected in the negative direction of the u-phase at an angle of 7i/3. Therefore, the
following equation holds:
- Iu3 = Iv3 X cos (7i/3) = Iv3 x (1/2)
Thus, we have
30 Iv3 = - 2 X Iu3 (7)
Eqs. (6) and (7) lead to
Iu3 = Iw3 (8)
Similarly, there exist relations given by
W6882
-20-
Iul=Iwl, Iu2 = Iw2, Iu3 = Iw3 (9)
« In the case of 0d = 47u/3 »
In the case of FIG 6C, the direction of the d-axis is coincident with the w-phase
5 and so the w-phase detection currents Iwl, Iw2, and Iw3 are outputted intact. The u-phase
detection currents lul, Iu2, and Iu3 are produced as negative components on the opposite side of
the original u-phase. That is, the negative axis of the u-phase and the w-phase are vectorially
spaced from each other by 7t/3. When expressed including the positive and negative directions,
the relation between the u-phase detection current Iu3 and the w-phase detection current Iw3 is
10 given by
- Iu3 = Iw3 X cos (7t/3) = Iw3 x (1/2)
Thus, we have
Iu3 = - ( l / 2 ) x l w 3 (10)
15 Similarly, we can have the relations:
lul =-(1/2) X Iwl, Iu2--(l/2)xlw2, Iu3--(1/2) xlw3 (11)
Therefore, when equation sets (1), (9), and (11) hold, it is possible to determine that the current
detection units 51 and 52 are normally connected. When the equations do not hold, it is
20 possible to determine that the current detection units 51 and 52 are misconnected.
< Relation between lu and Iv at 9d = 0, 27c/3, 47t/3 >
The relation between lu and Iv occurring when the phase difference 9d between
the u-phase and the d-axis is varied from 0 to 27i/3 and then to 47i/3 is next described. FIGS.
7A-7C are diagrams illustrating the relation between lu and Iv in a case where the phase
25 difference 9d between the u-phase and the d-axis is varied under the above-described second set
of measuring conditions while the terminals of the power converter 20 of the AC motor Control
unit 24 associated with the second embodiment of the present invention and the current detection
units 51, 52 are normally connected. FIG. 6A shows a case in which 0d = 0. FIG. 6B shows a
case in which 0d = 27t/3. FIG. 6C shows a case in which 9d = 45T/3 .
30 « In the case of 9d = 0 »
In the case of FIG. 7A, the direction of the d-axis is coincident with the u-phase.
Therefore, the v-phase detection currents Ivl, Iv2, and Iv3 are produced as negative components
on the opposite side of the original v-phase. That is, the negative axis of the v-phase and the uW6882
- 2 1 -
phase are vectorially spaced from each other by 7i/3.
For example, when expressed including the positive and negative directions, the
relation between the u-phase detection current Iu3 and the v-phase detection current is that Iu3 of
the u-phase is projected in the negative direction of the v-phase at an angle of 7i/3. Therefore,
5 we have
- Iv3 = Iu3 X cos (7C/3) = Iu3 x (1/2)
This leads to
Iu3 = - 2 x l v 3 (12)
10 Similarly, there exist relations given by
I u l = - 2 x l v l , Iu2 = - 2 x l v 2 , Iu3=-2xlv3 (13)
« In the case of 6d = 27t/3 »
In the case of FIG. 7B, the direction of the d-axis is coincident with the v-phase
15 and so the u-phase detection currents lul, Iu2, and Iu3 are produced as negative components on
the opposite side of the original u-phase. That is, the negative axis of the u-phase and the vphase
are vectorially spaced from each other by 7c/3.
For example, when expressed including the positive and negative directions, the
relation between the v-phase detection current Iv3 and the u-phase detection current is such that
20 Iv3 of the v-phase is projected in the negative direction of the u-phase at an angle of 7t/3. Thus,
we have
- Iu3 = Iv3 X cos (7C/3) = Iv3 x (1/2)
Accordingly, we can have
25 Iu3 = - (1/2) X Iv3 (14)
Similarly, there exist relations given by
I u l - - ( l / 2 ) x l v l , Iu2 = - ( l / 2 ) x l v 2 , Iu3 =-(1/2) xlv3 (15)
« In the case of 0d - 4K/3 »
30 In the case of FIG. 7C, the direction of the d-axis is coincident with the w-phase
and, therefore, the u-phase detection currents lul, Iu2, and Iu3 are produced as negative
components on the opposite side of the original u-phase That is, the negative axis of the uphase
and the w-phase are vectorially spaced from each other by K/3.
W6882
- 2 2 -
For example, when expressed including the positive and negative directions, the
relation between the w-phase detection current Iw3 and the u-phase detection current Iu3 is such
that Iw3 of the w-phase is projected in the negative direction of the u-phase at an angle of 7t/3.
Thus, we have
5
- Iu3 = Iw3 X cos (7i/3) = Iw3 x (1/2)
This results in
Iu3 = - (1/2) X Iw3 (16)
10 Furthermore, the v-phase detection currents Ivl, Iv2, and Iv3 are produced as
negative components on the opposite side of the original v-phase. That is, the negative axis of
the v-phase and the w-phase are vectorially spaced from each other by 7r/3.
For example, when expressed including the positive and negative directions, the
relation between the w-phase detection current Iw3 and the v-phase detection current Iv3 is such
15 that Iw3 of the w-phase is projected in the negative direction of the v-phase at an angle of 7t/3.
Therefore, the following relations hold:
- Iv3 = Iw3 X cos (7t/3) = Iw3 x (1/2)
This results in
20 Iv3 = - (1/2) X Iw3 (17)
Eqs. (16) and (17) lead to
Iu3 = Iv3
Similarly, there exist relations given by
l u l ^ I v l , Iu2 = Iv2, Iu3=Iv3 (18)
25
< Relation among lu, Iv, and Iw at 0d = 0, 27c/3, 47i/3 >
The relation among lu, Iv, and Iw occurring at various values of 0d is next
described. First, the relation among lul, Ivl, and Iwl is explained.
«In the case of 0d = 0 »
30 From equation sets (1) and (13), the following equations can be obtained:
lul = - 2 X Ivl, lul = - 2 X Iwl, Ivl = Iwl (19)
W6882 [
i
- 2 3 -
The relation between (Iu2, Iv2, Iw2) and (Iu3, Iv3, Iw3) can be expressed by similar equations.
«In the case of 8d = 27t/3 »
From Eqs. (9) and (15), we can have
5 Iul=-(l/2)xlvl, Iul=Iwl, Ivl - - (1/2) X Iwl (20)
The relation between (Iu2, Iv2, Iw2) and (Iu3, Iv3, Iw3) can be expressed by similar formulas.
« In the case of 0d = 4K/3 »
From equation sets (11) and (18), we can have
10
Iul=Ivl, I u l = - ( l / 2 ) x l w l , Ivl = - (1/2) Iwl (21)
The relations between (Iu2, Iv2, Iw2) and (Iu3, Iv3, Iw3) can be expressed by similar formulas.
< Relations between Connection Positions of Current detection units and Detection Currents >
15 The relations between positions at which the u-phase current detection unit 51 and
w-phase current detection unit 52 are connected in the current detection unit 50 and detection
currents occurring at 9d = 0, 27t/3, and 47t/3 are described. These are exploited when an
inspection is performed to see if the current detection units are placed at correct positions and
connected in a work for replacing at least one of the detection units because of failure as
20 described later
FIG 8 is a table showing the relations among the detection currents lu, Iv, and Iw
from the current detection unit 50 occurring when single-phase DC excitation is done after the
position at which the current detection unit 50 is connected and 0d are varied for the u-, v-, and
w-phases of the output terminals of the power converter 20.
25 In FIG. 8, various combinations (Case) of positions at which the current detection
units are connected are represented as C1-C6 in the first column as viewed from the left side.
Positions at which the current detection units are connected are shown in the second column as
viewed from the left side. The u-phase current detection unit 51 and the w-phase current
detection unit 52 are connected between the power converter 20 and the AC motor 30 in six
30 patterns of connection positions.
Theoretical formulas interrelating the detection currents Iul-Iu3 and Iwl-Iw3 are
shown in the third to fifth columns as viewed from the left side at 0d = 0, 27r/3, and 4K/3,
respectively.
W6882
-24-
In the case of the combination CI, the u-phase current detection unit 51 and the
w-phase current detection unit 52 are correctly positioned and connected.
In the case of the combination C2, the u-phase current detection unit 51 and the
w-phase current detection unit 52 have been interchanged and connected.
5 In the case of the combination C3, the w-phase current detection unit 52 which
should be connected with the w-phase has been connected with the v-phase.
In the case of the combination C4, the u-phase current detection unit 51 and the
w-phase current detection unit 52 have been interchanged wrongly and connected under the
combination C3.
10 In the case of the combination C5, the u-phase current detection unit 51 that
should be connected with the u-phase has been connected with the v-phase.
In the case of the combination C6, the u-phase current detection unit 51 and the
w-phase current detection unit 52 have been interchanged wrongly and connected under the
combination C5.
15 Theoretical formulas interrelating the detection currents Iul-Iu3 and Iwl-Iw3 at
0d = 0, 27i/3, and 47i/3 at the combinations C1-C6 are based on above equation sets (19)-(21).
< Second Control Method (second aspect) in Current detection unit Abnormality Decision Mode
>
A decision made as to whether the current detection unit 50 is normally connected
20 is described by referring to the flowchart of FIG. 9. Also, a current detection unit abnormality
decision mode (second control method) in which misconnection of the current detection unit 50
and phases with which the current detection unit 50 is connected during measurement are judged
is described by referring to the flowchart of FIG. 9.
< Flowchart illustrating Current detection unit Abnormality Decision Mode (second control
25 method) >
FIG 9 is a flowchart illustrating a decision made as to whether the AC motor
Control unit 24 associated with the second embodiment of the present invention is connected
normally with the current detection unit 50, as well as a decision made as to whether the current
detection unit is misconnected. The flowchart also sets forth a method of judging the phases
30 with which the current detection unit is connected during measurement, as well as a method of
displaying a normal connection destination. Processing steps of the method of judging
abnormality are described in turn with reference to FIG. 9.
« Step S51 »
Step S51 is performed to enter rated voltage VI and rated current II that
W6882
- 2 5 -
constitute nameplate information about the motor. This information is used to indicate a
reference for a set range of measured vokages in an abnormality detection mode (described later)
and a reference for current values of the current detection unit. In FIG. 9, this step S51 is stated
as "Input of nameplate information (rated voltage and rated current)".
5 « Step S52 »
Step S52 is performed to output and apply a command voltage to detect
abnormality in the current detection unit 50 (FIG. 1). That is, this step is used to place the mode
of operation in the current detection unit abnormality decision mode.
In particular, as described previously, the switching elements Sd, Sq2, and Sa)2 of
10 the switch 49 (FIG. 1) are brought to the terminals Sd2, Sq2, and Sa)2, respectively, to disconnect
the vector control unit 41. The three-phase AC voltage coordinate converter 42 is informed of
measuring conditions under which the command voltage calculator 47 for abnormality decision
detects abnormality in the current detection unit.
The second set of measuring conditions (condition 2) is that: first-order angular
15 frequency command ©Iref = 0, phase difference 0d between u-phase and d-axis is 0 at first, qaxis
command voltage Vqref = 0, plural measuring voltages of Vdl, Vd2, Vd3 are applied to the
d-axis command voltage Vdref, and single-phase DC excitation is done when the phase
difference 0d between the u-phase and the d-axis is varied to 27i/3 and then to 47i/3. In FIG. 9,
this step S52 is stated as "Abnormality detection mode 1: single-phase DC excitation, condition
20 2".
« Step S53 »
Step S53 is performed to detect the u-phase current and w-phase current or vphase
current delivered from the power converter 20 by the u-phase current detection unit 51 and
w-phase current detection unit 52 of the current detection unit 50 under the measuring conditions
25 of step S52. In FIG. 9, this step S53 is stated as "Deteaion of u-phase current and w-phase
current".
« Step S54 »
Step S54 is performed to analyze the u-phase current and the w-phase current (or
the v-phase current) obtained at step S53. lu and Iw are obtained from the u-phase current
30 detection unit 51 and the w-phase current detection unit 52, respectively, when single-phase DC
excitation is done while varying 0d and currents are detected. The relation between the lu and
Iw can be represented by the following three patterns:
< 1 >: lu = - 2 X Iw
W6882
-26-
< 2 >: lu = Iw
< 3 >: lu = - 1/2 X Iw (22)
That is, an analysis is performed to know to what of the formulas < 1 >, < 2>, and < 3 > of
5 equation set (22) does the relation between the u-phase current lu and the w-phase current Iw
correspond. In FIG. 9, this step S54 is stated as "Analysis of relation between lu and Iw at 0d =
0, 271/3, 471/3".
« Step S55 »
Step S55 is performed to detect what combination does the relation between lu
10 and Iw obtained at step S54 match. FIG. 10 is a table showing combinations of formulas
interrelating the detection currents lu and Iw from the current detection units, as well as the
corresponding relationship (pattern matching) to the connective state of the current detection unit
50.
The table of FIG. 10 contains a horizontal row having items of the combinations
15 (Case) C1-C6. The table also contains a vertical row having items of 9d (= 0, 27c/3, 47c/3). In
this step S55, it is possible to know to what of the combinations C1-C6 does the relation between
lu and Iw at each value of 9d correspond by comparing the results (one equation of equation set
(22)) with the table of FIG. 10.
For example, where both current detection units 51 and 52 are connected
20 normally, the equation < 1 > lu = - 2 x Iw holds at 9d = 0. The equation < 2 > lu = Iw holds at
9d = 27c/3. The equation < 3 > lu = - 1/2 x Iw holds at 9d = 47c/3. Therefore, it is determined
that case CI of FIG. 10 is pertinent.
Where the current detection unit 51 for detection of u-phase current is connected
with the w-phase of the output terminals of the power converter 20 and the current detection unit
25 52 for detection of w-phase current is connected with the u-phase of the output terminals of the
power converter 20, the equation < 3 > lu = - 1/2 x Iw holds at 9d = 0. The equation < 2 > lu =
Iw holds at 9d = 27c/3. The equation < 1 > lu = - 2 x Iw holds at 0d = 47r/3. Therefore, it is
determined that case C2 of FIG. 10 is pertinent.
Similarly, from the formulas interrelating 9d, lu, and Iw, the states of connection
30 of the current detection unit 50 are classified as CI to C6. In FIG. 9, this step S55 is stated as
"Pattern Matching".
« Step S56 »
Step S56 is performed to make a decision as to whether the current detection unit
W6882
-27-
50 is connected normally. If the connection is normal (Case), only CI of FIG. 10 is pertinent.
Therefore, if the connective state is CI (Yes at S56), control goes to step S57.
If the connective states are C2 to C6 (No at S56), control proceeds to step S58.
In FIG. 9, this step S56 is stated as "Case = CI?".
5 « Step 57»
Step S57 is performed to determine that the connective state is normal and to
provide a display of the result of this decision. In step S56, the decision is Yes, i.e., the
connective state is CI. Control goes to step S57, where the connection is judged to be normal.
A display of a normal state or a state corresponding to a normal state is provided.
10 At the stage where a "normal" state is displayed, control goes to "END", thus
terminating this subroutine for making a decision on the connection of the current detection unit.
In FIG. 9, this step S57 is stated as "Decision is normal connection. Display".
« Step S58 »
Step S58 is performed when the decision at step S56 is No, i.e., the connective
15 state is not CI. In the cases of C2-C6 other than C1, there is any abnormality. Therefore, in
step S58, it is determined that there is abnormality. A display of abnormality or a state
corresponding to abnormality is provided.
In step S60 described later, a normal connection destination is displayed and so if
this display provided at step S60 can also display abnormality, a display of abnormality at step
20 S58 may be omitted.
In step S58, a display indicating "abnormality" is provided as the need arises.
Then, control goes to step S59. In FIG. 9, this step S58 is stated as "Decision is abnormal
connection. Display".
« Step S59 »
25 Step S59 is performed to judge the misconnected current detection unit and the
phase with which this detection unit is connected.
FIG. 11 is a table showing states of connection (Case) judged by pattern matching
of the detection currents from the current detection units, as well as the corresponding
relationship between the misconnected current detection unit and the phase with which this
30 detection unit is connected.
The table of FIG. 11 contains a horizontal row of items of C2-C6 about two cases
(Case). The table also contains a vertical row of items of the u-phase current detection unit and
the w-phase current detection unit. In the case of CI, the connection is normal and so the table
of FIG 11 does not contain CI.
W6882
-28-
In step S59, a decision is made as to what of the combinations C2-C6 of FIG. 11
is pertinent. The misconnected current detection unit and the phase with which this current
detection unit is connected are judged depending on the pertinent combination (any one of C2-
C6).
5 For example if the decision is that the combination C2 is pertinent, it is meant that
the current detection unit for detection of the u-phase current is connected with the w-phase of
the output terminals of the power converter and that the current detection unit for detection of wphase
current is connected with the u-phase of the output terminals of the power converter.
Decisions are made on these combinations C2-C6. The phase of the wrong connection
10 destination is judged. Then, control goes to step S60. In FIG. 9, this step S59 is stated as
"Decision is Wrong Connection Destination".
« Step S60 »
Step S60 is performed to display a phase with which the current detection unit
should be correctly connected, based on the judged combination (Case) of states of connections
15 C2-C6.
FIG. 12 is a table showing states of connection (Case) judged by pattern matching
of the detection currents from the current detection units, as well as the corresponding
relationship between misconnected current detection unit and the normal connection destination
of this current detection unit.
20 The table of FIG. 12 contains a horizontal row of the items of C2-C6 for each
combination (Case). The table also contains a vertical row of the items of the u-phase current
detection unit and the w-phase current detection unit. It is possible to judge the misconnected
current detection unit and the normal connection destination of this detection unit by knowing to
what of C2-C6 of FIG. 12 does the connection correspond.
25 For example, if the decision is that the combination C2 is pertinent, the current
detection unit 51 (FIG. 8) for detection of the u-phase current is connected with the w-phase of
the output terminals of the power converter 20 (FIG. 8) and the current detection unit 52 (FIG. 8)
for detection of the w-phase current is connected with the u-phase of the output terminals of the
power converter 20. Therefore, a display is provided to prompt the user to vary the
30 connections. That is, the w-phase should be removed and reconnected with the u-phase. The
u-phase should be removed and reconnected with the w-phase.
In FIG. 12, if the connections of the current detection units 51 and 52 are correct,
an indication "HOLD" is displayed. At the stage when a "normal connection destination" is
displayed, control goes to "END", thus terminating this subroutine for making a decision on
W6882
-29-
connections of this current detection unit. In FIG. 9, this step S60 is denoted as "display of
normal connection destination".
Because of the method described so far, abnormality and misconnection of the
current detection units can be detected. A location at which a misconnection is made can be
5 identified. Also, a normal connection destination can be displayed.
< Summary of Configuration and Method of the Second Embodiment >
The second embodiment of the present invention adopts the following
configuration and method.
(8) The AC motor Control unit 24 of the present invention has: the power
10 converter 20 for converting a supplied electric power into an electric power of variable voltage
and variable frequency and driving the AC motor 30 at a variable speed; the PWM control unit
45 for controlling the power converting function of the power converter 20 for driving the motor;
and the current detection unit abnormality decision device 48 having the command vohage
calculating means 47 used for abnormality decision and outputting a command voltage signal to
15 make a decision as to whether there is any abnormality in the current detection unit operating to
detect electrical currents flowing through the AC motor 30 and the abnormality decision means
46 for making a decision as to whether there is any abnormality in the current detection unit 50
depending on a pattern of electrical currents obtained from the current detection unit 50 by
applying the command voltage signal to the power converter 20 for driving the motor. The
20 PWM control unit 45 supplies a control signal to the power converter 20 for driving the motor,
based on the external command signal 45S and on detection signals from the current detection
unit 50. The command voltage calculating means 47 used for abnormality decision supplies the
voltage command signal plural times to the power converter 20 for driving the motor while
varying the phase of the voltage command signal. The abnormality decision means 46
25 compares a detection current pattern assumed from a pattern of the voltage command signals
applied in turn with the detection signals from the current detection unit 50. If the detection
current pattern does not agree with the assumed detection current pattern, it is determined that
the current detection unit 50 is misconnected, and a warning is issued.
(9) Alternatively, in the AC motor Control unit 24, the abnormality decision
30 means 46 is so configured that the detection currents are classified (FIG. 10) depending on the
ratio between the output signals from two current detection units and on the phase set on
application of the command signal when the command voltage calculating means 47 used for
abnormality decision applies a DC voltage plural times while varying its magnitude and phase.
(10) Alternatively, in the AC motor Control unit 24, the abnormality decision
W6882
-30-
means 46 is so configured that it detects a misconnection of the current detection units according
to the results of the classification (FIG. 10).
(11) Alternatively, in the AC motor Control unit 24, the abnormality decision
means 46 is so configured that when a misconnection is detected, the decision means 46 judges
5 previously set patterns of misconnections (FIG. 11), according to the results of the classification
(FIG. 10) which has been performed according to the ratio of the output signals fi^om the two
current detection units and on the phase set during application of the command signal.
(12) Alternatively, in the AC motor Control unit 24, the abnormality decision
means 46 is so configured that it outputs a preset connection destination modification pattern
10 (FIG. 12) according to a pattern of misconnections (FIG. 11).
< Advantageous Effects of the Second Embodiment >
Because of the configuration and method of the second embodiment described so
far, an AC motor Control unit can be offered which can previously check whether the current
detection unit is normally connected with the output terminals of the power converter.
15 Furthermore, the Control unit can detect abnormality and misconnection in the current detection
unit. In addition, the Control unit can identify the location of the misconnection. Further, the
Control unit can display a normal connection destination.
(Other Embodiments)
Although some embodiments of the present invention have been so far described
20 in detail with reference to the drawings, the invention is not restricted to these embodiments and
their modifications. The design may be varied without departing fi-om the gist of the present
invention. Some examples thereof are given below.
« The number of variations in the applied vohage »
A case in which a measuring vohage assuming three levels of Vdl, Vd2, and Vd3
25 is applied to the d-axis command voltage Vdref is exemplified in the steps S22 and S23 of the
flowchart of FIG. 2 according to the first embodiment. The number of levels of the measuring
voltage is not restricted to three. In another method, the measuring vohage is varied between
two levels. In a further method, the measuring vohage is varied between four or more levels.
As a first stage, a measurement is performed with Vdl. If desired relations can
30 be grasped from the resuHs of the measurement, the process is terminated with this single
measurement. If uncertain resuhs have occurred by the use of only Vdl, the measuring voltage
may be varied according to the circumstances. For example, a second level of voltage, i.e., V2,
is used for measurements. A third level of voltage, i.e. Vd3, may also be used for
measurements.
W6882
-31-
In a fiirther method, the voltage Vdl is increased from a low level in steps or
continuously. When a reaction permitting execution of a desired measurement is observed, the
measurement is performed using the voltage occurring at the time of the observation. Only the
single measurement is carried out.
5 In these methods using three levels of voltage or less, the number of
measurements is reduced if the process progresses satisfactorily. This creates the possibility
that a normal state or an error can be displayed in a short time.
« Waveform of Applied Vohage »
A method of applying a measuring voltage of single-phase DC excitation to the d-
10 axis command voltage Vdref has been described in the steps S22 and S23 of the flowchart of
FIG. 2 according to the first embodiment. The voltage is not restricted to a direct current. In
another method, a single-phase alternating current (single-phase AC excitation) may be applied.
In this case, a sinusoidally expressed vohage is used as a measuring vohage instead of a constant
DC voltage at each level of Vdl, Vd2, and Vd3 on the d-axis command vohage.
15 Concomitantly, the measuring current assumes the form of a sinusoidal waveform. In addition,
plural measurements may contain measurements using DC vohages and measurements using an
AC vohage.
« Display »
The steps S26, S27, S28 of the flowchart of FIG. 2 and the steps S57, S58, S60 of
20 the flowchart of FIG 9 have steps for "displaying" obtained information. In this case, the
information may be displayed in various formats. The information may be represented by still
images. Alternatively, the information may be represented by motion pictures. Additionally,
warning sound or voice guidance may also be used. Further, these signals or information may
be transmitted to other devices with cable or wirelessly.
25 « Phases and Number of Current detection units »
In the description of the first embodiment (FIG. 1) and the second embodiment
(FIGS. 5-8), the current detection units pertain to u-phase and w-phase. Alternatively, v-phase
may also be used. Where there are three current detection units connected with all of the three
output terminals (u, v, w) of the power converter, decisions can be made similarly.
30 « Circuit Configuration of Power converter unit Control apparatus »
In FIG. 1, examples of circuit configurations of the PWM control unit 45, current
detection unit abnormalhy decision device 48, and switch 49 are shown. A command signal
delivered fi-om the abnormalhy decision command vohage calculator 47 of the current detection
unit abnormality decision device 48 is sent through the switch 49 located between the vector
W6882
- 3 2 -
control unit 41 of the PWM control unit 45 and the three-phase AC voltage coordinate converter
42. The circuit configuration is not restricted to this example. For instance, the command
signal delivered from the abnormality decision command voltage calculator 47 may be applied to
the pulse generation unit 43. In this way, the circuit configuration can assume various forms.
5 « Implementation of Power converter unit Control apparatus in hardware or software »
The power converter unit control apparatus 40 of FIG. 1 is shown to have the
vector control unit 41, three-phase AC voltage coordinate converter 42, pulse generation unit 43,
three-phase AC current coordinate converter 44, abnormality decision device 46, voltage
command calculator 47 for decision on abnormality, and switch 49. These circuits and devices
10 may be implemented in hardware or in software or in both.
Furthermore, the power converter unit control apparatus 40 may be made of a
CPU (central processing unit) or an MPU (microprocessing unit). The fiinctions of some or all
of the devices 41-44, 46, 47, and 49 may be implemented by computer programs. In addition, a
part or all of the power converter 20 and the power converter unit control apparatus 40 may be
15 made of a CPU or an MPU.
« Power Source »
In the example of FIG. 1, the power converter 20 equipped in the AC motor
Control unit 24 once converts the AC power from the AC source 10 into a DC power and
converts the DC power into an AC power of variable voltage and variable frequency to drive the
20 AC motor 30. The supplied power is not restricted to AC power supply. The power converter
20 may receive supply of DC power from a DC power source (not shown) and convert the DC
power into an AC power of variable voltage and variable frequency to drive the AC motor 30.
« Load »
In the example of FIG. 1, an AC motor is driven by the AC motor Control unit 24.
25 The load is not restricted to an AC motor If a load is powered with three-phase AC power, use
of the inventive AC power controller 24 is effective in making a decision as to whether the
current detection unit is normal or abnormal, and is advantageous where equipment is newly
installed or maintenance is carried out.

W6882
-33-
CLAIMS:
1. An AC motor Control unit (24) comprising:
a power converter (20) for converting a supplied electric power into an electric
power of variable voltage and variable frequency and driving an AC motor (30) at a variable
speed;
a PWM (pulse width modulation) control unit (45) for controlling the power
converting function of the power converter (20); and
a current detection unit abnormality decision device (48) having command
voltage calculating means (47) used for decision on abnormality and outputting a command
voltage signal for making a decision as to whether there is any abnormality in a current detection
unit (50) operating to detect electrical currents flowing through the AC motor (30) and
abnormality decision means (46) for making a decision as to whether there is abnormality in the
current detection unit (50), depending on a pattern of electrical currents obtained from the
current detection unit (50) by applying the command voltage signal to the power converter (20)
for driving the motor;
wherein the PWM control unit (45) supplies a control signal (43S) to the power
converter (20) for driving the motor (30), based on an external command signal (45S) and on
detection signals (5IS, 52S) from the current detection unit (50); and
wherein, when the current detection unit abnormality decision device (48)
determines that there is abnormality in the current detection unit (50) prior to operation of the
AC motor (30), the AC motor Control unit provides an output for displaying abnormality.
2. An AC motor Control unit (24) comprising:
a power converter (20) for converting a supplied electric power into an electric
power of variable voltage and variable frequency and driving an AC motor (30) at a variable
speed;
a PWM control unit (45) for controlling the power converting fiinction of the
power converter (20) for driving the motor (30); and
a current detection unit abnormality decision device (48) having command
voltage calculating means (47) used for decision on abnormality and outputting a command
voltage signal to make a decision as to whether there is any abnormality in a current detection
unit (50) operating to detect electrical currents flowing through the AC motor (30) and
abnormality decision means (46) for making a decision as to whether there is any abnormality in
the current detection unit (50) depending on a pattern of electrical currents obtained from the
current detection unit (50) by applying the command vohage signal to the power converter (20)
W6882
-34-
for driving the motor;
wherein said PWM control unit (45) supplies a control signal (43 S) to the power
converter (20) for driving the motor, based on the external command signal (45S) and on
detection signals (5IS, 52S) from the current detection unit (50);
wherein said command voltage calculating means (47) used for abnormality
decision supplies the voltage command signal plural times to the power converter (20) for
driving the motor while varying the phase of the voltage command signal; and
wherein said abnormality decision means (46) compares a detection current
pattern assumed from a pattern of the voltage command signals applied in turn with the detection
signals (5 IS, 52S) from the current detection unit (50) and, if the detection current pattern does
not agree with the assumed detection current pattern, determines that the current detection unit
(50) is misconnected and issues a warning.
3. The AC motor Control unit (24) according to claim 1 or 2,
wherein said current detection unit abnormality decision device (48) is configured
including a command voltage calculator (47) used for decision on abnormality and operating to
calculate a first-order angular frequency command, a d-axis command voltage, and a q-axis
command vohage and an abnormality decision device (46) for comparing detection currents of
various phases from the current detection unit (50), performing calculations, and making a
decision as to whether there is any abnormality.
4. The AC motor Control unit (24) according to claim 1 or 2,
wherein said PWM control unit (45) is configured including:
a three-phase AC current coordinate converter (44) for converting detection
currents of various phases entered from the current detection unit (50) into a d-axis current and a
q-axis current;
a vector control unit (41) for calculating a d-axis command voltage and a q-axis
command voltage for the AC motor (30) based on information about the d-axis current and the qaxis
current delivered from the three-phase AC current coordinate converter (44);
a three-phase AC voltage coordinate converter (42) for converting the d-axis
command voltage and the q-axis command voltage delivered from the vector control unit (41)
into a three-phase AC command voltage; and
a pulse generation unit (43) for converting the three-phase AC command voltage
into a PWM control signal.
5. The AC motor Control unit (24) according to claim 1 or 2, wherein some or all of
fiinctions of said AC motor Control unit (24) are implemented by computer programs.
W6882
-35-
6. A method of checking soundness of a current detection unit (50) for use in or with
an AC motor Control unit (24) which comprises:
power conversion means (20) for converting a supplied electric power into an
electric power of variable voltage and variable frequency and driving an AC motor (30) at a
variable speed;
PWM control means (45) for controlling the power converting ftmction of the
power conversion means (20) for driving the motor; and
current detection unit abnormality decision means (48) having a command
voltage calculating fiinction used for abnormality decision and for outputting a command voltage
signal to make a decision as to whether there is any abnormality in the current detection unit (50)
operating to detect currents flowing through the AC motor (30) and an abnormality deciding
fiinction of making a decision as to whether there is any abnormality in the current detection unit
(50) depending on a pattern of electrical currents obtained from the current detection unit (50) by
applying the command voltage signal to the power conversion means (20) for driving the motor;
said method comprising the steps of
supplying a control signal from the PWM control means (45) to the power
conversion means (20) for driving the motor, based on an external command signal (45 S) and on
detection signals (5IS, 52S) from the current detection unit (50); and
causing the current detection unit abnormality decision means (48) to provide an
output for displaying abnormality when the decision means (48) determines that there is
abnormality before the AC motor (30) is run.
7. A method of checking soundness of a current detection unit (50) for use in or with
an AC motor Control unit (24) according to claim 6, wherein said current detection unit
abnormality decision means (48) provides a command vohage signal to apply plural voltages to
various phases of the AC motor (30) before the AC motor (30) is run.
8. The method of checking soundness of a current detection unit (50) for use in or
with an AC motor Control unit (24) according to claim 7, wherein when said current detection
unit abnormality decision means (48) applies the command voltage signal of a DC vohage plural
times while varying its magnitude, if values that are substantially identical within a given range
of levels are detected, the current detection unit abnormality decision means (48) determines that
the current detection unit (50) is damaged or misconnected and causes the AC motor Control unit
(24) to output a warning of abnormality in the current detection unit (50).
9. The method of checking soundness of a current detection unit (50) for use in or
with an AC motor Control unit (24) according to claim 8, wherein when the warning of
W6882
-36-
abnormality in the current detection unit (50) is outputted, said current detection unit
abnormality decision means (48) determines that there is an error caused by non-connection of
the current detection unit (50), a damage to the current detection unit (50), or wire breakage.
10. The method of checking soundness of a current detection unit (50) for use in or
with an AC motor Control unit (24) according to claim 9, wherein when said current detection
unit abnormality decision means (48) applies the command voltage signal of a DC voltage plural
times while varying its magnitude, if a variation more than a given level is detected in response
to the applied vohage and if the ratio of output signals from two current detection units (51, 52)
of the current detection unit (50) agrees with none of three patterns which are respectively
delineated by < 1 > ± 2 times, < 2 > ± 1/2 times, and < 3 > + 1 times within a given range of
levels, the current detection unit abnormality decision means (48) determines that there is
damage to the current detection unit (50) and causes the AC motor Control unit (24) to output a
warning of abnormality in the current detection unit (50).
11. A method of checking soundness of a current detection unit (50) for use in or with
an AC motor Control unit (24) which comprises:
power conversion means (20) for converting a supplied electric power into an
electric power of variable voltage and variable frequency and driving an AC motor (30) at a
variable speed;
PWM control means (45) for controlling the power converting function of the
power conversion means (20) for driving the motor; and
current detection unit abnormality decision means (48) having command vohage
calculating means (47) used for decision on abnormality and for outputting a command voltage
signal to make a decision as to whether there is any abnormality in the current detection unit (50)
operating to detect currents flowing through the AC motor (30) and abnormality decision means
(46) for making a decision as to whether there is any abnormality in the current detection unit
(50) depending on a pattern of electrical currents obtained from the current detection unit (50) by
applying the command voltage signal to the power conversion means (20) for driving the motor;
said method comprising the steps of
supplying a control signal to said motor-driving power conversion means (20)
from said PWM control means (45) based on an external command signal (45 S) and on detection
signals (5IS, 52S) from said current detection unit (50);
supplying said command voltage signal plural times to said power conversion
means (20) for driving the motor while varying its phase from said command voltage calculating
means (47) for abnormality decision;
- 3 7 -
comparing a detection current pattern assumed from a pattern of the command
signal applied plural times with detection signals delivered from the current detection unit (50)
by said abnormality decision means (48); and
determining that said current detection unit (50) is misconnected and causing the
AC motor Control unit (24) to output a warning of abnormality in the current detection unit (50)
if no coincidence takes place with the assumed detection current pattern.
12. A method of checking soundness of a current detection unit (50) for use in or with
an AC motor Control unit (24) according to claim 11, wherein when said current detection unit
abnormality decision means (48) applies a DC voltage plural times to said power conversion
means (20) for driving the motor while varying the magnitude of the DC voltage, the current
detection unit abnormality decision means (48) classifies misconnections of the current detection
unit (50), depending on the ratio of output signals from two current detection units (51, 52) of the
current detection unit (50) and on phases set on application of the command signal.
13. The method of checking soundness of a current detection unit (50) for use in or
with an AC motor Control unit (24) according to claim 12, wherein said current detection unit
abnormality decision means (48) detects misconnections of the current detection unit (50)
according to results of the classification of misconnections of the current detection unit (50).
14. The method of checking soundness of a current detection unit (50) for use in or
with an AC motor Control unit (24) according to claim 12 or 13, wherein when a misconnection
is detected, said current detection unit abnormality decision means (48) judges a pattern of
detection currents created by the detected misconnection, based on results of the classification of
misconnections of the current detection unit (50) made depending on the ratio of output signals
from two detection units (51, 52) of the current detection unit (50) and on phases set on
application of the command signal.
15. A method of checking soundness of a current detection unit (50) for use in or with
an AC motor Control unit (24) according to claim 14, wherein said current detection unit
abnormality decision means (48) outputs a preset connection modifying pattern in response to a
pattern of detection currents created by the detected misconnection.
16. An AC motor Control unit, substantially as herein described with reference to
accompanying drawings and examples.
17. A method of checking soundness of a current detection unit, substantially as
herein described with reference to accompanying drawings and examples.