JP2005168196A - Inverter controller, drive controller of compressor, refrigerator and inverter control method, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter controller capable of starting to control an inverter of such type as the rotational position of a rotor is estimated on the basis of a current flowing a motor, even if a start load is relatively high. <P>SOLUTION: The inverter controller detects the current flowing a motor, and estimates a rotational position θm of a rotor by calculating the current value at a position estimating part. On the basis of the estimated rotational position, it generates and outputs a polyphase PMW signal which makes an inverter main circuit output a pseudo sine wave voltage signal. A PMW signal generating means sets a carrier wave frequency to be relatively high during a start control period where estimating of position by the position estimating part is unstable from the starting up time of the motor (steps S1-S7), while sets the carrier wave frequency to be relatively low when reaching a normal control state where estimating of position by the position estimating part becomes stable to allow succession (step S8). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention estimates the rotational position of the rotor by detecting and calculating the current flowing through the motor, and outputs a pseudo sine wave voltage signal to the inverter main circuit based on the estimated rotational position. An inverter control device that generates and outputs a signal, an inverter control method, a drive control device for a compressor that includes the inverter control device, a refrigerator that includes the drive control device for the compressor, and a computer program that controls the inverter The present invention relates to a stored storage medium.

For example, in order to make the cooling capacity of a refrigeration cycle incorporated in a refrigerator, an air conditioner, etc. variable, a compressor motor constituting the refrigeration cycle is driven by an inverter control device that is switching-controlled by a PWM signal. Yes. Patent Document 1 discloses a so-called sensorless vector control configuration in which the inverter control device performs vector control without using a position sensor in order to cancel torque fluctuations that occur as the compressor load changes. Has been.
JP2001-183017

  In sensorless vector control, instead of using a position sensor, the motor phase current is detected by a shunt resistor, etc., placed in the inverter main circuit, and the detected current value is calculated using the electrical equivalent equation of the motor. The position is estimated. However, in the sensorless vector control, when the rotation of the motor is in a low speed region and the detected current value is low, the control accuracy decreases. Therefore, when starting a motor, generally it is started by forced commutation, and switching to vector control is performed when the number of revolutions increases to some extent.

  Also, in a refrigeration cycle incorporating a reciprocating compressor, when the cycle is temporarily stopped after a certain amount of cooling, the compressor refrigerant suction pressure is low and the discharge pressure is high, that is, (discharge pressure) )-(Suction pressure) differential pressure is large. If you try to restart the compressor from that state, the start load of the motor is difficult and difficult, so it is necessary to wait for the start for a certain period of time and start the restart when the differential pressure decreases. Yes. And, delaying the restart and waiting means reducing the temperature difference between the discharge side and the suction side, so the cooling that has been advanced up to that point is wasted during that time, and was wasted again during the restart The minutes will be cooled again. Therefore, there is a problem that energy required for cooling is wasted in addition to delaying restart of cooling.

  The present invention has been made in view of the above circumstances, and its purpose is to control an inverter that estimates the rotational position of the rotor based on the current flowing through the motor, even when the starting load is relatively large. , Inverter control device capable of starting, inverter control method, compressor drive control device including the inverter control device, refrigerator including the compressor drive control device, and computer for controlling the inverter It is to provide a storage medium in which a program is stored.

In order to achieve the above object, an inverter control device according to claim 1 comprises:
Current detection means for detecting the current flowing through the motor;
Position estimating means for estimating the rotational position of the rotor by calculating the current value;
PMW signal generating means for generating and outputting a multiphase PMW signal for outputting a pseudo sine wave voltage signal to an inverter main circuit for driving the motor based on the estimated rotational position,
The PMW signal generation means includes:
The PMW signal generation means sets the carrier frequency of the PWM signal in the start control period until a predetermined time has elapsed from the start of the motor start to be higher than the carrier frequency in the steady control state after the period has elapsed. It is configured.

  In general, the carrier frequency of the PWM signal output to the inverter main circuit for rotationally driving the motor is determined by a trade-off between the required control accuracy and the switching loss generated in the inverter main circuit. That is, if the carrier frequency is set high, the waveform of the pseudo sine wave voltage signal can be approximated to a sine wave, and the control accuracy is improved, while the switching loss increases. In the conventional control method, PWM control is performed at a constant carrier frequency determined in consideration of the trade-off.

  However, the inventors of the present invention have experimentally confirmed that a larger output torque can be obtained when the carrier frequency of the PWM signal is set relatively high in the low-speed rotation region of the motor. Therefore, by setting the carrier frequency in the start control period from the start of the motor to the steady control state to be higher than the subsequent steady control state, the motor can be easily operated even when the start load is high. It became possible to start. Since the carrier frequency is lowered in the steady control state, an increase in switching loss is suppressed as much as possible.

  According to a fifth aspect of the present invention, there is provided a compressor drive control device comprising the inverter control device according to any one of the first to fourth aspects, wherein the reciprocating compressor is driven by a motor. That is, if the present invention is applied to a case where there is a case where the compressor motor restarts from a state where the difference between the discharge pressure and the suction pressure is large, such as a reciprocating compressor, it is extremely effective.

  A refrigerator according to claim 6 is characterized in that a refrigerating cycle is constituted by a reciprocating compressor, and the compressor drive control device according to claim 5 is provided. If comprised in this way, even when it is necessary to interrupt a refrigerating cycle in the cooling control of a refrigerator, the refrigerating cycle can be restarted in a short time. Further, energy required for cooling at the time of restarting is not wasted as much as possible, so that energy saving can be further promoted.

  According to the present invention, when the rotational position of the rotor is estimated and the motor is driven by PWM control, the output torque of the motor in the low speed rotation region can be obtained more greatly. When applied to a compressor drive control device, the motor can be easily started even when the starting load is high due to the differential pressure of the compressor. Furthermore, energy saving can be achieved by applying to a refrigerator.

  Hereinafter, an embodiment of the present invention applied to a compressor drive control device constituting a refrigeration cycle incorporated in a refrigerator will be described with reference to the drawings. FIG. 6 is a configuration diagram of the refrigeration cycle 50 of the present embodiment. As shown in this figure, a condenser 52, a decompressor 53, and an evaporator 54 are connected downstream of a reciprocating compressor (reciprocating compressor) 51 capable of changing the capacity, and the refrigerant circulates in the compressor 51. It has a structure to do.

  FIG. 4 is an electrical configuration diagram illustrating the inverter device. In FIG. 2, an inverter device (drive control device) 1 includes a target torque calculation unit 2, a target current calculation unit 3, a target voltage calculation unit 4, a dq / αβ conversion unit 5, a PWM signal generation unit 6, and an inverter main circuit 7. The motor current detection unit 8 (corresponding to current detection means), the three-phase / two-phase conversion unit 9, the αβ / dq conversion unit 10 and the position estimation unit 11 (corresponding to position estimation means) are configured. The rotational position detection device includes a motor current detection unit 8, a three-phase / two-phase conversion unit 9, an αβ / dq conversion unit 10, and a position estimation unit 11.

  The inverter main circuit 7 is configured as a voltage type inverter formed by connecting switching elements such as IGBTs as a three-phase bridge, and the motor current detection unit 8 includes motor currents Ia, Ib, Ic of a phase, b phase, and c phase. It is composed of a hole CT for detecting (hereinafter simply referred to as current). Other components are processed by software by a control means including a processor such as a DSP. The PWM signal generator 6 generates a three-phase PWM signal whose pulse width changes so that a pseudo sine wave voltage signal is output to the inverter main circuit 7. Includes a three-phase converter.

  The motor 12 driven by the inverter device 1 drives the compressor 21 and is a salient pole motor having a 4-pole permanent magnet on the rotor. The motor 12 is incorporated in the compressor 21 and is placed in an environment where it is exposed to a high-temperature refrigerant. For this reason, a hall sensor (position detector) for detecting the position of the rotor cannot be installed, and the inverter device 1 performs so-called sensorless driving.

  Since the inverter device 1 performs so-called vector control that independently controls the current in the field direction (d-axis) and the current in the direction orthogonal to it (q-axis), the speed control that controls the rotational speed of the motor 12. A loop and a current control loop for controlling the current of the motor 12 are configured. Note that details of basic operations related to vector control of the inverter device 1 are the same as those disclosed in JP-A-2003-209989.

Further, in the configuration disclosed in Japanese Patent Application Laid-Open No. 2003-209989, the target torque calculation unit 2 and the target voltage calculation unit 4 perform proportional / integral / differential calculations by the PID regulators 15, 18, and 19. Depending on, a PI controller that performs only proportional / integral may be used.
Next, the electrical configuration of the position estimation unit 11 will be described with reference to FIG. In general, the voltage / current equation (electrical equivalent equation) on the dq coordinate axis of the salient pole motor 12 is expressed by the following equations (1) and (2).

The motor model current calculation unit 20 has an equivalent model expression represented by the expression (3) in which the voltage / current equation of the expression (1) is expressed by a discrete value system of the sample period T, and based on the equivalent model expression Estimated currents Idm and Iqm are calculated. This equivalent model formula uses a motor constant at a predetermined temperature, and is stored in advance in a memory means such as a semiconductor memory element such as an EEPROM. The sample period T is set equal to the carrier wave period of the PWM signal described above.

The current deviation calculation unit 21 uses the subtractors 22 and 23 to estimate the currents output by the αβ / dq conversion unit 10 from the estimated currents Idm (n) and Iqm (n) output from the motor model current calculation unit 20, respectively. By subtracting Id (n) and Iq (n), current deviations ΔIdm (n) and ΔIqm (n) are calculated.

Here, when the angle error of the estimated axis with respect to the dq axis coordinate system is small, the current deviation ΔIdm (n) is approximately proportional to the angle error, and the current deviation ΔIqm (n) is approximately the estimated speed electromotive force em. Is proportional to the error. Therefore, the estimated rotational speed ωm is obtained while being corrected by feedback control so that the current deviation ΔIdm (n) converges to zero.
The q-axis integral regulator 24 converges the current deviation ΔIqm (n) to 0 to calculate the estimated speed electromotive force em (n) used in the above equation (2). The estimated speed electromotive force em (n) calculated here is divided by the speed electromotive force constant KE in the divider 25. On the other hand, the d-axis proportional controller 26, the integral controller 27, and the adders 28 and 29 calculate the estimated rotational speed ωm (n) by converging the current deviation ΔIdm (n) to zero. Then, the integrator 30 integrates the estimated rotational speed ωm (n) to obtain the estimated rotational position θm (n) of the rotor. Note that these rotational position estimation processes are also disclosed in detail in JP-A-2003-209989.

In the above description, the inverter device 1 excluding the inverter main circuit 7 constitutes the inverter control device 30, and the inverter control device 30 excluding the current detection unit 8 and the position estimation unit 11 is the PWM signal generating means. 31 is constituted.
These control functions are realized by software (program) such as a DSP (Digital Signal Processor) or a RISC (Reduced Instruction Set Computer) architecture microcomputer. The “processor” in claim 11 is a DSP. And a microcomputer (or CPU). The software is stored in a storage medium such as a ROM. If necessary, the software is stored in a storage medium such as a floppy (registered trademark) disk or a memory card, and the stored contents are rewritten into an EEPROM or the like. It is also possible to supply to a plurality of other inverter control devices 30 by writing.

  Next, the operation of the present embodiment will be described with reference to FIGS. 1 to 3, 7 and 8. FIG. FIG. 1 is a flowchart showing details of the control process at the time of starting the motor 12, and FIG. 2 is a timing chart showing changes in values in the control process. The inverter device 1 includes a target voltage calculation unit 4, a dq / αβ conversion unit 5, a PWM signal generation unit 6, an inverter main circuit 7, a motor current detection unit 8, a three-phase / two-phase conversion unit 9, an αβ / dq conversion. The frequency of the execution loop of the unit 10 and the position estimation unit 11 is set to 8 kHz (step S1). This is equivalent to the PWM signal generator 6 setting the carrier frequency to 8 kHz. Note that the carrier frequency 8 kHz is set higher than those because the carrier frequency in general inverter control is 3 kHz to 6 kHz.

Further, the current command value Idref input to the target voltage calculation unit 4 is constantly increased and the current command value Iqref is set to “0”. Further, the position information θm output from the position estimation unit 11 is set to a fixed value (step S1). Thereby, direct current excitation acts on the motor 12, and the rotor is fixed at an arbitrary position (see FIG. 2 (1), direct current excitation period).
In this state, after waiting for 3 seconds to pass (step S2, “YES”), the current command value Idref is fixed to a constant value, and the position information θm is changed at a constant frequency (step S3). Then, the motor 12 is forcibly commutated and the acceleration of the rotor is started. That is, as described above, in the method of estimating the rotational position of the rotor by calculation based on the electrical equivalent equation of the motor, the speed electromotive force is small due to the electrical error factor in the low-speed rotation region, and accurate estimation is difficult. Therefore, the rotor is accelerated to a speed at which position estimation can be accurately performed by forced commutation (see FIG. 2 (2), forced commutation period).

  After waiting for 0.2 seconds to pass in this state (step S4, “YES”), the position information θm output by the calculation result in the position estimation unit 11 is converted into the dq / αβ conversion unit 5 and the αβ / dq conversion. While permitting the input to the unit 10, the current command value Idref is lowered at a constant rate and the current command value Iqref is raised at a constant rate at a rate of change corresponding to the degree of acceleration of the rotor (step S5). At this stage, a closed loop of synchronous control is formed in which the output torque of the motor 12 is controlled by the current command value Iqref (see FIG. 2 (3), synchronous transition period).

  Then, when the current command value Idref becomes “0” and the current command value Iqref reaches a certain value, the state is maintained (step S6), and waits until a predetermined time elapses (step S7, “YES”, FIG. 2 (4)), initial synchronization period). Then, the angular velocity information ωm output by the position estimation unit 11 is permitted to be input to the target torque calculation unit 2, the target current calculation unit 3 is enabled, and the control frequency is reduced to 3 kHz (step S8). From this point of time, a transition is made to a steady control state where the estimation of the rotational position can be continued stably (see FIG. 2 (5)). The period (predetermined time) (1) to (4) shown in FIG. 2 corresponds to the start control period.

  Here, FIG. 7 shows the configuration of the compressor 51 as a model. That is, in the reciprocating compressor 51, the piston 42 inside the cylinder 41 is reciprocated by the rotational driving force of the motor 12. A suction pipe 43 and a discharge pipe 44 are connected to the upper end side of the cylinder 41, and a suction valve 45 and a discharge valve 46 are arranged at the respective boundaries. The suction valve 45 opens only in a direction in which the expanded refrigerant in the suction pipe 43 is sucked into the cylinder 41 when the piston 42 moves downward. On the other hand, the discharge valve 46 is opened only in a direction in which the piston 42 moves upward, compresses the refrigerant sucked into the cylinder 41, and discharges it to the discharge pipe 44 side.

  In this case, the reciprocating motion of the piston 42 is represented by the rotational phase (0 to 2π) of the motor 12 and taken on the horizontal axis, and the load on the motor 12 is taken on the vertical axis, as shown in FIG. As is apparent from FIG. 8, in the process in which the piston 42 moves upward and compresses the refrigerant, the load of the motor 12 gradually increases. When the pressure in the cylinder 41 and the pressure of the refrigerant in the discharge pipe 44 via the discharge valve 46 gradually approach and the former exceeds the latter, the discharge valve 46 opens, and the compressed refrigerant in the cylinder 41 is discharged. It is discharged to the tube 44 side. Therefore, at the moment when the discharge valve 46 is opened, the load on the motor 12 rapidly decreases. The maximum-minimum difference ΔP of the load is the differential pressure of the compressor 51.

  In the refrigeration cycle 50 of the refrigerator, the differential pressure is small at the time when cooling is started from room temperature, and the differential pressure gradually increases as the cooling in the refrigerator proceeds. Therefore, if the operation of the refrigeration cycle 50, that is, the operation of the compressor 51 is temporarily stopped to adjust the cooling temperature from the state in which the interior is sufficiently cooled, and a relatively short time has passed, The motor 12 is started from a state where the pressure is very large.

  In addition, as described above, the method of estimating the rotational position of the rotor by calculation based on an electrical equivalent equation has a situation in which accurate estimation is difficult in a low-speed rotation region, and the estimation becomes unstable. Therefore, conventionally, the restart is waited until the pressure difference between the suction and discharge drops to a level at which the motor can be started. However, “waiting for the pressure difference to drop” is equivalent to waiting for the temperature inside the chamber to rise once the cooling has progressed. It will be recooled. That is, as a result, the energy required for cooling is wasted.

  Then, as described in the above embodiment, the inventor of the present invention sets the PWM carrier frequency in the start control period to be higher than the frequency in the steady control state, so that the output torque in the low speed rotation region of the motor 12 is set. Was experimentally confirmed to be obtained. FIG. 3 shows the results of testing the present invention applied to a 400 L class refrigerator. The annual power consumption is about 260 kWh. Then, when a pressure sensor was attached to each of the suction side and the discharge side of the compressor, and the frequency of the PWM carrier wave was changed during the start-up control period, the differential pressure that could be restarted was measured.

  As shown in FIG. 3, when the frequency is the same 3 kHz as in the steady control state, the differential pressure that can be started is 0.2 Mpa, but when the frequency is increased to 5.5 kHz and 8 kHz, the differential pressure that can be started is It gradually increases to 0.3 Mpa and 0.4 Mpa. That is, a larger output torque for resisting the differential pressure is obtained. And in the case of frequency 8kHz, the energy-saving effect of the refrigerator became + 2.0%.

As described above, according to the present embodiment, the inverter control device 30 detects the current flowing through the motor 12 and estimates the rotational position θm of the rotor by calculating the current value by vector control in the position estimation unit 11. Then, based on the estimated rotational position, a multi-phase PMW signal that causes the inverter main circuit 7 that drives the motor 12 to output a pseudo sine wave voltage signal is generated and output. Then, the PMW signal generation means 51 sets the carrier frequency of the PWM signal to 8 kHz during the start control period in which the rotational position estimation in the position estimation unit 11 becomes unstable from the start of the start of the motor 12, and the start control period elapses. The carrier frequency is set to 3 kHz when the rotational speed of the motor 12 increases and the rotational position estimation in the position estimation unit 11 can be stably continued.
Therefore, the output torque of the motor 12 can be improved as compared with the prior art during the start control period in which the start load is high and the position estimation is unstable, and the motor 12 can be started easily. Since the carrier frequency is lowered in the steady control state, an increase in switching loss can be suppressed as much as possible.

  Since the inverter device 1 drives the reciprocating compressor 51 by the motor 12, it is extremely difficult when the motor 12 restarts from a state where the difference between the discharge pressure and the suction pressure is large in the compressor 51. It is valid. Furthermore, since the refrigeration cycle 50 of the refrigerator is configured by the compressor 51, the refrigeration cycle 50 can be restarted in a short time even when the refrigeration cycle 50 needs to be intermittent in the cooling control of the refrigerator. In addition, energy required for cooling at the time of restarting is not wasted as much as possible, so that energy saving can be further promoted.

The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible.
The carrier frequency in the start control period is not limited to 8 kHz, and may be appropriately set to a frequency higher than that in the steady control state so that an output torque required at the start can be obtained according to individual design.

  In the above embodiment, the start control period is estimated at least by the forced commutation period for forcibly commutating the motor 12, the synchronous transition period for starting the rotational position estimation by the position estimation unit 11, and the PMW signal generation means 51. And an initial synchronization period in which a closed loop of control based on the rotational position is formed. According to the inventors of the present invention, when setting the carrier frequency of the PWM signal higher than the steady control state, it has been experimentally confirmed that the same effect can be obtained even if such setting is performed only during the synchronization transition period. It was. In this case, the switching loss in the inverter main circuit 7 can be further reduced.

In the start control period, the DC excitation period may be provided as necessary. Further, if there is a period that becomes unnecessary according to different control methods, it may be deleted.
Further, the start control period for setting the carrier frequency of the PWM signal to be higher may be determined by appropriately setting a predetermined time from the start of the motor according to the individual control system.
Instead of CT, the current may be detected by a shunt resistor arranged on the lower arm side of the inverter main circuit 7.

Further, it is not always necessary to detect all three phases of the current, but at least two phases may be detected and the remaining one phase may be obtained by calculation.
The present invention is not limited to vector control, and can be applied as long as the rotational position of the rotor is estimated by arithmetic processing based on the detected motor current and the PWM signal is generated to perform switching control of the inverter main circuit.

You may apply not only to a refrigerator but to an air conditioner etc., for example.
Further, the present invention is not limited to a reciprocating type compressor, but is effective when applied to a configuration in which the starting load of the motor is relatively large.

The flowchart which shows one Embodiment at the time of applying this invention to the drive control apparatus of the compressor which comprises the refrigerating cycle incorporated in the refrigerator, and shows the control processing content at the time of the start of a motor FIG. 1 is a timing chart showing changes in values associated with the control process of FIG. The figure which shows the measurement result of the differential pressure which can be restarted when changing the frequency of the PWM carrier wave in the starting control period Functional block diagram showing the electrical configuration of the inverter device Functional block diagram showing the electrical configuration of the position estimation unit Configuration diagram of refrigeration cycle Diagram showing the structure of a reciprocating compressor The figure which shows the relationship between the piston position (phase) of a compressor and the load of a motor

Explanation of symbols

In the drawings, 1 is an inverter device (drive control device), 7 is an inverter main circuit, 8 is a motor current detection unit (current detection unit), 12 is a motor, 11 is a position estimation unit (position estimation unit), and 30 is inverter control. The apparatus, 31 is a PWM signal generating means, and 51 is a reciprocating compressor (reciprocating compressor).

Claims (11)

Current detection means for detecting the current flowing through the motor;
Position estimating means for estimating the rotational position of the rotor by calculating the current value;
PMW signal generating means for generating and outputting a multiphase PMW signal for outputting a pseudo sine wave voltage signal to an inverter main circuit for driving the motor based on the estimated rotational position,
The PMW signal generation means sets the carrier frequency of the PWM signal in the start control period until a predetermined time has elapsed from the start of the motor start to be higher than the carrier frequency in the steady control state after the period has elapsed. An inverter control device that is configured. The position estimation means estimates the rotational position of the rotor by calculating the current value based on the electrical equivalent equation of the motor,
2. The inverter control device according to claim 1, wherein the PMW signal generation means performs vector control based on the estimated rotational position. The start control period is a period in which the estimation of the rotational position in the position estimation means is unstable from the start of the motor start,
The inverter control device according to claim 1 or 2, wherein the steady control state is a state in which the estimation of the rotational position in the position estimating means can be continued stably as the rotational speed of the motor increases. The starting control period is at least
A forced commutation period in which the motor is forced to commutate;
A synchronous transition period in which estimation of the rotational position is started by the position estimating means;
The PMW signal generation means comprises an initial synchronization period in which a closed loop of control based on the estimated rotational position is formed,
4. The inverter control device according to claim 3, wherein the PMW signal generation unit sets the carrier frequency of the PWM signal higher than that in the steady control state only in the synchronization transition period.   A drive control device for a compressor, comprising the inverter control device according to any one of claims 1 to 4, wherein the reciprocating compressor is driven by a motor.   A refrigerating cycle is constituted by a reciprocating compressor, and the compressor driving control device according to claim 5 is provided. Detect the current flowing through the motor,
By calculating the current value, the rotational position of the rotor is estimated,
Based on the estimated rotational position, generates and outputs a multiphase PMW signal for causing the inverter main circuit that drives the motor to output a pseudo sine wave voltage signal,
An inverter control method, wherein a carrier frequency of a PWM signal in a start control period until a predetermined time elapses from a start time of starting of the motor is set to be higher than a carrier frequency in a steady control state after the lapse of the period.   8. The inverter control according to claim 7, wherein a rotational position of the rotor is estimated by calculating a current value based on an electrical equivalent expression of the motor, and vector control is performed based on the estimated rotational position. Method. The start control period is a period in which the estimation of the rotational position in the position estimation means is unstable from the start of the motor start,
The inverter control method according to claim 7 or 8, wherein the steady control state is a state in which the estimation of the rotational position in the position estimating means can be stably continued by increasing the rotational speed of the motor. The starting control period is at least
A forced commutation period in which the motor is forced to commutate;
A synchronous transition period for starting the estimation of the rotational position;
An initial synchronization period that forms a closed loop of control based on the estimated rotational position,
10. The inverter control method according to claim 9, wherein the carrier frequency of the PWM signal is set higher than that in the steady control state only during the synchronization transition period. A storage medium storing a program executed by a processor that controls the inverter,
Detect the current flowing through the motor,
By calculating the current value, the rotational position of the rotor is estimated,
Based on the estimated rotational position, to generate and output a multi-phase PMW signal for outputting a pseudo sine wave voltage signal to an inverter main circuit that drives the motor,
A computer program storing a carrier frequency of a PWM signal in a start control period until a predetermined time elapses from a start time of starting of the motor is set higher than a carrier frequency in a steady control state after the lapse of the period Storage media.