FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
INVERTER DEVICE AND INVERTER
DEVICE ANOMALY DETECTION METHOD;
MITSUBISHI ELECTRIC CORPORATION,
A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF
JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU,
TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH
IT IS TO BE PERFORMED.
2
DESCRIPTION
Field
5 [0001] The present invention relates to an inverter
device that includes a charging circuit that uses a
limiting resistor, and to an inverter device anomaly
detection method.
10 Background
[0002] A typical inverter device includes a smoothing
capacitor in an intermediate direct current (DC) unit.
Upon startup, such an inverter device rectifies an
alternating current (AC) voltage applied from an AC power
15 supply using a converter unit to charge the smoothing
capacitor. However, the smoothing capacitor is uncharged
in the initial charging process immediately after power-on,
and therefore, a high inrush current will flow. To reduce
or eliminate this inrush current in the initial charging
20 process, an inverter device includes a charging circuit
consisting of a resistor that serves as a limiting resistor,
and a contact element, such as a relay, for shortcircuiting across this resistor.
[0003] Patent Literature 1 listed below discloses a
25 technology to detect an anomaly of this charging circuit.
Patent Literature 1 describes detecting of the voltage
across a smoothing capacitor using an already-incorporated
voltage detector typically included for breakdown
protection of the smoothing capacitor and/or the like, thus
30 detecting a short-circuit fault or an open fault of the
contact element from the slope of the detected voltage
value based on a voltage detection signal detected, and
then displaying that a fault has occurred.
3
Citation List
Patent Literature
[0004] Patent Literature 1: Japanese Patent Application
5 Laid-open No. 2012-120376
Summary
Technical Problem
[0005] In Patent Literature 1, if the slope of voltage
10 rise of the voltage across the smoothing capacitor for a
predetermined time period after the contact signal has
reached a value representing an ON state is greater than or
equal to a reference value, it is determined that the
contact element does not have an open fault, i.e., the
15 contact element is in a normal condition. However, the
technology described in Patent Literature 1 suffers from a
problem that an anomaly of a charging circuit due to
deterioration of the limiting resistor and/or the like
cannot be detected.
20 [0006] The present invention has been made in view of
the foregoing, and it is an object of the present invention
to provide an inverter device capable of, with a simple
configuration, detecting an anomaly of a charging circuit
using a change in the resistance value of a limiting
25 resistor.
Solution to Problem
[0007] To solve the problem and achieve the object
described above, an aspect of the present invention
30 includes: a converter unit to convert an alternating
current voltage into a direct current voltage; a smoothing
capacitor to smooth the direct current voltage output by
the converter unit; an inverter unit to convert the direct
4
current voltage smoothed by the smoothing capacitor into an
alternating current voltage; a charging circuit connected
between the converter unit and the smoothing capacitor, the
charging circuit being a parallel circuit including a
5 limiting resistor and a contact element connected in
parallel with each other, the limiting resistor having a
positive temperature characteristic or having a
characteristic such that deterioration causes a resistance
value to increase, the contact element being controlled by
10 a contact signal such that the contact element is open or
short circuited; and a voltage detection unit to detect a
voltage across the smoothing capacitor, and output the
detected voltage as a voltage detection signal. An aspect
of present invention further includes a detection unit to
15 determine, based on the voltage detection signal, that the
resistance value of the limiting resistor is abnormal if a
voltage difference in the voltage across the smoothing
capacitor is greater than a reference value in a
predetermined time period that includes a time when the
20 contact signal is changed such that the contact element is
switched from open circuit to short circuit.
Advantageous Effects of Invention
[0008] An inverter device according to the present
25 invention has an effect where it is possible to, with a
simple configuration, detect an anomaly of a charging
circuit using a change in the resistance value of a
limiting resistor.
30 Brief Description of Drawings
[0009] FIG. 1 is a schematic configuration diagram of an
inverter device according to a first embodiment of the
present invention.
5
FIG. 2 is a flowchart of an initial charging operation
of the inverter device according to the first embodiment.
FIG. 3 is a time chart of the initial charging
operation of the inverter device when the charging circuit
5 is in a normal condition, according to the first embodiment.
FIG. 4 is a time chart of the initial charging
operation of the inverter device when the thermistor is in
an abnormal condition, according to the first embodiment.
FIG. 5 is a flowchart in a case in which the contact
10 element of the inverter device has an open fault, according
to a second embodiment of the present invention.
FIG. 6 is a time chart in a case in which the contact
element of the inverter device has an open fault, according
to the second embodiment.
15 FIG. 7 is a block diagram illustrating a configuration
of a microcomputer according to the first and the second
embodiments.
Description of Embodiments
20 [0010] An inverter device and an inverter device anomaly
detection method according to embodiments of the present
invention will be described in detail below with reference
to the drawings. Note that these embodiments are not
intended to limit this invention.
25 [0011] First Embodiment.
FIG. 1 is a schematic configuration diagram of an
inverter device 100 according to a first embodiment of the
present invention. In FIG. 1, a commercial AC power supply
1 is connected via a circuit breaker 2 to the inverter
30 device 100, and the inverter device 100 drives a motor 3.
When the circuit breaker 2 is open, an AC voltage from the
AC power supply 1 is not supplied to the inverter device
100, while when a signal input from a signal line (not
6
illustrated) causes the circuit breaker 2 to close, an AC
voltage from the AC power supply 1 is supplied to the
inverter device 100.
[0012] The inverter device 100 includes a converter unit
5 11 that performs full-wave rectification on the AC voltage
applied from the AC power supply 1 to convert the AC
voltage into a DC voltage; a smoothing capacitor 12
connected between DC buses 21 to smooth the DC voltage
output by the converter unit 11; and an inverter unit 13
10 connected between the DC buses 21 to convert the DC voltage
smoothed by the smoothing capacitor 12 into an AC voltage
having intended frequency and voltage. That is, the
inverter unit 13 converts the DC voltage across the
smoothing capacitor 12 that has been smoothed, into an AC
15 voltage. The DC buses 21 are power lines for applying a DC
voltage to the inverter unit 13. Herein, the inverter unit
13 consists of semiconductor switching elements such as
insulated gate bipolar transistors (IGBTs) and free
wheeling diodes. A specific example of the smoothing
20 capacitor 12 is an electrolytic capacitor.
[0013] The inverter device 100 further includes a
charging circuit 20 connected between the converter unit 11
and the smoothing capacitor 12 to perform initial charging
of the smoothing capacitor 12. The charging circuit 20 is
25 a parallel circuit that includes a thermistor 14, serving
as a limiting resistor, and a contact element 15 connected
in parallel with each other. The thermistor 14 has a
positive temperature characteristic. A positive
temperature characteristic refers to a characteristic where
30 a temperature rise causes an increase in the resistance
value. The thermistor 14 is a current limiting element
connected between the converter unit 11 and the smoothing
capacitor 12 to limit the initial charge current to the
7
smoothing capacitor 12. The contact element 15 is an
element that can be either in an open circuit or short
circuit state, and is implemented by a relay or the like.
The contact element 15 is connected in parallel with the
5 thermistor 14, and can short-circuit across the thermistor
14. The thermistor 14 is not particularly limited as long
as the thermistor 14 is a limiting resistor having an
impedance component to limit an inrush current, and has a
positive temperature characteristic. In addition, as long
10 as the thermistor 14 as a whole has a positive temperature
characteristic, the thermistor 14 may be any one of a
single limiting resistor, a set of multiple limiting
resistors connected in parallel with one another, a set of
multiple limiting resistors connected in series with one
15 another, and a set of multiple limiting resistors connected
with a combination of series and parallel connections.
[0014] The inverter device 100 further includes a
voltage detection unit 16 that detects the DC voltage
across the smoothing capacitor 12; a charging circuit
20 anomaly detection unit 17 that is a detection unit that
outputs an anomaly detection signal; an inverter control
unit 18 that outputs a pulse width modulation (PWM) signal
to the inverter unit 13; and a display unit 19 that
displays anomaly information.
25 [0015] The voltage detection unit 16 detects a DC
voltage that is the voltage across the smoothing capacitor
12, and outputs information on the detected voltage across
the smoothing capacitor 12 to the charging circuit anomaly
detection unit 17 and to the inverter control unit 18 as a
30 voltage detection signal. Note that the voltage detection
unit 16 is typically included in the inverter device 100
for breakdown protection of the smoothing capacitor 12
and/or the like.
8
[0016] The charging circuit anomaly detection unit 17
detects an anomaly of the charging circuit 20, and sends a
relay signal, which is a contact signal, to the contact
element 15, and thus can control whether the contact
5 element 15 is open or short circuited. The contact signal
can have either a value representing an OFF state or a
value representing an ON state. The contact signal is
hereinafter referred to as being in an ON state if the
contact signal has a value representing an ON state, and as
10 being in an OFF state if the contact signal has a value
representing an OFF state. A contact signal in an ON state
causes the contact element 15 to be controlled such that it
is short circuited, while a contact signal in an OFF state
causes the contact element 15 to be controlled such that it
15 is open. Upon power-on of the inverter device 100, the
charging circuit anomaly detection unit 17 calculates the
voltage difference between the voltage across the smoothing
capacitor 12 immediately before the contact signal is
switched from OFF state to ON state, and the voltage across
20 the smoothing capacitor 12 immediately after the contact
signal is switched to the ON state, on the basis of the
voltage detection signal from the voltage detection unit 16.
The charging circuit anomaly detection unit 17 can detect
from the calculated voltage difference that the resistance
25 value of the thermistor 14 has changed to an abnormal value.
Thus, the charging circuit anomaly detection unit 17
determines a temperature anomaly of the thermistor 14. The
charging circuit anomaly detection unit 17 can further
detect an open fault of the contact element 15 on the basis
30 of the variation of the voltage detection signal provided
from the voltage detection unit 16. Upon determination of
the existence of an anomaly of the resistance value of the
thermistor 14 and upon detection of an open fault of the
9
contact element 15, the charging circuit anomaly detection
unit 17 outputs an anomaly detection signal to the inverter
control unit 18 and to the display unit 19.
[0017] The inverter control unit 18 calculates a voltage
5 instruction signal on the basis of a frequency instruction
value from a frequency setter (not illustrated), performs
an operation to compare the voltage instruction signal with
a carrier frequency signal to generate a PWM signal, which
is a control signal, and outputs the PWM signal to the
10 inverter unit 13. The PWM signal is a signal for
controlling whether each of the semiconductor switching
elements included in the inverter unit 13 is in an ON state
or in an OFF state.
[0018] The display unit 19 displays anomaly information
15 on the basis of the anomaly detection signal that is output
when the charging circuit anomaly detection unit 17 detects
an anomaly.
[0019] FIG. 2 is a flowchart of an initial charging
operation of the inverter device 100 according to the first
20 embodiment. FIG. 2 illustrates an initial charging
operation during which the contact signal transitions to an
ON state before a charge process of the smoothing capacitor
12 completes. FIG. 3 is a time chart of the initial
charging operation of the inverter device 100 when the
25 charging circuit 20 according to the first embodiment is in
a normal condition. As used herein, the phrase “the
charging circuit 20 is in a normal condition” means that
the thermistor 14 and the contact element 15 are both in a
normal condition. The initial charging operation will be
30 described below for a case in which the charging circuit 20
is in a normal condition referring to FIGS. 2 and 3.
[0020] (Initial charging operation when charging circuit
20 is in normal condition)
10
To start up the inverter device 100, at time t0, a
signal is input from a signal line (not illustrated) to
close the circuit breaker 2, causing an AC voltage to be
applied from the AC power supply 1 to the converter unit 11
5 (step S11). The AC voltage applied is rectified by the
converter unit 11 to initiate the initial charging of the
smoothing capacitor 12. In this situation, because the
contact element 15 is open, a charge current that is
controlled using the thermistor 14 flows into the smoothing
10 capacitor 12. Then, the level of the voltage detection
signal representing the voltage across the smoothing
capacitor 12 increases in accordance with the time constant
dependent on the resistance of the thermistor 14 and on the
capacitance of the smoothing capacitor 12.
15 [0021] At time t1, the level of the voltage detection
signal reaches a predetermined voltage V1 (step S12). The
voltage V1 is previously determined based on the AC voltage
value of the AC power supply 1 or the like. Then, the
voltage detection unit 16 detects a voltage V2, which is
20 the voltage across the smoothing capacitor 12 at time t2,
which is immediately before the contact signal to the
contact element 15 is switched from OFF state to ON state
by the charging circuit anomaly detection unit 17 (step
S13), and outputs information on the voltage V2 as the
25 voltage detection signal. Upon reception of the voltage
detection signal representing the voltage V2, the charging
circuit anomaly detection unit 17 stores the value of the
voltage V2. Time t2 is immediately before time t3, and at
time t3, the contact signal is switched from OFF state to
30 ON state. Time t3 is a time when a predetermined time T1
has elapsed since time t1. In addition, the time period
from time t2 to time t3 is previously determined. At time
t3, the charging circuit anomaly detection unit 17 switches
11
the contact signal from OFF state to ON state (step S14).
Transition of the contact signal to the ON state shortcircuits the contact element 15, causing the charge current
to increase, and thus causing the voltage across the
5 smoothing capacitor 12 to increase to a voltage V3.
[0022] Then, the voltage detection unit 16 detects the
voltage V3, which is the voltage across the smoothing
capacitor 12 at time t4, which is immediately after the
contact signal to the contact element 15 is switched from
10 OFF state to ON state by the charging circuit anomaly
detection unit 17 (step S15), and outputs information on
the voltage V3 as the voltage detection signal. Upon
reception of the voltage detection signal representing the
voltage V3, the charging circuit anomaly detection unit 17
15 stores the value of the voltage V3. Time t4 is immediately
after time t3, and the time period from time t3 to time t4
is previously determined. Thus, the time period from time
t2 to time t4 is a predetermined time period.
[0023] The charging circuit anomaly detection unit 17
20 calculates a voltage difference V3-V2 between time t2 and
time t4 in the voltage across the smoothing capacitor 12,
and determines whether the voltage difference is less than
or equal to a predefined reference value (step S16). If
the charging circuit anomaly detection unit 17 determines
25 that the voltage difference is less than or equal to the
reference value (step S16: Yes), the charging circuit
anomaly detection unit 17 determines that the thermistor 14
is in a normal condition, and therefore does not output an
anomaly detection signal. Thus, the inverter control unit
30 18 does not receive an anomaly detection signal, and
accordingly, outputs a PWM signal when an operation signal
is input (step S17).
[0024] FIG. 4 is a time chart of the initial charging
12
operation of the inverter device 100 when the thermistor 14
according to the first embodiment is in an abnormal
condition. As used herein, the phrase “the thermistor 14
is in an abnormal condition” specifically means that
5 current heating due to power-on of the AC power supply 1 at
step S11 or an effect of an ambient environment has caused
the temperature of the thermistor 14 having a positive
temperature characteristic to increase, thereby causing the
resistance value to exceed a predicted value to become an
10 abnormal value. The initial charging operation will be
described below for a case in which thermistor 14 is in an
abnormal condition referring to FIGS. 2 and 4.
[0025] (Initial charging operation when thermistor 14 is
in abnormal condition)
15 Upon beginning of the initial charging of the
smoothing capacitor 12 at step S11, if the resistance value
of the thermistor 14 is higher than a predicted value due
to the foregoing cause, the time constant dependent on the
resistance of the thermistor 14 and on the capacitance of
20 the smoothing capacitor 12 becomes much higher than the
time constant when the thermistor 14 is in a normal
condition. As a result, as illustrated in FIG. 4, the
voltage increase of the smoothing capacitor 12 is smaller
than the voltage increase in the case of FIG. 3 in which
25 the thermistor 14 is in a normal condition.
[0026] At time t11, the voltage across the smoothing
capacitor 12 reaches the predetermined voltage V1 (step
S12). Then, the voltage detection unit 16 detects a
voltage V21, which is the voltage across the smoothing
30 capacitor 12 at time t21, which is immediately before the
contact signal to the contact element 15 is switched from
OFF state to ON state by the charging circuit anomaly
detection unit 17 (step S13), and outputs information on
13
the voltage V21 as the voltage detection signal. Upon
reception of the voltage detection signal representing the
voltage V21, the charging circuit anomaly detection unit 17
stores the value of the voltage V21. Time t21 is
5 immediately before time t31, and at time t31, the contact
signal is switched from OFF state to ON state. Time t31 is
a time when the predetermined time T1 has elapsed since
time t11. In addition, the time period from time t21 to
time t31 is the same as the time period from time t2 to
10 time t3 of FIG. 3. At time t31, the charging circuit
anomaly detection unit 17 switches the contact signal from
OFF state to ON state (step S14). Transition of the
contact signal to the ON state short-circuits the contact
element 15, causing the charge current to increase, and
15 thus causing the voltage across the smoothing capacitor 12
to increase to the voltage V3.
[0027] Then, the voltage detection unit 16 detects the
voltage V3, which is the voltage across the smoothing
capacitor 12 at time t41, which is immediately after the
20 contact signal to the contact element 15 is switched from
OFF state to ON state by the charging circuit anomaly
detection unit 17 (step S15), and outputs information on
the voltage V3 as the voltage detection signal. Upon
reception of the voltage detection signal representing the
25 voltage V3, the charging circuit anomaly detection unit 17
stores the value of the voltage V3. Time t41 is
immediately after time t31, and the time period from time
t31 to time t41 is the same as the time period from time t3
to time t4 of FIG. 3. Therefore, the time period from time
30 t21 to time t41 is the same time period as the time period
from time t2 to time t4 of FIG. 3.
[0028] As described above, because the increase in the
voltage across the smoothing capacitor 12 from time t11 of
14
FIG. 4 is smaller than the increase in the voltage across
the smoothing capacitor 12 from time t1 of FIG. 3, the
voltage V21 is lower than the voltage V2 of FIG. 3 when the
thermistor 14 is in a normal condition. Meanwhile, the
5 voltage V3 is the voltage across the smoothing capacitor 12
when the contact element 15 is short-circuited, and thus
remains unchanged from when the thermistor 14 is in a
normal condition. Therefore, the voltage difference V3-V21
during the time period from time t21 to time t41 in the
10 voltage across the smoothing capacitor 12 is greater than
the voltage difference V3-V2 during the time period from
time t2 to time t4 of FIG. 3 in the voltage across the
smoothing capacitor 12. Thus, the charging circuit anomaly
detection unit 17 calculates the voltage difference V3-V21
15 to determine whether the voltage difference is less than or
equal to a reference value (step S16). If the charging
circuit anomaly detection unit 17 determines that the
voltage difference is greater than the reference value
(step S16: No), the charging circuit anomaly detection unit
20 17 determines that the resistance value of the thermistor
14 is abnormal, and thus outputs an anomaly detection
signal (step S18). As a result, having received the
anomaly detection signal, the inverter control unit 18 does
not output a PWM signal to the inverter unit 13 even when
25 an operation signal is received. In addition, the display
unit 19 that have received the anomaly detection signal can
display information indicating that the resistance value of
the thermistor 14 is abnormal.
[0029] As described above, by using the thermistor 14
30 having a positive temperature characteristic as a limiting
resistor of the charging circuit 20, current heating or an
abnormal ambient environment, such as an increase in
ambient temperature, results in an abnormally high
15
resistance value of the thermistor 14. Thus, the voltage
difference V3-V21 exceeds the predefined reference value,
thereby enabling the charging circuit anomaly detection
unit 17 to determine that the temperature of the thermistor
5 14 or the ambient temperature is abnormal.
[0030] Even when the input supply voltage varies
depending on the environment of the AC power supply 1, and
such variation causes the value of the voltage V3 to vary
or the rising edge shape of the voltage across the
10 smoothing capacitor 12 after power-on to vary, an anomaly
of the resistance value of the thermistor 14 causes the
voltage difference in the voltage across the smoothing
capacitor 12 between before and after the contact signal is
switched from OFF state to ON state to exceed a reference
15 value. Thus, determination of the existence of an anomaly
in the resistance value of the thermistor 14 based on this
voltage difference enables an anomaly of the thermistor 14
to be detected irrespective of the input supply voltage.
[0031] Note that the foregoing description has described
20 that a check is made for an increase in the resistance
value due to an increase of the temperature of the
thermistor 14 caused by power-on of the AC power supply 1
or by an ambient temperature increase by using the
thermistor 14 having a positive temperature characteristic
25 as the limiting resistor of the charging circuit 20, but
the inverter device 100 according to the first embodiment
can also check the resistance value itself of the limiting
resistor of the charging circuit 20 for an anomaly.
[0032] If a general resistor is used as the limiting
30 resistor, deterioration of the resistor may cause an
increase in the resistance value. That is, as the limiting
resistor of the charging circuit 20, a resistor may be used
that has a characteristic such that deterioration causes
16
the resistance value to increase. Also in this case, an
increase in the resistance value of the limiting resistor
causes the voltage difference, between before and after the
contact signal is switched from OFF state to ON state, in
5 the voltage across the smoothing capacitor 12 to exceed the
reference value, thereby enabling a check to be made for an
anomaly of the resistance value of the limiting resistor.
[0033] In addition, the inverter device 100 may include
a circuit that switches the contact signal to the ON state
10 after it is determined that the voltage across the
smoothing capacitor 12 is saturated by measuring the
voltage detection signal output from the voltage detection
unit 16 at appropriate time intervals. Even in such an
inverter device 100, the voltage difference dependent on
15 the input current to the power circuit that supplies power
to a control circuit usually included, to the display unit
19, and to other similar component, and on the resistance
value that is now an excess value caused by an increase in
the temperature of the thermistor 14 having a positive
20 temperature characteristic, can be detected as the voltage
difference between before and after the contact signal to
the contact element 15 is switched from OFF state to ON
state. Therefore, an anomaly of the resistance value can
be similarly detected.
25 [0034] As described above, the inverter device 100
according to the first embodiment can detect, with a simple
configuration, an anomaly of the charging circuit 20 using
a change in the resistance value of the limiting resistor
by using the voltage detection unit 16 usually included for
30 breakdown protection of the smoothing capacitor 12 and/or
the like. Thus, an increase in cost and an increase in the
size of the apparatus can be reduced or prevented.
[0035] Second Embodiment.
17
The inverter device 100 according to a second
embodiment has the same configuration as the configuration
illustrated in FIG. 1. FIG. 5 is a flowchart in a case in
which the contact element 15 of the inverter device 100
5 according to the second embodiment of the present invention
has an open fault. FIG. 6 is a time chart in a case in
which the contact element 15 of the inverter device 100
according to the second embodiment has an open fault. An
operation of the inverter device 100 when the contact
10 element 15 has an open fault will be described below
referring to FIGS. 5 and 6.
[0036] (Operation of inverter device 100 when contact
element 15 has an open fault)
To start up the inverter device 100, at time t0, the
15 circuit breaker 2 is closed to apply an AC voltage to the
converter unit 11 (step S21). The AC voltage applied is
rectified by the converter unit 11 to initiate the initial
charging of the smoothing capacitor 12. In this situation,
because the contact element 15 is open, a charge current
20 that is controlled using the thermistor 14 flows into the
smoothing capacitor 12. Then, the level of the voltage
detection signal representing the voltage across the
smoothing capacitor 12 increases in accordance with the
time constant dependent on the resistance of the thermistor
25 14 and on the capacitance of the smoothing capacitor 12.
[0037] At time t12, the level of the voltage detection
signal reaches the predetermined voltage V1 (step S22).
Then, the charging circuit anomaly detection unit 17
switches the contact signal from OFF state to ON state at
30 time t32, that is, after the predetermined time T1 has
elapsed since time t12 (step S23). If the contact element
15 has an open fault due to some cause, the contact element
15 that has received a contact signal representing the ON
18
state still maintains the open state. Then, reception of
an operation signal causes the inverter control unit 18 to
output a PWM signal, thereby causing a current to the motor
3 to continuously flow through the thermistor 14. Thus,
5 the temperature of the thermistor 14 having a positive
temperature characteristic increases.
[0038] An increase in the temperature of the thermistor
14 causes the resistance value to increase, thereby
preventing a current from flowing to the smoothing
10 capacitor 12 from an outlet portion of the converter unit
11. Thus, the voltage across the smoothing capacitor 12
represented by the voltage detection signal gradually
decreases (step S24). When the voltage across the
smoothing capacitor 12 represented by the voltage detection
15 signal decreases to less than or equal to a voltage V32,
which is a predetermined first threshold illustrated in FIG.
6, the inverter control unit 18 stops outputting the PWM
signal (step S25), and outputs an alarm to the display unit
19. The display unit 19 can display alarm information
20 indicating that the outputting of the PWM signal is stopped.
The PWM signal stoppage prevents a current from flowing to
the motor 3, and as a result, the current flowing through
the thermistor 14 to drive the motor 3 is no more output,
thereby resulting in a decrease in the amount of electrical
25 current.
[0039] A decrease in the amount of electrical current
flowing through the thermistor 14 allows heat of the
thermistor 14 to dissipate into air to lower the
temperature of the thermistor 14, thereby allowing the
30 resistance value of the thermistor 14 to begin to decrease
toward a desirable value. This then increases the current
to the smoothing capacitor 12, thereby causing the voltage
across the smoothing capacitor 12 represented by the
19
voltage detection signal to gradually increase (step S26).
When the voltage across the smoothing capacitor 12
represented by the voltage detection signal increases, and
reaches or exceeds a voltage V33 illustrated in FIG. 6,
5 which is a predetermined second threshold defined as a
voltage value higher than the first threshold, the inverter
control unit 18 starts again to output the PWM signal (step
S27), and stops outputting the alarm to cause the display
unit 19 not to display alarm information any more. The PWM
10 signal stoppage at step S25 and the PWM signal output
operation at step S27 are repeated until the charging
circuit anomaly detection unit 17 determines that the
contact element 15 has an open fault as described below.
[0040] The charging circuit anomaly detection unit 17
15 determines, based on the voltage detection signal, whether
the number of iterations of the PWM signal stoppage and the
PWM signal output operation reaches or exceeds a
predetermined specific number of times within a
predetermined specific time period (step S28).
20 Specifically, the charging circuit anomaly detection unit
17 makes a determination of step S28 as to whether the
number of times the voltage across the smoothing capacitor
12 reaches or exceeds the voltage V33 after reaching or
falling below the voltage V32 reaches or exceeds a specific
25 number of times within a specific time period, on the basis
of the voltage detection signal provided by the voltage
detection unit 16. If the charging circuit anomaly
detection unit 17 determines that the specific time period
has not yet elapsed since the PWM signal output operation
30 has been initiated, or determines that the number of
iterations of the PWM signal stoppage and the PWM signal
output operation in the specific time period is less than
the specific number of times (step S28: No), the process
20
returns to step S24. Otherwise, if the charging circuit
anomaly detection unit 17 determines that the number of
iterations of the PWM signal stoppage and the PWM signal
output operation in the specific time period is greater
5 than or equal to the specific number of times (step S28:
Yes), the charging circuit anomaly detection unit 17
determines that an anomaly has occurred in which the
contact element 15 has an open fault, and thus outputs an
anomaly detection signal (step S29). As a result, having
10 received the anomaly detection signal, the inverter control
unit 18 does not output a PWM signal to the inverter unit
13 even when an operation signal is received. In addition,
the display unit 19 that have received the anomaly
detection signal can display information indicating that
15 the contact element 15 has an open fault. As described
above, the inverter device 100 according to the second
embodiment can detect an open fault of the contact element
15 after completion of charging the smoothing capacitor 12
using a change in the resistance value of the limiting
20 resistor. Thus, an anomaly of the charging circuit 20 can
be detected with a simple configuration.
[0041] As a method for determining that the contact
element has an open fault, Patent Literature 1 describes a
method that determines that an open fault has occurred in
25 the contact element on the basis of the behavior of the
voltage across an electrolytic capacitor during the initial
charging process immediately after power-on. However, the
determination on a fault of the contact element is made
during the initial charging process immediately after
30 power-on, and thus, this poses a problem in that if an open
fault of the contact element occurs after completion of
charging, such open fault cannot be detected, thereby
allowing the PWM signal output operation to be continued.
21
In contrast, the inverter device 100 according to the
second embodiment is capable of detecting an open fault
after completion of charging, and can thus detect an open
fault of the contact element 15 and stop outputting the PWM
5 signal even when an open fault of the contact element 15
occurs after completion of charging.
[0042] Moreover, another example of method for
determining that the contact element has an open fault is a
method that makes a determination by disposing a
10 temperature detection element in the vicinity of the
thermistor that serves as a limiting resistor.
Specifically, if the contact element has an open fault,
heat generation by the thermistor due to a continuous flow,
through the thermistor, of a current that flows to the
15 motor is detected using the temperature detection element.
That is, it is determined that the contact element has an
open fault if the temperature detected reaches or exceeds a
predetermined temperature. However, the method described
above requires addition of a temperature detection element
20 and a temperature detection circuit, thereby posing a
problem of increase in cost and in installation area. In
contrast, the inverter device 100 according to the second
embodiment requires no additional temperature detection
element as described above, and can thus be implemented
25 with a simple configuration using the voltage detection
unit 16 that is usually included.
[0043] Note that the above description of the second
embodiment has only described the operation required for
the charging circuit anomaly detection unit 17 to detect an
30 open fault of the contact element 15. However, the
operation for determining the existence of an anomaly of
the resistance value of the thermistor 14 according to the
first embodiment and the operation for detecting an open
22
fault may both be performed. In such a case, the process
proceeds to step S24 of FIG. 5 after step S17 of FIG. 2.
That is, if the charging circuit anomaly detection unit 17
determines that the thermistor 14 is in a normal condition,
5 it is then determined whether there is an open fault of the
contact element 15. In addition, if these operations are
both performed, the anomaly detection signal that is output
at step S18 of FIG. 2 by the charging circuit anomaly
detection unit 17 that has determined that the resistance
10 value of the thermistor 14 is abnormal, and the anomaly
detection signal that is output at step S29 of FIG. 5 by
the charging circuit anomaly detection unit 17 that has
determined that the contact element 15 has an open fault
have different signal contents, types, and/or the like to
15 make both anomaly detection signals distinguishable from
each other.
[0044] The charging circuit anomaly detection unit 17
and the inverter control unit 18 according to the first and
the second embodiments are specifically implemented in a
20 microcomputer or the like. FIG. 7 is a block diagram
illustrating a configuration of a microcomputer 200
according to the first and the second embodiments. The
functions of the charging circuit anomaly detection unit 17
and of the inverter control unit 18 are provided by the
25 microcomputer 200 having a configuration such as one
illustrated in FIG. 7. The microcomputer 200 includes a
central processing unit (CPU) 201 that performs operations
and control; a random access memory (RAM) 202 used by the
CPU 201 as a work area; a read-only memory (ROM) 203 that
30 stores programs and data; an input/output (I/O) device 204,
which is hardware for exchanging signals with external
devices; and a peripheral device 205 including an
oscillator that generates a clock signal. The anomaly
23
detection method performed by the charging circuit anomaly
detection unit 17, and the inverter control method
performed by the inverter control unit 18 described above
are performed by the CPU 201 executing a program stored in
5 the ROM 203. Note that the charging circuit anomaly
detection unit 17 may be implemented in a dedicated circuit
instead of in the microcomputer 200.
[0045] As described above, the inverter device 100
causes the voltage detection unit 16 to detect the voltages
10 before and after the contact signal to the contact element
15 is changed from OFF state to ON state during the initial
charging of the smoothing capacitor 12 to obtain the
voltage difference therebetween, and can thus detect, from
this voltage difference, an anomaly of the resistance value
15 of the thermistor 14. In addition, monitoring the number
of iterations of the PWM signal stoppage and output
operation while a PWM signal is output in the inverter
device 100 enables an open fault of the contact element 15
to be detected. This can prevent a secondary failure
20 induced by a fault of the charging circuit 20.
[0046] The method for detecting a change in the time
constant of the voltage across the electrolytic capacitor
in a charge process due to a change in the resistance value
of the limiting resistor may be such that a voltage
25 detection unit for measuring the voltage across the
electrolytic capacitor and a current detection unit for
measuring the inrush current are installed, and a change in
the time constant is computed from the voltage and the
current detected. Such a voltage detection unit is usually
30 included in the inverter device to provide control or
overvoltage protection of the electrolytic capacitor, while,
in contrast, providing the above-mentioned current
detection unit requires an addition of a circuit. In
24
addition, the above-mentioned current detection unit needs
to be included in the main circuit portion that supplies
current to the motor while the inverter device is in a
normal operation. This poses a problem in that the current
5 detection element in the current detection unit is
increased in size, thereby increasing the cost and the
installation area. In contrast, the inverter device 100
according to the first and the second embodiments does not
require the above-mentioned current detection unit, and can
10 thus be implemented with a simple configuration using a
voltage detection unit usually included.
[0047] In addition, a determination may be made such
that the limiting resistor of the charging circuit is in a
normal condition if the voltage across the electrolytic
15 capacitor reaches a predetermined voltage. However, the
input voltage applied to the inverter device may vary
within a wide tolerance range of about ±20%, which poses a
problem in that the method for determining the existence of
an anomaly of the voltage across the electrolytic capacitor
20 using a predetermined voltage may lead to a false
determination of whether the limiting resistor of the
charging circuit is normal or abnormal. In this regard,
the inverter device 100 according to the first embodiment
determines whether the limiting resistor of the charging
25 circuit is in a normal condition on the basis of the
voltage difference, between immediately before and
immediately after the contact signal is switched from OFF
state to ON state, in the voltage across the smoothing
capacitor 12 after power-on, and can thus determine the
30 state of the charging circuit irrespective of the input
voltage.
[0048] The configurations described in the foregoing
embodiments are merely examples of various aspects of the
25
present invention. These configurations may be combined
with other known technologies, and moreover, a part of such
configurations may be omitted and/or modified without
departing from the spirit of the present invention.
5
Reference Signs List
[0049] 1 AC power supply; 2 circuit breaker; 3 motor;
11 converter unit; 12 smoothing capacitor; 13 inverter
unit; 14 thermistor; 15 contact element; 16 voltage
10 detection unit; 17 charging circuit anomaly detection
unit; 18 inverter control unit; 19 display unit; 20
charging circuit; 21 DC bus; 100 inverter device; 200
microcomputer; 201 CPU; 202 RAM; 203 ROM; 204 I/O
device; 205 peripheral device.
15
26
We Claim:
1. An inverter device comprising:
a converter unit to convert an alternating current
5 voltage into a direct current voltage;
a smoothing capacitor to smooth the direct current
voltage output by the converter unit;
an inverter unit to convert the direct current voltage
smoothed by the smoothing capacitor into an alternating
10 current voltage;
a charging circuit connected between the converter
unit and the smoothing capacitor, the charging circuit
being a parallel circuit including a limiting resistor and
a contact element connected in parallel with each other,
15 the limiting resistor having a positive temperature
characteristic or having a characteristic such that
deterioration causes a resistance value to increase, the
contact element being controlled by a contact signal such
that the contact element is open or short circuited;
20 a voltage detection unit to detect a voltage across
the smoothing capacitor, and output the detected voltage as
a voltage detection signal; and
a detection unit to determine, based on the voltage
detection signal, that the resistance value of the limiting
25 resistor is abnormal if a voltage difference in the voltage
across the smoothing capacitor is greater than a reference
value in a predetermined time period that includes a time
when the contact signal is changed such that the contact
element is switched from open circuit to short circuit.
30
2. An inverter device comprising:
a converter unit to convert an alternating current
voltage into a direct current voltage;
27
a smoothing capacitor to smooth the direct current
voltage output by the converter unit;
an inverter unit to convert the direct current voltage
smoothed by the smoothing capacitor into an alternating
5 current voltage;
a charging circuit connected between the converter
unit and the smoothing capacitor, the charging circuit
being a parallel circuit including a limiting resistor and
a contact element connected in parallel with each other,
10 the limiting resistor having a positive temperature
characteristic, the contact element being controlled by a
contact signal such that the contact element is open or
short circuited;
a voltage detection unit to detect a voltage across
15 the smoothing capacitor, and output the detected voltage as
a voltage detection signal; and
a detection unit to determine, based on the voltage
detection signal, that the contact element is in an
abnormal condition due to an occurrence of an open fault if
20 the number of times the voltage across the smoothing
capacitor reaches or exceeds a second threshold, which is a
voltage value higher than a first threshold, after reaching
or falling below the first threshold, reaches or exceeds a
specific number of times within a specific time period.
25
3. The inverter device according to claim 1 or 2,
comprising:
an inverter control unit to generate a control signal
for controlling the inverter unit, wherein
30 if the detection unit determines that the resistance
value of the limiting resistor is abnormal or that the
contact element is in an abnormal condition, the inverter
control unit does not output the control signal to the
28
inverter unit.
4. An inverter device anomaly detection method, in an
inverter device that includes a converter unit to convert
5 an alternating current voltage into a direct current
voltage; a smoothing capacitor to smooth the direct current
voltage output by the converter unit; an inverter unit to
convert the direct current voltage smoothed by the
smoothing capacitor into an alternating current voltage; a
10 charging circuit connected between the converter unit and
the smoothing capacitor, the charging circuit being a
parallel circuit including a limiting resistor and a
contact element connected in parallel with each other, the
limiting resistor having a positive temperature
15 characteristic or having a characteristic such that
deterioration causes a resistance value to increase, the
contact element being controlled by a contact signal such
that the contact element is open or short circuited; and a
voltage detection unit to detect a voltage across the
20 smoothing capacitor, and output the detected voltage as a
voltage detection signal, the method comprising:
a step of determining, based on the voltage detection
signal, whether a voltage difference in the voltage across
the smoothing capacitor is less than or equal to a
25 reference value in a predetermined time period that
includes a time when the contact signal is changed such
that the contact element is switched from open circuit to
short circuit; and
a step of, if the voltage difference is greater than
30 the reference value, determining that the resistance value
of the limiting resistor is abnormal.
5. An inverter device anomaly detection method, in an
29
inverter device that includes a converter unit to convert
an alternating current voltage into a direct current
voltage; a smoothing capacitor to smooth the direct current
voltage output by the converter unit; an inverter unit to
5 convert the direct current voltage smoothed by the
smoothing capacitor into an alternating current voltage; a
charging circuit connected between the converter unit and
the smoothing capacitor, the charging circuit being a
parallel circuit including a limiting resistor and a
10 contact element connected in parallel with each other, the
limiting resistor having a positive temperature
characteristic, the contact element being controlled by a
contact signal such that the contact element is open or
short circuited; and a voltage detection unit to detect a
15 voltage across the smoothing capacitor, and output the
detected voltage as a voltage detection signal, the method
comprising:
a step of determining whether the number of times the
voltage across the smoothing capacitor reaches or exceeds a
20 second threshold, which is a voltage value higher than a
first threshold, after reaching or falling below the first
threshold, reaches or exceeds a specific number of times
within a specific time period; and
a step of, if the number of times reaches or exceeds
25 the specific number of times within the specific time
period, determining that the contact element is in an
abnormal condition due to an occurrence of an open fault.
6. The inverter device anomaly detection method according
30 to claim 4 or 5, wherein
the inverter device includes an inverter control unit
to generate a control signal for controlling the inverter
unit, and
30
if it is determined that the resistance value of the
limiting resistor is abnormal or that the contact element
is in an abnormal condition, the inverter device causes the
inverter control unit not to output the control signal to
5 the inverter unit.