FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
MOTOR DRIVE DEVICE AND REFRIGERATION CYCLE APPARATUS
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
Field
[0001] The present disclosure relates to a motor drive
device that includes a power converter for converting input
5 AC power into desired power to a motor and drives the motor,
and a refrigeration cycle apparatus.
Background
[0002] Using a large-capacitance capacitor generally
10 leads to increases in the size and cost of power converters.
There have been known power converters intended to reduce
the capacitance of a capacitor of a smoothing unit provided
between a converter and an inverter.
[0003] For example, the following Patent Literature
15 discloses a technique of providing a phase difference between
a carrier for converter-side pulse width modulation (PWM)
control and a carrier for inverter-side PWM control, and
adjusting the phase difference to maximize an area where
both pulses coincide with each other. Patent Literature 1
20 describes that current flowing through the capacitor of the
smoothing unit can be minimized, so that the capacitance of
the capacitor of the smoothing unit is minimized.
Citation List
25 Patent Literature
[0004] Patent Literature 1: Japanese Patent Application
Laid-open No. 2006-288035
Summary of Invention
30 Problem to be solved by the Invention
[0005] However, as a characteristic of motor drive
devices, it is necessary to increase inverter current flowing
through the inverter in a high load range where the load on
3
the motor is large. In such a high load range, current
flowing from the capacitor of the smoothing unit also
inevitably increases, so that it is difficult to minimize
current flowing through the capacitor of the smoothing unit.
5 Therefore, when a small-capacitance capacitor is used, a
problem such as a failure of the capacitor due to a
temperature rise may occur particularly under a high outside
temperature environment where the outside temperature is
high.
10 [0006] As described above, the technique of Patent
Literature 1 has difficulty in driving in the high load range
and under the high outside temperature environment, and has
a problem that the reliability of the device decreases when
a small-capacitance capacitor is used.
15 [0007] The present disclosure has been made in view of
the above. It is an object of the present disclosure to
provide a motor drive device that can prevent a decrease in
the reliability of the unit even in driving in the high load
range and under the high outside temperature environment.
20
Means to Solve the Problem
[0008] To solve the above-described problem and achieve
the object, a motor drive device according to the present
disclosure includes a rectifier unit, a capacitor connected
25 to an output end of the rectifier unit, an inverter connected
across the capacitor, and a control unit. The rectifier
unit rectifies first AC power supplied from a commercial
power supply. The inverter generates second AC power and
outputs the second AC power to a motor. The control unit
30 controls the operation of the inverter such that pulsation
according to the power state of the capacitor is superimposed
on a drive pattern of the motor, to reduce a charge and
discharge current of the capacitor. The control unit
4
performs load pulsation compensation control to compensate
for load pulsation, power supply pulsation compensation
control to reduce the charge and discharge current of the
capacitor, and overload compensation control to reduce an
5 inverter input current input to the inverter, while
preferentially performing constant current load control to
control the rotational speed of the motor.
Effects of the Invention
10 [0009] The motor drive device according to the present
disclosure achieves the effect of being able to prevent a
decrease in the reliability of the unit even in driving in
the high load range and under the high outside temperature
environment.
15
Brief Description of Drawings
[0010] FIG. 1 is a diagram illustrating an exemplary
configuration of a motor drive device according to a first
embodiment.
20 FIG. 2 is a diagram illustrating an exemplary
configuration in which the motor drive device according to
the first embodiment is applied to a refrigeration cycle
apparatus.
FIG. 3 is a diagram for explaining torque of a rotary
25 compressor and a reciprocating compressor that are examples
of a compressor included in the refrigeration cycle apparatus
illustrated in FIG. 2.
FIG. 4 is a block diagram illustrating an exemplary
configuration of a control unit included in the motor drive
30 device according to the first embodiment.
FIG. 5 is a flowchart for explaining the operations of
principal components in the control unit included in the
motor drive device according to the first embodiment.
5
FIG. 6 is a diagram illustrating an example of a
hardware configuration that implements the control unit
included in the motor drive device according to the first
embodiment.
5
Description of Embodiments
[0011] Hereinafter, a motor drive device and a
refrigeration cycle apparatus according to embodiments of
the present disclosure will be described in detail with
10 reference to the accompanying drawings. Note that the
embodiments described below are exemplifications, and the
scope of the present disclosure is not limited by the
following embodiments.
[0012] First Embodiment.
15 FIG. 1 is a diagram illustrating an exemplary
configuration of a motor drive device according to a first
embodiment. In FIG. 1, a motor drive device 10 according to
the first embodiment is connected to a commercial power
supply 1 and a compressor 30. The motor drive device 10
20 converts first AC power supplied from the commercial power
supply 1 into second AC power having a desired amplitude and
desired phases, and supplies the second AC power to the
compressor 30. The commercial power supply 1 is an example
of an AC source. A motor 32 is installed in the compressor
25 30. An example of the motor 32 is a sensorless brushless
motor.
[0013] The motor drive device 10 includes a reactor 2, a
rectifier unit 3, a smoothing unit 4, an inverter 5, a
control unit 6, and current detection units 7 and 8.
30 [0014] The reactor 2 is connected between the commercial
power supply 1 and the rectifier unit 3. The rectifier unit
3 includes a bridge circuit composed of four rectifier
elements, and rectifies the first AC power supplied from the
6
commercial power supply 1 for output. The rectifier unit 3
performs full-wave rectification.
[0015] The smoothing unit 4 is connected to an output end
of the rectifier unit 3. The smoothing unit 4 includes a
5 capacitor 4a as a smoothing element, and smooths the power
rectified by the rectifier unit 3. The capacitor 4a is, for
example, an electrolytic capacitor, a film capacitor, or the
like. The capacitor 4a is connected to the output end of
the rectifier unit 3 and has a capacitance to smooth the
10 power rectified by the rectifier unit 3. The waveform of
the power supply voltage output by the commercial power
supply 1 is a full-wave rectified waveform, whereas a voltage
waveform generated in the capacitor 4a by smoothing is a
waveform in which voltage ripple corresponding to the
15 frequency of the commercial power supply 1 is superimposed
on a DC component, and does not greatly pulsate. When the
commercial power supply 1 is a single-phase one, the
frequency of the voltage ripple has, as the main component,
a component twice the frequency of the power supply voltage.
20 When the commercial power supply 1 is a three-phase one, the
frequency of the voltage ripple has, as the main component,
a component six times the frequency of the power supply
voltage. When the power input from the commercial power
supply 1 and the power output from the inverter 5 do not
25 change, the amplitude of the voltage ripple is determined by
the capacitance of the capacitor 4a. For example, the
amplitude of the voltage ripple generated in the capacitor
4a pulsates in such a range that its maximum value is less
than twice its minimum value.
30 [0016] The inverter 5 is connected across the smoothing
unit 4. The inverter 5 includes switching elements and
freewheeling diodes. Specific examples of the switching
elements are semiconductor devices such as insulated-gate
7
bipolar transistors (IGBTs) or metal-oxide semiconductor
field-effect transistors (MOSFETs), and are formed of a
silicon semiconductor. Other than the silicon semiconductor,
a wide bandgap semiconductor may be used. The wide bandgap
5 semiconductor refers to a semiconductor having a bandgap
larger than the bandgap of silicon. A typical wide bandgap
semiconductor is silicon carbide (SiC), gallium nitride
(GaN), gallium oxide (Ga2O3), or diamond. Using a wide
bandgap semiconductor can reduce losses as compared with
10 using a silicon semiconductor. In the inverter 5, the
switching elements are on-off controlled by the control of
the control unit 6. By this control, the power output from
the rectifier unit 3 and the smoothing unit 4 is converted
into the second AC power having an amplitude and phases
15 different from those of the first AC power, according to the
load on the motor 32, and is output to the compressor 30.
[0017] The current detection unit 7 detects a capacitor
input current I1 output from the rectifier unit 3 to the
smoothing unit 4 and the inverter 5, and outputs the detected
20 current value to the control unit 6. The current detection
unit 7 can be used as a detection unit that detects the power
state of the capacitor 4a.
[0018] The current detection unit 8 detects the current
values of two phases of three-phase currents output from the
25 inverter 5, and outputs the detected current values to the
control unit 6. When the detected current values are a Uphase current Iu and a V-phase current Iv, the current value
of a W-phase current Iw that is the remaining one phase can
be obtained by calculation from the relational expression
30 Iu+Iv+Iw=0. Sensors used in the current detection unit 8
may be sensors such as direct current current transducers
(DCCTs), alternating current current transducers (ACCTs), or
shunt resistors, but are not limited to them. Sensors other
8
than these may be used as long as the three-phase current
values can be detected.
[0019] FIG. 2 is a diagram illustrating an exemplary
configuration in which the motor drive device according to
5 the first embodiment is applied to a refrigeration cycle
apparatus. In FIG. 2, a refrigeration cycle apparatus 100
includes the motor drive device 10 according to the first
embodiment. The refrigeration cycle apparatus 100 can be
applied to a product including a refrigeration cycle, such
10 as an air conditioner, a refrigerator, a freezer, or a heat
pump water heater.
[0020] In the refrigeration cycle apparatus 100, the
compressor 30 incorporating the motor 32, a condenser 35, an
expansion valve 36, and an evaporator 37 are installed via
15 refrigerant piping 38. The compressor 30, the condenser 35,
the expansion valve 36, and the evaporator 37 are connected
in a closed loop, forming a refrigerant circuit. Although
not illustrated, installing a four-way valve between the
compressor 30 and the condenser 35 allows the evaporator 37
20 and the condenser 35 to be interchanged between an indoor
unit and an outdoor unit, and allows switching between
heating operation and cooling operation.
[0021] The compressor 30 includes a refrigerant
compression chamber (not illustrated). In the refrigerant
25 compression chamber, a machine for compressing a refrigerant
is provided. An inlet and an outlet (not illustrated) are
connected to the compressor 30, constituting part of the
refrigerant circuit. The motor 32 that drives the compressor
30 includes a stator and a rotor (not illustrated). The
30 stator has a structure in which coils are wound around a
yoke. The rotor is formed of members having the function of
permanent magnets. By the driving of the motor 32, the
machine for compressing the refrigerant is driven, and the
9
refrigerant flowing in from the inlet is compressed in the
compression chamber and flows out from the outlet. FIG. 1
illustrates a case where motor windings in the motor 32 are
Y-connected, but the present invention is not limited to
5 this example. The motor windings in the motor 32 may be Δconnected, or may be designed to be switchable between Y
connection and Δ connection.
[0022] As the compressor 30, a compressor that allows
rotational speed control, that is, an inverter-driven
10 compressor is used in which the rotational speed of the motor
32 is controlled by the inverter 5. Examples of the
inverter-driven compressor include a rotary compressor, a
scroll compressor, and a reciprocating compressor. The drive
characteristics of these compressors are affected by the
15 types of the refrigerant and lubricating oil, the amount of
the lubricating oil, etc. Therefore, depending on conditions,
the torque required to operate the refrigerant compression
chamber increases, so that the output voltage by the control
increases.
20 [0023] FIG. 3 is a diagram for explaining torque in a
rotary compressor and a reciprocating compressor that are
examples of the compressor included in the refrigeration
cycle apparatus illustrated in FIG. 2. In a graph
illustrated in FIG. 3, the vertical axis represents torque,
25 and the horizontal axis represents an angle representing the
rotational position of the rotor. A torque curve C1
represents the relationship between the angle and the load
torque on the rotary compressor, and a torque curve C2
represents the relationship between the angle and the load
30 torque on the reciprocating compressor.
[0024] A comparison between the two torque curves C1 and
C2 shows that compression operation causes torque variation
in both compressors. Further, the comparison shows that an
10
angular range in which the load torque increases is limited
in the reciprocating compressor as compared with in the
rotary compressor.
[0025] Return to the explanation of FIG. 1. The control
5 unit 6 obtains the current value of the input current of the
smoothing unit 4 from the current detection unit 7, and
obtains the current values of the second AC power converted
by the inverter 5 from the current detection unit 8. The
control unit 6 uses the current values detected by the
10 current detection units to control the operation of the
inverter 5, specifically, to perform on-off control on the
switching elements included in the inverter 5.
[0026] In the first embodiment, the control unit 6
controls the inverter 5 such that AC power on sine waves
15 including pulsation corresponding to the pulsation of the
power flowing from the rectifier unit 3 into the capacitor
4a of the smoothing unit 4 is output from the inverter 5 to
the compressor 30. The pulsation corresponding to the
pulsation of the power flowing into the capacitor 4a is, for
20 example, pulsation that varies depending on the frequency or
the like of the pulsation of the power flowing into the
capacitor 4a. Thus, the control unit 6 reduces current
flowing through the capacitor 4a. Note that the control
unit 6 does not need to use all the detected values obtained
25 from the detection units, and may perform control using some
of the detected values.
[0027] The control unit 6 performs control such that one
of the speed, voltage, and current of the motor reaches a
desired state. Here, for the motor 32 used to drive the
30 compressor 30, it is often difficult to attach a position
sensor for detecting the rotor position to the motor 32
because of the structure and the cost. Therefore, the
control unit 6 performs position sensorless control on the
11
motor 32. For a method of the position sensorless control
on the motor 32, there are control methods such as constant
primary flux control and sensorless vector control. In the
first embodiment, as an example, a description is given based
5 on sensorless vector control. A control method described
below can be applied to constant primary flux control with
minor changes.
[0028] In the motor drive device 10, the arrangement of
the components illustrated in FIG. 1 is an example. The
10 arrangement of the components is not limited to the example
illustrated in FIG. 1. For example, the reactor 2 may be
disposed downstream of the rectifier unit 3. The motor drive
device 10 may include a booster unit, or the rectifier unit
3 may have the function of a booster unit.
15 [0029] Next, a characteristic operation in the control
unit 6 in the first embodiment will be described. As
illustrated in FIG. 1, current output from the rectifier
unit 3 to the capacitor 4a and the inverter 5 is represented
by “I1” and is referred to as a “capacitor input current”.
20 Current output from the capacitor 4a and input to the
inverter 5 is represented by “I2” and is referred to as an
“inverter input current”. Current flowing into and out of
the capacitor 4a, that is, current to charge the capacitor
4a or current discharged by the capacitor 4a is represented
25 by “I3” and is referred to as a “charge and discharge
current”.
[0030] The capacitor input current I1 is affected by the
power supply phase of the commercial power supply 1, the
characteristics of elements installed before and after the
30 rectifier unit 3, etc. As a result, the capacitor input
current I1 has characteristics including the power supply
frequency and harmonic components that are frequency
components of the products of the power supply frequency
12
multiplied by integers greater than one. In the capacitor
4a, when the charge and discharge current I3 is large, aging
deterioration of the capacitor 4a is accelerated. In
particular, when an electrolytic capacitor is used as the
5 capacitor 4a, the degree of acceleration of aging
deterioration increases. Therefore, the control unit 6
performs control to bring the charge and discharge current
I3 close to zero by controlling the inverter 5 such that the
capacitor input current I1 and the inverter input current I2
10 become equal, to reduce the charge and discharge current I3.
This can reduce the deterioration of the capacitor 4a.
However, a ripple component caused by the PWM control is
superimposed on the inverter input current I2, and thus the
control unit 6 needs to control the inverter 5 by taking
15 into account the ripple component.
[0031] The control unit 6 monitors the power state of the
capacitor 4a, and provides proper pulsation to the motor 32
to reduce the charge and discharge current I3. Here, the
power state of the capacitor 4a is calculated from the
20 capacitor input current I1, the inverter input current I2,
the charge and discharge current I3, a capacitor voltage
that is the voltage of the capacitor 4a, etc. In the control
unit 6, at least one of these information pieces for
determining the power state of the capacitor 4a is
25 information necessary for the control to reduce the charge
and discharge current I3.
[0032] Using the detected value of the capacitor input
current I1 detected by the current detection unit 7, the
control unit 6 controls the inverter 5 such that a value
30 obtained by removing the PWM ripple from the inverter input
current I2 matches the capacitor input current I1, to add
pulsation to the power output to the motor 32. That is, the
control unit 6 controls the operation of the inverter 5 such
13
that pulsation according to the power state of the capacitor
4a is superimposed on a drive pattern of the motor 32. This
reduces the charge and discharge current I3. In this
description, this control is referred to as “power supply
5 pulsation compensation control”.
[0033] As described above, since the capacitor input
current I1 includes the harmonic components of the power
supply frequency, the inverter input current I2 also includes
the harmonic components of the power supply frequency.
10 Therefore, the motor drive device 10 needs to properly
pulsate the inverter input current I2.
[0034] Furthermore, it is known that even when the
compressor 30 is used, for example, in an air conditioner
and the load on the compressor 30 is substantially constant,
15 that is, the effective value of the inverter input current
I2 is constant, some types of load on the compressor 30
include a mechanism that causes periodic rotational
variation. Therefore, when a compressor load including such
a mechanism is driven, the load torque has periodic variation.
20 Consequently, when constant current load control to drive
the compressor 30 is performed with constant output current
from the inverter 5, that is, constant torque output, speed
variation due to torque difference occurs. There is a
characteristic that the speed variation occurs remarkably in
25 the low speed range, and the speed variation decreases as
the operating point moves to the high speed range. The
amount of the speed variation flows to the outside and thus
is externally observed as vibration. It is required to add
a vibration-control component, for example. Therefore, a
30 measure is often taken to pass pulsating torque, that is, a
pulsating current component through the compressor 30 in
addition to constant current output from the inverter 5,
that is, current for constant torque output, to apply torque
14
responsive to load torque variation from the inverter 5 to
the compressor 30. This can bring the torque difference
close to zero to reduce the speed variation of the motor 32
of the compressor 30 to reduce vibration. As a result, the
5 torque difference between the output torque of the inverter
5 and the load torque can be brought close to zero.
Consequently, the speed variation of the motor 32 included
in the compressor 30 can be reduced, and the vibration of
the compressor 30 can be reduced. In this description, this
10 control is referred to as “load pulsation compensation
control”.
[0035] As described above, there are cases where the motor
drive device 10 must drive the compressor 30 in the high
load range and under the high outside temperature environment.
15 In this case, since the inverter input current I2 inevitably
increases, a problem such as a failure of the capacitor 4a
due to a temperature rise may occur. Further, when the
inverter input current I2 increases, failures or the like of
a circuit component and a soldered portion of the circuit
20 component due to a temperature rise are conceivable.
Furthermore, an increase in motor current flowing through
the motor 32 may cause motor demagnetization, resulting in
performance degradation, a failure, or the like of the motor
32. Therefore, the control unit 6 performs control to
25 temporarily weaken the load pulsation compensation control
and the power supply pulsation compensation control while
performing control to temporarily reduce the rotational
speed on a speed command value. This control can reduce the
inverter input current I2, and thus can reduce heat
30 generation and a temperature rise. In this description, the
operating environment of the motor drive device 10 when
placed in the high load range and under the high outside
temperature environment is referred to as “overload
15
conditions” or “during overload conditions”. Control to
reduce the inverter input current I2 performed when the
operating environment of the motor drive device 10 is the
overload conditions is referred to as “overload compensation
5 control”.
[0036] As described above, in the motor drive device 10
according to the first embodiment, the control unit 6
performs the constant current load control to control the
rotational speed of the motor 32, the load pulsation
10 compensation control to compensate for the load pulsation,
the power supply pulsation compensation control to
compensate for the power supply pulsation, and the overload
compensation control to reduce the inverter input current I2
when the operating environment is the overload conditions.
15 On the other hand, improper allocation by each control may
cause a state in which the rotational speed of the motor 32
cannot follow a speed command, the load pulsation
compensation control results in overcompensation, or power
supply pulsation compensation cannot be satisfactorily
20 controlled, for example. Therefore, in the first embodiment,
the motor drive device 10 is operated such that the operation
of each control becomes proper. Alternatively, the order of
priority among the controls is determined so that the
operation of each control becomes proper. The following
25 describes a specific control method. In this description,
as a coordinate system when the control unit 6 performs
processing, a dq-axis coordinate system that is suitably
used when the motor 32 is a permanent magnet motor is used
for explanation, but the coordinate system is not limited
30 thereto. A control system of the control unit 6 may be
constructed with a γδ-axis coordinate system that is
generally used in position sensorless control.
[0037] First, it is an essential matter in the motor drive
16
device 10 that the motor 32 driven follow a speed command.
Therefore, the control unit 6 performs control that
prioritizes the constant current load control. The control
unit 6 sets a limit value for a q-axis current command that
5 is a torque current command and can be used in each of the
constant current load control, the power supply pulsation
compensation control, and the load pulsation compensation
control. Specifically, the control unit 6 sets limit values
for the power supply pulsation compensation control and the
10 load pulsation compensation control within a range obtained
by subtracting the value of a q-axis current command to be
used in the constant current load control from the total
limit value of q-axis current commands, and generates q-axis
current commands for the power supply pulsation compensation
15 control and the load pulsation compensation control. That
is, the control unit 6 performs the load pulsation
compensation control to compensate for the load pulsation,
and the power supply pulsation compensation control to reduce
the charge and discharge current I3 of the capacitor 4a,
20 while preferentially performing the constant current load
control to control the rotational speed of the motor 32.
[0038] Next, a total q-axis current limit value Iqlim will
be described. The total q-axis current limit value Iqlim
varies depending on the value of a d-axis current Id, the
25 speed of the motor 32, etc. In terms of the demagnetization
limit of the motor 32 in the low speed range, the maximum
current of the inverter 5, etc., the q-axis current limit
value Iqlim is determined, for example, as in formula (1)
below. In this description, the q-axis current limit value
30 Iqlim is sometimes referred to as a “first limit value”.
[0039] Formula 1:
17
[0040] In formula (1), Irmslim represents a phase current
limit value expressed as an effective value, and Id*
represents a d-axis current command that is an exciting
current command. Irmslim is typically set to be lower than a
5 threshold for overcurrent interruption protection in the
inverter 5 by about 10% to 20%. In the high speed range, a
q-axis current Iq that can be passed decreases due to the
effect of voltage saturation. It is well known that when a
q-axis current command becomes excessive, control can become
10 unstable due to a wind-up phenomenon in an integrator. In
formula (1), a decrease in the maximum q-axis current with
an increase in speed is not taken into consideration. Thus,
a numerical formula is derived with a decrease in the maximum
q-axis current taken into account. In the high speed range,
15 the relationship in an approximate expression of formula (2)
is established with respect to Vom where Vom is the limit
value of dq-axis voltage.
[0041] Formula 2:
20 [0042] In formula (2), Vom is the radius of the voltage
limit circle on the dq plane. Formula (2) is organized by
substituting a steady-state voltage equation into
(vd*)2+(vq*)2=Vom
2, ignoring a voltage drop due to armature
resistance. Here, formula (2) is solved for the q-axis
25 current Iq to obtain formula (3).
[0043] Formula 3:
[0044] Thus, when the d-axis current Id is passed to the
limit of the limit value, the q-axis current limit value Iqlim
30 is expressed as in formula (4).
18
[0045] Formula 4:
[0046] When the d-axis current Id is passed until the
voltage is minimized, Φa+LdIdlim=0. At this time, formula (5)
5 holds. In this case, it is found that the q-axis current
limit value Iqlim decreases in inverse proportion to the
electrical angular velocity ωe of the motor 32.
[0047] Formula 5:
10 [0048] As a final conclusion, the q-axis current limit
value Iqlim is set as in formula (6) with both formula (1)
and formula (4) taken into account.
[0049] Formula 6:
15 [0050] In formula (6), MIN is a function to select a
minimum one.
[0051] The configuration of the control unit 6 that
performs the above calculations will be described. FIG. 4
is a block diagram illustrating an exemplary configuration
20 of the control unit included in the motor drive device
according to the first embodiment. The control unit 6
includes a rotor position estimation unit 401, a speed
control unit 402, a flux-weakening control unit 403, a
current control unit 404, coordinate transformation units
25 405 and 406, a PWM signal generation unit 407, subtractors
408 and 412, a load pulsation limit unit 409, a load
pulsation compensation control unit 410, adders 411 and 415,
a power supply pulsation limit unit 413, a power supply
19
pulsation compensation control unit 414, an inverter input
current calculation unit 417, a threshold priority order
control unit 418, and an overload compensation control unit
419. The adders 411 and 415 constitute a q-axis current
5 command generation unit 420.
[0052] For the rotor (not illustrated) included in the
motor 32, the rotor position estimation unit 401 estimates
an estimated phase angle θest that is the direction of the
rotor magnetic poles on the dq axes, and an estimated speed
10 ωest that is the rotor speed, using a dq-axis current vector
Idq and a dq-axis voltage command vector Vdq* for driving the
motor 32.
[0053] The speed control unit 402 automatically adjusts,
that is, generates a q-axis current command Iqsp such that an
15 overload compensation speed command ωlim described later
matches the estimated speed ωest. The q-axis current command
Iqsp is a torque current command for the above-described
constant current load control. In this description, the qaxis current command Iqsp is sometimes referred to as a “first
20 torque current command”.
[0054] The flux-weakening control unit 403 automatically
adjusts a d-axis current command Id* such that the absolute
value of the dq-axis voltage command vector Vdq* falls within
the limit value of a voltage limit value Vlim*. Flux25 weakening control has two broad types: a method of
calculating the d-axis current command Id* from the voltage
limit ellipse equation, and a method of calculating the daxis current command Id* such that a deviation in absolute
value between the voltage limit value Vlim* and the dq-axis
30 voltage command vector Vdq* becomes zero. Either method may
be used.
[0055] The current control unit 404 automatically adjusts
the dq-axis voltage command vector Vdq* such that the dq-axis
20
current vector Idq follows the d-axis current command Id* and
a q-axis current command Iq*. In this description, the qaxis current command Iq* is sometimes referred to as a
“second torque current command”.
5 [0056] The coordinate transformation unit 405 coordinatetransforms the dq-axis voltage command vector Vdq* from dq
coordinates into an AC amount voltage command Vuvw*, according
to the estimated phase angle θest.
[0057] The coordinate transformation unit 406 coordinate10 transforms a motor current Iuvw flowing through the motor 32
from the amount of AC into the dq-axis current vector idq in
dq coordinates, according to the estimated phase angle θest.
As described above, for the motor current Iuvw, the control
unit 6 can obtain, of the current values of the three phases
15 output from the inverter 5, the current values of the two
phases detected by the current detection unit 8, and the
current value of the remaining one phase by calculation using
the current values of the two phases.
[0058] The PWM signal generation unit 407 generates a PWM
20 signal based on the voltage command Vuvw* coordinatetransformed by the coordinate transformation unit 405. The
control unit 6 outputs the PWM signal generated by the PWM
signal generation unit 407 to the switching elements of the
inverter 5 to apply voltage to the motor 32.
25 [0059] The subtractor 408 generates a first q-axis
current margin Iqmargin that is the difference between the qaxis current limit value Iqlim and the absolute value of the
q-axis current command Iqsp described above. When the value
of the q-axis current command Iqsp is positive, calculation
30 of the absolute value is unnecessary. The q-axis current
limit value Iqlim is a limit value for the q-axis current
command Iq* to be input to the current control unit 404. The
first q-axis current margin Iqmargin is the remainder when the
21
amount of current of the q-axis current command Iqsp required
for the constant current load control is subtracted from the
q-axis current limit value Iqlim, and is a value allocatable
to the load pulsation compensation control, the power supply
5 pulsation compensation control, and the overload
compensation control. Note that Iqlim-|Iqsp| is affected by
speed pulsation, bus voltage pulsation, etc., and thus the
subtractor 408 may perform smoothing using a low-pass filter
as in formula (7). In this description, the first q-axis
10 current margin Iqmargin, which is the difference between the
q-axis current limit value Iqlim and the q-axis current
command Iqsp, is sometimes referred to as a “first difference”.
[0060] Formula 7:
15 [0061] In formula (7), T is the filter time constant and
represents the reciprocal of the cutoff angular frequency,
and s represents the Laplace transform variable. Next, the
control unit 6 allocates the first q-axis current margin
Iqmargin to the load pulsation compensation control and the
20 power supply pulsation compensation control.
[0062] The threshold priority order control unit 418
transmits a preset threshold I2lim* to the load pulsation
limit unit 409, the power supply pulsation limit unit 413,
and the overload compensation control unit 419 according to
25 a predetermined priority order. The threshold I2lim* is
transmitted to at least one of the load pulsation limit unit
409, the power supply pulsation limit unit 413, and the
overload compensation control unit 419 individually,
sequentially, or simultaneously, according to the priority
30 order.
[0063] In the load pulsation limit unit 409, an input
signal is multiplied by a load pulsation compensation limit
22
ratio KlimAVS for limiting the load pulsation compensation
control. In the power supply pulsation limit unit 413, an
input signal is multiplied by a power supply pulsation
compensation limit ratio KlimD2V for limiting the power supply
5 pulsation compensation control. In the overload
compensation control unit 419, an input signal is multiplied
by an overload compensation limit ratio KlimOL for limiting
the overload compensation control.
[0064] In a specific example of priority control where
10 the inverter input current I2 is reduced only, for example,
by the load pulsation compensation control, the power supply
pulsation compensation control and the overload compensation
control are not limited, and thus the limit ratios for these
controls do not decrease. In this example, the load
15 pulsation compensation control is performed until the
inverter input current I2 falls below the threshold I2lim*.
When the inverter input current I2 falls below the threshold
I2lim*, the limit ratios are restored. In a case where limits
are performed in the priority order, when the inverter input
20 current I2 falls below the threshold I2lim*, the limit ratios
are restored in the reverse order of the priority order. In
a case where priorities are not assigned, limits are
simultaneously imposed. When the inverter input current I2
falls below the threshold I2lim*, the limit ratios are
25 simultaneously restored. The following describes individual
operations in the control units.
[0065] First, the inverter input current calculation unit
417 obtains the dq-axis current vector Idq from the
coordinate transformation unit 406, and calculates the
30 inverter input current I2 using the d-axis current Id and
the q-axis current Iq as shown in formula (8).
23
[0066] Formula 8:
[0067] The load pulsation limit unit 409 obtains the first
q-axis current margin Iqmargin from the subtractor 408, obtains
5 the inverter input current I2 from the inverter input current
calculation unit 417, and obtains the threshold I2lim* from
the threshold priority order control unit 418. The load
pulsation limit unit 409 determines the load pulsation
compensation limit ratio KlimAVS in the load pulsation
10 compensation control by comparing the inverter input current
I2 with the threshold I2lim*. As shown in formula (9), the
load pulsation limit unit 409 multiplies the first q-axis
current margin Iqmargin obtained from the subtractor 408 by
the load pulsation compensation limit ratio KlimAVS to generate
15 a current limit value IqlimAVS for the load pulsation
compensation control. In this description, the load
pulsation compensation limit ratio KlimAVS is sometimes
referred to as a “first limit ratio”, and the load pulsation
limit unit 409 is sometimes referred to as a “first limit
20 ratio multiplier”.
[0068] Formula 9:
[0069] The load pulsation compensation limit ratio KlimAVS
is a limit ratio for the first q-axis current margin Iqmargin,
25 and is a variable greater than or equal to zero and less
than or equal to one. The load pulsation compensation limit
ratio KlimAVS may be set according to the power state of the
capacitor 4a, the operating state of the motor 32, the
operating state of an air conditioner when the motor drive
30 device 10 is used as a refrigeration cycle apparatus in the
air conditioner, etc. Thus, the current limit value IqlimAVS
for the load pulsation compensation control is set using the
24
first q-axis current margin Iqmargin. In this description,
the current limit value IqlimAVS for the load pulsation
compensation control is sometimes referred to as a “second
limit value”.
5 [0070] Here, a method by which the load pulsation limit
unit 409 determines the load pulsation compensation limit
ratio KlimAVS will be supplemented. As described above, the
q-axis current Iq that can be used in the power supply
pulsation compensation control and the load pulsation
10 compensation control is limited. Therefore, the load
pulsation limit unit 409 determines the load pulsation
compensation limit ratio KlimAVS to determine the priority
order of the load pulsation compensation control and the
power supply pulsation compensation control with respect to
15 each compensation control. In the first embodiment, to
determine the limit ratio of the q-axis current Iq, the load
pulsation limit unit 409 determines the load pulsation
compensation limit ratio KlimAVS, based on the inverter input
current I2, the priority order of the load pulsation
20 compensation control, the power supply pulsation
compensation control, and the overload compensation control,
and the threshold I2lim*.
[0071] The load pulsation compensation control unit 410
generates a load pulsation compensation q-axis current
25 command IqAVS, using the current limit value IqlimAVS for the
load pulsation compensation control. The load pulsation
compensation q-axis current command IqAVS is a torque current
command for the load pulsation compensation control.
Specifically, the load pulsation compensation control unit
30 410 performs the load pulsation compensation control within
the current limit value IqlimAVS for the load pulsation
compensation control generated by the load pulsation limit
unit 409, and generates the load pulsation compensation q-
25
axis current command IqAVS. The load pulsation compensation
q-axis current command IqAVS is expressed as in formula (10).
The magnitude relationships among the first q-axis current
margin Iqmargin, the current limit value IqlimAVS for the load
5 pulsation compensation control, and the load pulsation
compensation q-axis current command IqAVS are
Iqmargin≥IqlimAVS≥IqAVS. In this description, the load pulsation
compensation q-axis current command IqAVS is sometimes
referred to as a “first compensation value”.
10 [0072] Formula 10:
[0073] In the control of the first embodiment, there may
be cases where the load pulsation compensation control unit
410 does not use up the current limit value IqlimAVS for the
15 load pulsation compensation control. Therefore, as shown in
formula (11), the subtractor 412 generates a second q-axis
current margin IqmarginD2V that is the difference between the
first q-axis current margin Iqmargin and the load pulsation
compensation q-axis current command IqAVS. In this
20 description, the second q-axis current margin IqmarginD2V is
sometimes referred to as a “second difference”.
[0074] Formula 11:
[0075] The power supply pulsation limit unit 413 obtains
25 the second q-axis current margin IqmarginD2V from the subtractor
412, obtains the inverter input current I2 from the inverter
input current calculation unit 417, and obtains the threshold
I2lim* from the threshold priority order control unit 418.
The power supply pulsation limit unit 413 determines the
30 power supply pulsation compensation limit ratio KlimD2V in the
power supply pulsation compensation control by comparing the
inverter input current I2 with the threshold I2lim*. As shown
26
in formula (12), the power supply pulsation limit unit 413
multiplies the second q-axis current margin IqmarginD2V obtained
from the subtractor 412 by the power supply pulsation
compensation limit ratio KlimD2V to generate a current limit
5 value IqlimD2V for the power supply pulsation compensation
control. In this description, the power supply pulsation
compensation limit ratio KlimD2V is sometimes referred to as
a “second limit ratio”, and the power supply pulsation limit
unit 413 is sometimes referred to as a “second limit ratio
10 multiplier”.
[0076] Formula 12:
[0077] The power supply pulsation compensation limit
ratio KlimD2V is a limit ratio for the second q-axis current
15 margin IqmarginD2V, and is a variable greater than or equal to
zero and less than or equal to one. The power supply
pulsation compensation limit ratio KlimD2V may be set according
to the power state of the capacitor 4a, the operating state
of the motor 32, the operating state of an air conditioner
20 when the motor drive device 10 is used as a refrigeration
cycle apparatus in the air conditioner, etc. Thus, the
current limit value IqlimD2V for the power supply pulsation
compensation control is set using the second q-axis current
margin IqmarginD2V. In this description, the current limit
25 value IqlimD2V for the power supply pulsation compensation
control is sometimes referred to as a “third limit value”.
[0078] The power supply pulsation compensation control
unit 414 generates a current amplitude IqD2V for the power
supply pulsation compensation control, using the current
30 limit value IqlimD2V for the power supply pulsation
compensation control. The current amplitude IqD2V for the
power supply pulsation compensation control is a torque
current command for the power supply pulsation compensation
27
control. Specifically, the power supply pulsation
compensation control unit 414 determines the current
amplitude IqD2V for the power supply pulsation compensation
control as in formula (13). When the absolute value of the
5 q-axis current command Iqsp is greater than or equal to the
current limit value IqlimD2V for the power supply pulsation
compensation control, the power supply pulsation
compensation control unit 414 selects the current limit value
IqlimD2V for the power supply pulsation compensation control
10 as the current amplitude IqD2V for the power supply pulsation
compensation control. When the absolute value of the q-axis
current command Iqsp is less than the current limit value
IqlimD2V for the power supply pulsation compensation control,
the power supply pulsation compensation control unit 414
15 selects the absolute value of the q-axis current command Iqsp
as the current amplitude IqD2V for the power supply pulsation
compensation control. In this description, the current
amplitude IqD2V is sometimes referred to as a “second
compensation value”.
20 [0079] Formula 13:
[0080] In the processing of formula (13) above, when the
absolute value of the q-axis current command Iqsp is equal to
the current limit value IqlimD2V for the power supply pulsation
25 compensation control, the current limit value IqlimD2V for the
power supply pulsation compensation control is selected, but
the present invention is not limited thereto. When the
absolute value of the q-axis current command Iqsp is equal to
the current limit value IqlimD2V for the power supply pulsation
30 compensation control, the absolute value of the q-axis
28
current command Iqsp may be selected.
[0081] The q-axis current command generation unit 420
generates the q-axis current command Iq* using the q-axis
current command Iqsp, the load pulsation compensation q-axis
5 current command IqAVS, and the current amplitude IqD2V for the
power supply pulsation compensation control. Specifically,
in the q-axis current command generation unit 420, the adder
411 adds the q-axis current command Iqsp and the load
pulsation compensation q-axis current command IqAVS. The
10 adder 415 adds the result of the addition by the adder 411,
which is the q-axis current command Iqsp+the load pulsation
compensation q-axis current command IqAVS, and the current
amplitude IqD2V for the power supply pulsation compensation
control. The q-axis current command generation unit 420
15 outputs the result of the addition by the adder 415 as the
q-axis current command Iq* to the current control unit 404.
[0082] The overload compensation control unit 419 obtains
a speed command ω*, obtains the inverter input current I2
from the inverter input current calculation unit 417, and
20 obtains the threshold I2lim* from the threshold priority order
control unit 418. The overload compensation control unit
419 determines the overload compensation limit ratio KlimOL
in the overload compensation control by comparing the
inverter input current I2 with the threshold I2lim*. As shown
25 in formula (14), the overload compensation control unit 419
multiplies the speed command ω* by the overload compensation
limit ratio KlimOL to generate the overload compensation speed
command ωlim. In this description, the overload compensation
limit ratio KlimOL is sometimes referred to as a “third limit
30 ratio”, and the overload compensation control unit 419 is
sometimes referred to as a “third limit ratio multiplier”.
29
[0083] Formula 14:
[0084] When the motor drive device 10 is used as a
refrigeration cycle apparatus in an air conditioner or the
5 like, the speed command ω* is based, for example, on a
temperature detected by a temperature sensor (not
illustrated), information indicating a set temperature
specified from a remote controller that is an operating unit
(not illustrated), operation mode selection information,
10 instruction information on an operation start and an
operation end, etc. Examples of operation modes include
heating, cooling, and dehumidification.
[0085] By the multiplication of the speed command ω* by
the overload compensation limit ratio KlimOL, the rotational
15 speed can be temporarily limited. Acceleration and
deceleration control for limiting the rotational speed is
performed according to the acceleration and deceleration
rate of the motor 32. In this description, the overload
compensation speed command ωlim is sometimes referred to as
20 a “third compensation value”.
[0086] As described above, the speed control unit 402
automatically adjusts the q-axis current command Iqsp such
that the overload compensation speed command ωlim matches the
estimated speed ωest. That is, the q-axis current command
25 Iqsp, which is the first torque current command, is
compensated for by the overload compensation speed command
ωlim, which is the third compensation value.
[0087] Next, the threshold I2lim* will be described. As
described above, the threshold I2lim* is a control parameter
30 used in control to limit the inverter input current I2. The
threshold I2lim* varies depending on the rotational speed of
the motor 32, the ambient temperature of the motor drive
device 10, etc. In this description, the threshold I2lim* is
30
sometimes referred to as a “fourth limit value”.
[0088] With respect to the q-axis current limit value
Iqlim, the threshold I2lim* is affected by various factors such
as the heat dissipation structure and circuit configuration
5 of the inverter 5, the capacitor capacitance, and the
operating environment, and thus is set to a value obtained
by determining a value by performing a test and providing a
margin of about 10% to the value determined by the test.
[0089] As described above, the range of values that can
10 be taken on by the load pulsation compensation limit ratio
KlimAVS, the power supply pulsation compensation limit ratio
KlimD2V, and the overload compensation limit ratio KlimOL, which
are set based on the threshold I2lim*, is greater than or
equal to zero and less than or equal to one for all the three
15 limit ratios. When the inverter input current I2 is higher
than or equal to the threshold I2lim* or exceeds the threshold
I2lim*, the value of each limit ratio is gradually decreased
from one. The priority order in which the three limit ratios
are decreased is affected by various factors such as the
20 heat dissipation structure and circuit configuration of the
inverter 5, the capacitor capacitance, and the operating
environment, and is also affected by performance required of
the inverter 5, the demagnetization limit of the motor 32 in
the high speed range, etc. Therefore, it is also desirable
25 to determine the priority order by performing a test.
Further, it is also desirable to determine a lower limit of
how much to decrease by performing a test. As for how to
decrease the limit ratios when the threshold I2lim* is
exceeded, the limit ratios can be basically decreased
30 linearly in accordance with increases in the inverter input
current I2. However, there is no problem in making the
amount of decrease nonlinear by using a high-order function,
for example.
31
[0090] As described above, the control unit 6 changes the
load pulsation compensation limit ratio KlimAVS, the power
supply pulsation compensation limit ratio KlimD2V, and the
overload compensation limit ratio KlimOL according to the
5 circumstances, to appropriately set those values. This makes
it possible to properly perform the power supply pulsation
compensation control, the load pulsation compensation
control, and the overload compensation control while
following the speed command ω*.
10 [0091] Next, the operations of the units in the control
unit 6 described above will be described in an operating
mode as viewed from the entire control unit 6. FIG. 5 is a
flowchart for explaining the operations of principal
components in the control unit included in the motor drive
15 device according to the first embodiment.
[0092] The control unit 6 calculates the inverter input
current I2 from the dq-axis current vector Idq (step S1).
[0093] The control unit 6 sends the threshold I2lim* to
limit units that perform the power supply pulsation
20 compensation control, the load pulsation compensation
control, and the overload compensation control, according to
a predetermined priority order (step S2). The limit units
referred to here are the load pulsation limit unit 409, the
power supply pulsation limit unit 413, and the overload
25 compensation control unit 419 described above.
[0094] The control unit 6 determines the load pulsation
compensation limit ratio KlimAVS, the power supply pulsation
compensation limit ratio KlimD2V, and the overload
compensation limit ratio KlimOL by comparing the inverter
30 input current I2 with the threshold I2lim* (step S3).
[0095] The control unit 6 multiplies the speed command ω*
by the overload compensation limit ratio KlimOL to generate
the overload compensation speed command ωlim (step S4). The
32
overload compensation speed command ωlim is generated as the
limit value of the speed command ω*.
[0096] The control unit 6 generates the first q-axis
current margin Iqmargin, which is the difference between the
5 q-axis current limit value Iqlim and the absolute value of
the q-axis current command Iqsp, and generates the current
limit value IqlimAVS for the load pulsation compensation
control (step S5). As described above, the current limit
value IqlimAVS for the load pulsation compensation control is
10 generated by multiplying the first q-axis current margin
Iqmargin by the load pulsation compensation limit ratio KlimAVS.
[0097] The control unit 6 performs the load pulsation
compensation control within the current limit value IqlimAVS
and generates the load pulsation compensation q-axis current
15 command IqAVS (step S6).
[0098] The control unit 6 generates the second q-axis
current margin IqmarginD2V, which is the difference between the
first q-axis current margin Iqmargin and the load pulsation
compensation q-axis current command IqAVS (step S7). As
20 described above, the second q-axis current margin IqmarginD2V
is a q-axis current margin for the power supply pulsation
compensation control.
[0099] The control unit 6 multiplies the second q-axis
current margin IqmarginD2V by the power supply pulsation
25 compensation limit ratio KlimD2V to generate the current limit
value IqlimD2V for the power supply pulsation compensation
control (step S8).
[0100] The control unit 6 performs the power supply
pulsation compensation control within the current limit
30 value IqlimD2V and generates the current amplitude IqD2V for the
power supply pulsation compensation control (step S9).
[0101] The control unit 6 adds the q-axis current command
Iqsp, the load pulsation compensation q-axis current command
33
IqAVS, and the current amplitude IqD2V for the power supply
pulsation compensation control to generate the q-axis
current command Iq* (step S10).
[0102] Next, a hardware configuration of the control unit
5 6 will be described. FIG. 6 is a diagram illustrating an
example of a hardware configuration that implements the
control unit included in the motor drive device according to
the first embodiment.
[0103] The control unit 6 is implemented by a processor
10 61 and a memory 62. The processor 61 is a central processing
unit (CPU), a central processor, a processing device, an
arithmetic device, a microcomputer, a microprocessor, a
digital signal processor (DSP), or a system large-scale
integration (LSI). The memory 62 can be exemplified by
15 nonvolatile or volatile semiconductor memory such as readonly memory (ROM), random-access memory (RAM), flash memory,
an erasable programmable read-only memory (EPROM), or an
electrically erasable programmable read-only memory (EEPROM)
(registered trademark). The memory 62 is not limited to
20 these and may be a magnetic disk, an optical disk, a compact
disc, a mini disc, or a digital versatile disc (DVD).
[0104] As described above, the motor drive device
according to the first embodiment includes the rectifier
unit, the capacitor connected to the output end of the
25 rectifier unit, the inverter connected across the capacitor,
and the control unit. The rectifier unit rectifies the first
AC power supplied from the commercial power supply. The
inverter generates the second AC power and outputs the second
AC power to the motor. The control unit controls the
30 operation of the inverter such that pulsation according to
the power state of the capacitor is superimposed on the drive
pattern of the motor, to reduce the charge and discharge
current of the capacitor. The control unit performs the
34
load pulsation compensation control to compensate for the
load pulsation, the power supply pulsation compensation
control to reduce the charge and discharge current of the
capacitor, and the overload compensation control to reduce
5 the inverter input current input to the inverter, while
preferentially performing the constant current load control
to control the rotational speed of the motor. This can
prevent a decrease in the reliability of the unit even in
driving in the high load range and under the high outside
10 temperature environment. Furthermore, since the motor
current can be reduced by reducing the inverter input current,
it is possible to prevent performance degradation and
failures due to the demagnetization of the motor.
[0105] In the motor drive device according to the first
15 embodiment, the control unit can be configured with the speed
control unit, the load pulsation compensation control unit,
the power supply pulsation compensation control unit, and
the overload compensation control unit. The speed control
unit generates the first torque current command that is a
20 command for the constant current load control in a rotating
coordinate system. The load pulsation compensation control
unit generates the first compensation value for the load
pulsation compensation control, using the second limit value
set using the first difference between the first limit value
25 for the first torque current command and the first torque
current command. The power supply pulsation compensation
control unit generates the second compensation value for the
power supply pulsation compensation control, using the third
limit value set using the second difference between the first
30 difference and the first compensation value. The overload
compensation control unit generates the third compensation
value for the overload compensation control, using the fourth
limit value.
35
[0106] In the configuration of the control unit, the
second limit value is generated by multiplying the first
difference by the first limit ratio greater than or equal to
zero and less than or equal to one. The third limit value
5 is generated by multiplying the second difference by the
second limit ratio greater than or equal to zero and less
than or equal to one. The third compensation value is
generated by multiplying the rotational speed command by the
third limit ratio greater than or equal to zero and less
10 than or equal to one. Thus, the first torque current command
that is the basis of the voltage command vector for driving
the motor is compensated for by the third compensation value.
[0107] In the motor drive device according to the first
embodiment, the first torque current command is limited by
15 at least one of the first to third limit ratios, and the
first to third limit ratios are assigned priorities for use.
Alternatively, the first torque current command is limited
by at least one of the first to third limit ratios, and the
first to third limit ratios have a lower limit set for use.
20 Then, the first to third limit ratios can be changed based
on the inverter input current. This makes it possible to
properly perform the power supply pulsation compensation
control, the load pulsation compensation control, and the
overload compensation control while following the speed
25 command. As a result, an event such as an inability to
follow the speed command, excessive compensation of the load
pulsation compensation, or unsatisfactory control of the
power supply pulsation compensation can be prevented from
occurring.
30 [0108] Second Embodiment.
In the first embodiment, the load pulsation
compensation limit ratio KlimAVS, the power supply pulsation
compensation limit ratio KlimD2V, and the overload
36
compensation limit ratio KlimOL are determined based on the
inverter input current I2. In the second embodiment, these
three limit ratios are determined based on temperature
information. The configuration of a motor drive device
5 according to the second embodiment is the same as the
configuration of the motor drive device 10 according to the
first embodiment. The flow of processing by a control unit
according to the second embodiment is also the same as the
flow of the processing illustrated in the flowchart of FIG.
10 5. In the second embodiment, only differences from the first
embodiment will be described, and duplicate content will not
be described.
[0109] In the second embodiment, in the motor drive device
10, the load pulsation compensation limit ratio KlimAVS, the
15 power supply pulsation compensation limit ratio KlimD2V, and
the overload compensation limit ratio KlimOL are determined,
based on temperature information on a part where the rise of
temperature is severe, instead of the inverter input current
I2. An example of the part where the rise of temperature is
20 severe is the inverter 5 or the capacitor 4a.
[0110] The temperature information may be obtained by a
method of direct detection using a temperature sensor such
as a thermocouple, or by an indirect method without using a
temperature sensor. One example is a method of estimating
25 the temperature of an area of interest from a loss due to
current flowing into the area of interest.
[0111] As described above, according to the motor drive
device of the second embodiment, in the configuration and
control of the motor drive device of the first embodiment,
30 the first to third limit ratios can be changed based on the
temperature information on the inverter 5 or the capacitor
4a. This makes it possible to properly perform the power
supply pulsation compensation control, the load pulsation
37
compensation control, and the overload compensation control
while following the speed command. As a result, the same
effects as in the first embodiment are achieved, that is, an
event such as an inability to follow the speed command,
5 excessive compensation of the load pulsation compensation,
or unsatisfactory control of the power supply pulsation
compensation can be prevented from occurring.
[0112] The configurations described in the above
embodiments illustrate an example, and can be combined with
10 another known art. The embodiments can be combined with
each other. The configurations can be partly omitted or
changed without departing from the gist.
Reference Signs List
15 [0113] 1 commercial power supply; 2 reactor; 3
rectifier unit; 4 smoothing unit; 4a capacitor; 5
inverter; 6 control unit; 7, 8 current detection unit; 10
motor drive device; 30 compressor; 32 motor; 35 condenser;
36 expansion valve; 37 evaporator; 38 refrigerant piping;
20 61 processor; 62 memory; 100 refrigeration cycle
apparatus; 401 rotor position estimation unit; 402 speed
control unit; 403 flux-weakening control unit; 404 current
control unit; 405, 406 coordinate transformation unit; 407
PWM signal generation unit; 408, 412 subtractor; 409 load
25 pulsation limit unit; 410 load pulsation compensation
control unit; 411, 415 adder; 413 power supply pulsation
limit unit; 414 power supply pulsation compensation control
unit; 417 inverter input current calculation unit; 418
threshold priority order control unit; 419 overload
30 compensation control unit; 420 q-axis current command
generation unit.

WE CLAIM:
[Claim 1] A motor drive device comprising:
a rectifier unit to rectify first AC power supplied
from a commercial power supply;
5 a capacitor connected to an output end of the rectifier
unit;
an inverter connected across the capacitor, to generate
second AC power and output the second AC power to a motor;
and
10 a control unit to control operation of the inverter
such that pulsation according to a power state of the
capacitor is superimposed on a drive pattern of the motor,
to reduce a charge and discharge current of the capacitor,
wherein
15 the control unit performs load pulsation compensation
control to compensate for load pulsation, power supply
pulsation compensation control to reduce the charge and
discharge current of the capacitor, and overload
compensation control to reduce an inverter input current
20 input to the inverter, while preferentially performing
constant current load control to control a rotational speed
of the motor.
[Claim 2] The motor drive device according to claim 1,
25 wherein
the control unit includes
a speed control unit to generate a first torque current
command that is a command for the constant current load
control in a rotating coordinate system,
30 a load pulsation compensation control unit to generate
a first compensation value for the load pulsation
compensation control, using a second limit value set using
a first difference between a first limit value for the first
39
torque current command and the first torque current command,
a power supply pulsation compensation control unit to
generate a second compensation value for the power supply
pulsation compensation control, using a third limit value
5 set using a second difference between the first difference
and the first compensation value, and
an overload compensation control unit to generate a
third compensation value for the overload compensation
control, using a fourth limit value.
10
[Claim 3] The motor drive device according to claim 2,
wherein
the second limit value is generated by multiplying the
first difference by a first limit ratio greater than or equal
15 to zero and less than or equal to one,
the third limit value is generated by multiplying the
second difference by a second limit ratio greater than or
equal to zero and less than or equal to one,
the third compensation value is generated by
20 multiplying a rotational speed command by a third limit ratio
greater than or equal to zero and less than or equal to one,
and
the first torque current command is compensated for by
the third compensation value.
25
[Claim 4] The motor drive device according to claim 3,
wherein
the first torque current command is limited by at least
one of the first to third limit ratios, and the first to
30 third limit ratios are assigned priorities for use.
[Claim 5] The motor drive device according to claim 3,
wherein
40
the first torque current command is limited by at least
one of the first to third limit ratios, and the first to
third limit ratios have a lower limit set for use.
5 [Claim 6] The motor drive device according to any one of
claims 3 to 5, wherein
the first to third limit ratios can be changed based on
the inverter input current.
10 [Claim 7] The motor drive device according to claim 3,
wherein
the first to third limit ratios can be changed based on
temperature information on the inverter or the capacitor.
15 [Claim 8] A refrigeration cycle apparatus, comprising the
motor drive device according to any one of claims 1 to 7.