JP2012165582A - Motor controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-power-factor motor controller which can drive a synchronous motor with less vibration and low noise even for large load torque variations, and can suppress a direct current voltage increase due to regenerative energy.SOLUTION: In a motor controller 10, a reference value calculation section 29 calculates a first reference value corresponding to amplitude of a motor voltage on the basis of a phase difference between the motor voltage and a motor current flowing through a stator of a synchronous motor 2. A correction section 24 compares a line voltage between DC wiring HL and LL and a predetermined upper limit value, and outputs a second reference value that is a value obtained by adding a correction value according to the dimension of a load torgue to the first reference value when the line voltage is the upper limit value or less, and outputs a third reference value that is a value obtained by adding the correction value after being subjected to reduction to the first reference value when the line voltage exceeds the upper limit value. A control signal generation section 25 generates a control signal for controlling an inverter device 12 on the basis of the second or third reference value outputted from the correction section.

Description

  The present invention relates to a motor control device that drives and controls a synchronous motor, and more particularly to a motor control device that performs torque control of a synchronous motor.

  In synchronous motors used in compressors of air conditioners, it is difficult to provide sensors such as Hall elements to detect the position of the rotor (rotor) because the internal temperature of the compressor is high and high pressure. is there. For this reason, a sensorless drive type synchronous motor having no position sensor is generally used. For example, a motor control device described in Japanese Patent Application Laid-Open No. 2001-112287 (Patent Document 1) detects motor current areas in two phase periods with a motor voltage as a reference by using a motor current detection amplifier. Then, the motor control device of this document calculates the ratio of the detected motor current areas at two locations by the control microcomputer and uses this as phase difference information, controls the motor drive voltage based on this phase difference information, and determines the sine of a predetermined cycle By applying a wave to the motor coil, 180 ° drive including sine wave energization is enabled.

  In the motor control device of the above document, an AC current sensor for detecting a motor current of a specific phase among U, V, and W phases is provided to obtain phase difference information. Instead of directly detecting the motor current by the AC current sensor in this way, there is also a method of detecting the DC current flowing in the DC bus on the input side of the inverter circuit and estimating the motor current based on the detected value of the DC current. It is known (see, for example, JP-A-8-19263 (Patent Document 2)).

  Another problem of the synchronous motor for the compressor is that the load torque varies periodically because the pressure of the refrigerant gas changes for each of the suction, compression, and discharge processes. For this reason, in order to suppress the vibration and noise of the motor, it is necessary to perform torque control for changing the motor torque so as to match the fluctuation of the load torque. For example, in the technique described in Japanese Patent Application Laid-Open No. 2004-274841 (Patent Document 3), the duty ratio in a PWM (Pulse Width Modulation) type inverter circuit is set by a correction amount set in advance corresponding to the mechanical angle of the rotor. It is corrected. The correction amount at this time is determined according to the variation pattern of the load torque during one rotation of the motor.

  In recent years, in order to prevent power failure due to harmonic current, an example in which a power factor correction circuit is provided in an electronic device connected to a commercial power supply is increasing. In the case of a synchronous motor control device, in order to improve the power factor and reduce the size of the device, the capacitor provided on the output side of the full-wave rectifier circuit is significantly reduced in capacity (that is, full-wave rectification). Attempts have been made (without providing a large-capacitance capacitor for smoothing the output voltage of the circuit) (see, for example, JP-A-2002-51589 (Patent Document 4)).

  Japanese Patent Laid-Open No. 2005-124278 (Patent Document 5) prevents the parts of the inverter circuit from being destroyed by regenerative energy during high-speed rotation of the motor when the large-capacitance capacitor for smoothing is not provided. The technique for doing is disclosed. Specifically, the motor control device described in this document temporarily decreases the motor speed command value when the detected voltage value between the DC buses of the inverter circuit is equal to or higher than a preset threshold voltage.

JP 2001-112287 A JP-A-8-19263 JP 2004-274841 A JP 2002-51589 A JP 2005-124278 A

  When torque control is performed by the method described in Japanese Patent Application Laid-Open No. 2004-274841 (Patent Document 3), if the load torque fluctuation pattern deviates from a previously assumed pattern, the duty ratio of the PWM signal is corrected. Cannot be performed properly, so that a difference occurs between the load torque and the motor torque. As a result, the vibration and noise of the synchronous motor increase. In particular, when the motor torque is increased compared to the load torque, the regenerative energy increases as a result of the increase in the number of rotations of the motor. At this time, if a smoothing capacitor is not provided as described in JP-A-2002-51589 (Patent Document 4), an increase in regenerative energy cannot be absorbed by the smoothing capacitor. The voltage will rise greatly. As a result, a voltage exceeding the withstand voltage may be applied to the semiconductor switching element provided in the inverter circuit.

  The present invention has been made in consideration of the above problems. An object of the present invention is when a synchronous motor is driven by a motor control device that does not have a large-capacitance capacitor for smoothing, and the torque of a load connected to the synchronous motor varies with the rotation of the motor. Another object of the present invention is to provide a motor control device that can drive a synchronous motor with low vibration and low noise and suppress an increase in DC voltage due to regenerative energy.

  In one aspect, the present invention is a motor control device that drives and controls a synchronous motor connected to a load device, and includes a rectifier circuit, an inverter device, a voltage detection unit, a first reference value calculation unit, and a correction unit. And a control signal generator. Here, the load torque of the load device varies in accordance with the mechanical angle of the rotor of the synchronous motor. The rectifier circuit performs full-wave rectification on the input single-phase AC voltage. The inverter device converts the output voltage of the rectifier circuit into a multiphase AC voltage having an amplitude corresponding to the control signal, and outputs it as a motor voltage to the synchronous motor. A voltage detection part detects the line voltage between the DC wiring which connects a rectifier circuit and an inverter apparatus. The first reference value calculation unit calculates a first reference value corresponding to the amplitude of the motor voltage based on the phase difference between the motor voltage and the motor current flowing through the stator of the synchronous motor. The correction unit compares the line voltage with a predetermined upper limit value that is greater than or equal to the peak value of the single-phase AC voltage, and if the line voltage is less than or equal to the upper limit value, the correction corresponding to the mechanical angle of the synchronous motor When the second reference value, which is a value obtained by adding the value to the first reference value, is output and the line voltage exceeds the upper limit value, the reduced correction value is added to the first reference value. A third reference value is output. The control signal generation unit generates a control signal based on the second or third reference value output from the correction unit. The correction value is a value obtained by multiplying the first reference value by the first correction coefficient corresponding to the mechanical angle of the synchronous motor. The first correction coefficient is set in advance according to the magnitude of the load torque so that it becomes a positive value when the load torque is maximum during one rotation of the synchronous motor and becomes a negative value when the load torque is minimum. The

  Preferably, when the line voltage exceeds the upper limit value, the correction unit gradually reduces the first correction coefficient until the line voltage becomes equal to or lower than the upper limit value. Reduce gradually.

  Preferably, the first reference value calculation unit includes a second reference value calculation unit and a third reference value calculation unit. The second reference value calculation unit calculates the fourth reference value by performing arithmetic processing on the phase difference so that the phase difference between the motor voltage and the motor current matches a predetermined target phase difference. The third reference value calculation unit calculates the first reference value by correcting the fourth reference value according to the magnitude of the line voltage. The first reference value is a value obtained by multiplying the fourth reference value by the second correction coefficient. The second correction coefficient is smaller than 1 when the line voltage is larger than a predetermined voltage reference value that is less than the peak value of the single-phase AC voltage, and when the line voltage is smaller than the voltage reference value. Greater than 1. The second correction coefficient is smaller as the ratio of the line voltage to the voltage reference value is larger.

Preferably, the upper limit value is set in advance based on the breakdown voltage of the inverter device.
Preferably, the upper limit value is set in advance based on a line voltage detected in a state where the synchronous motor is stopped.

  Preferably, the motor control device further includes a capacitor provided between DC wirings connecting the rectifier circuit and the inverter device. Since the capacitance value of the capacitor is smaller than the value necessary for smoothing the output voltage of the rectifier circuit, the value of the line voltage depends on the absolute value of the single-phase AC voltage input to the rectifier circuit. fluctuate.

  According to the present invention, by correcting the first reference value corresponding to the amplitude of the motor voltage by the correction unit, the synchronous motor can be rotated with low vibration and low noise, and the DC voltage rises due to regenerative energy. Can be suppressed.

It is a functional block diagram which shows the structure of the air conditioner 1 by one Embodiment of this invention. It is a figure which shows the relationship between the load torque in 1 rotation of a motor, a motor torque, and a rotor angular velocity (when correction coefficient K = 0). It is a figure which shows the motor voltage amplitude at the time of correct | amending the amplitude reference value A with the correction coefficient K, and a motor torque. It is a figure which shows the relationship between the load torque in 1 rotation of a motor, a motor torque, and a rotor angular velocity (when an amplitude reference value is correct | amended with the correction coefficient K). It is a figure which shows the fluctuation pattern of the load torque of the compressor. It is a flowchart which shows the motor control procedure by the microcomputer 20 of FIG. It is a figure which shows the voltage waveform and current waveform which are observed in each part of the motor control apparatus 10 when the synchronous motor 2 is stopped. It is a figure which shows the voltage waveform and current waveform which are observed in each part of the motor control apparatus 10 when the synchronous motor 2 is operating (when the correction coefficient K is fixed to an initial set value). It is a figure which shows the voltage waveform and electric current waveform which are observed in each part of the motor control apparatus 10 when the synchronous motor 2 is operating (when the correction coefficient K is reduced according to the line voltage).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

[Configuration of air conditioner and motor control device]
FIG. 1 is a functional block diagram showing a configuration of an air conditioner 1 according to an embodiment of the present invention. Hereinafter, the air conditioner 1 will be described as an example, but the present invention can be applied to a device that uses a refrigeration cycle (heat pump cycle) such as a refrigerator.

  Referring to FIG. 1, an air conditioner 1 includes a synchronous motor 2, a compressor 3 as a load device connected to the synchronous motor 2, and a motor control device 10 that drives and controls the synchronous motor 2. The motor control device 10 converts a single-phase AC voltage received from an AC power source 4 such as a commercial power source into a three-phase AC voltage having a desired frequency and amplitude, and supplies it to a stator (stator) of the synchronous motor 2. . As a result, the synchronous motor 2 is driven at a variable speed.

  The compressor 3 driven by the synchronous motor 2 is a single rotary type compressor often used for an air conditioner or a refrigerator, for example. The feature of the single rotary compressor is that the structure is simple and the manufacturing cost is low, but the load torque fluctuation during one rotation of the motor is very large. In a single rotary compressor, a compression cycle of refrigerant suction, compression, and discharge is sequentially repeated during one rotation of the motor. Therefore, since the refrigerant is compressed immediately before the discharge, the load torque is increased. Immediately after the discharge, the refrigerant is discharged, so the load torque is reduced. Thus, the load torque of the single rotary compressor fluctuates in synchronization with the rotation of the synchronous motor (that is, corresponding to the mechanical angle during one rotation of the motor).

  The air conditioner 1 includes at least an indoor heat exchanger, an outdoor heat exchanger, an expansion valve, and a refrigerant pipe that connects them in addition to the configuration shown in FIG. By switching the four-way valve provided in the refrigerant pipe, the refrigerant flows in the order of the compressor, the outdoor heat exchanger, the expansion valve, the indoor heat exchanger, and the compressor when performing the cooling operation, and when performing the heating operation, the compressor, the indoor The refrigerant flows in the order of the heat exchanger, the expansion valve, the outdoor heat exchanger, and the compressor.

  Hereinafter, the configuration of the motor control device 10 will be described in detail. The motor control device 10 includes a rectifier circuit 11, an inverter circuit 12, a capacitor C 1, a voltage detection unit 13, a current sensor 14, an amplifier 15, and a microcomputer 20.

  The rectifier circuit 11 includes diodes D1 to D4, and full-wave rectifies the single-phase AC voltage received from the AC power supply 4.

  The inverter circuit 12 converts the output voltage of the rectifier circuit 11 into a three-phase AC voltage (U phase, V phase, W phase) and supplies it to the synchronous motor 2 to the stator winding. The inverter circuit 12 corresponds to the switching elements Qu, Qv, Qw, Qx, Qy, and Qz connected in a three-phase bridge, and these switching elements are respectively connected in parallel to the corresponding switching elements in the reverse bias direction. Including freewheel diodes Du, Dv, Dw, Dx, Dy, and Dz. In the inverter circuit 12 shown in FIG. 1, an IGBT (Insulated Gate Bipolar Transistor) is exemplified as the switching element. When the switching elements Qu to Qw and Qx to Qz are switched according to the PWM signal output from the microcomputer 20, the inverter circuit 12 outputs a three-phase AC voltage having an amplitude and a frequency according to the control signal to the synchronous motor 2. To do.

  The capacitor C1 is connected between the high voltage side DC wiring HL and the low voltage side DC wiring LL connecting the rectifier circuit 11 and the inverter circuit 12. The capacitor C1 is mainly for cutting off a carrier signal at the time of pulse width modulation (PWM) in the inverter circuit 12, and is not for smoothing the output voltage of the rectifier circuit 11. Therefore, the capacitance value of the capacitor C1 is considerably smaller than the value necessary for smoothing the output voltage of the rectifier circuit 11. The capacitance value of the capacitor C1 is, for example, 10 μF, which is about 1/100 of a smoothing capacitor for a conventional diode full-wave rectifier circuit. As a result, the voltage between the DC wires HL and LL during driving of the synchronous motor 2 depends on the absolute value of the input voltage of the rectifier circuit 11, that is, pulsates at a frequency twice that of the AC power supply 4. The maximum value of the voltage between the DC wirings HL and LL is 10 times or more the minimum value. Thus, by pulsating the voltage between the DC wirings HL and LL, the input current waveform to the rectifier circuit 11 can be brought close to a sine wave to improve the power factor.

  The voltage detector 13 detects a voltage (line voltage) between the DC wirings HL and LL. The detected line voltage is input to the microcomputer 20. For example, the voltage detection unit 13 includes a plurality of resistance elements (not shown) connected in series between the DC wirings HL and LL. The voltage divided by these resistance elements is input to the microcomputer 20 and converted into digital data by an A / D (Analog to Digital) converter (not shown).

  The current sensor 14 detects a current flowing in a stator winding of a specific phase (in the case of FIG. 1, U phase) among the U, V, and W phase stator windings of the synchronous motor 2. As the current sensor 14, a sensor constituted by a coil and a Hall element, a current transformer, or the like can be used. The signal detected by the current sensor 14 is amplified and offset added by the amplifier 15 and then input to the microcomputer 20 and converted into digital data by an A / D converter (not shown).

  The microcomputer 20 includes a CPU (Central Processing Unit), a RAM (Random-Access Memory), a ROM (Read-Only Memory), an A / D converter, and a D / A (Digital to Analog) converter. Not shown). The microcomputer 20 generates a PWM signal for controlling the inverter circuit 12 based on the signals detected by the voltage detector 13 and the current sensor 14. The generated PWM signal is converted into an analog signal by the D / A converter and then output to the inverter circuit 12.

  The speed control method of the synchronous motor 2 according to the present embodiment is a separate operation (speed open loop operation) method. That is, under the control of the microcomputer 20, the inverter circuit 12 applies a motor voltage having a forced excitation angular frequency corresponding to the rotational speed command value to the stator windings of each phase of the synchronous motor 2. At this time, the microcomputer 20 detects the phase difference between the motor voltage and the motor currents Iu, Iv, Iw flowing through the stator windings of each phase, and performs feedback control so that the detected phase difference becomes the target phase difference. . Such phase difference control does not directly detect the relative position between the rotor and the stator of the synchronous motor 2, but the phase difference and the relative position between the rotor and the stator are substantially proportional to each other, so the phase difference is controlled. By doing so, the relative position of the rotor-stator can be controlled indirectly. As a result, the motor can be energized at an appropriate timing for highly efficient driving of the synchronous motor 2.

[Details of motor control by microcomputer 20]
The microcomputer 20 shown in FIG. 1 functionally includes a phase difference control unit (amplitude reference value calculation unit) 21, a voltage correction unit 22, a mechanical angle detection unit 23, a torque control unit 24, and a PWM signal generation. Part 25. Each of these functional blocks is realized by the microcomputer 20 operating according to a program.

  The phase difference control unit 21 receives the motor voltage signal output from the PWM signal generation unit 25 and the motor current signal output from the current sensor 14 and receives an amount (phase difference information and the phase difference information) between these signals. And an amplitude reference value A corresponding to the amplitude of the motor voltage is calculated based on the phase difference information. Here, since the motor voltage signal is generated by the PWM signal generation unit 25, it is not necessary to directly detect the motor voltage of the specific phase of the synchronous motor 2 (the U phase in FIG. 1). The phase difference calculated based on the time difference between the zero cross point of the motor voltage signal and the zero cross point of the motor current signal may be used as phase difference information, or described in Japanese Patent Laid-Open No. 2001-112287 (Patent Document 1). The phase difference information may be obtained according to a method. In the latter method, the phase difference control unit 21 uses the motor current detected by the current sensor 14 to detect the area of the motor current in two phase periods with reference to the motor voltage, and the two motor currents. An area ratio is calculated and used as phase difference information.

  The phase difference control unit 21 calculates the amplitude reference value A by PI (proportional integration) control or the like so that the phase difference information calculated as described above matches the target phase difference information. The calculated amplitude reference value A is a constant value independent of the mechanical angle of the rotor of the synchronous motor 2. Here, as the target phase difference information, a value suitable for driving the synchronous motor 2 with high efficiency is determined in advance for each motor rotation condition (motor rotation speed or motor current amplitude) by experiments or simulations. It is done.

  The voltage correction unit 22 determines the degree of difference between the line voltage between the DC wirings HL and LL detected by the voltage detection unit 13 and a preset DC voltage reference value (difference between the line voltage and the DC voltage reference value). Or the ratio of the line voltage and the DC voltage reference value), the amplitude reference value A is corrected. The corrected amplitude reference value A ′ is smaller than the original amplitude reference value A when the line voltage is larger than the DC voltage reference value, and the original value when the line voltage is smaller than the DC voltage reference value. The value is larger than the amplitude reference value A. As a result, when the load torque is a constant value (that is, when the load torque does not change according to the mechanical angle), the amplitude of the three-phase AC voltage output from the inverter circuit 12 even when a smoothing large-capacity capacitor is not provided. Can be controlled to be constant. Here, the DC voltage reference value is set to a positive value less than the peak value of the single-phase AC voltage input to the rectifier circuit 11. For example, when the effective value of the single-phase AC voltage is 220V and the peak value is 311V, the DC voltage reference value is set to 280V.

Specifically, in the case of the present embodiment, the voltage correction unit 22 outputs a value (A ′ = α × A) obtained by multiplying the amplitude reference value A output from the phase difference control unit 21 by the correction coefficient α. . When the line voltage detected by the voltage detector 13 is Vd and the DC voltage reference value is Vs, the correction coefficient α is
α = Vs / (Vd + δ) (1)
Given by. In the above equation (1), δ is a minute term set to prevent α from overflowing when the line voltage Vd becomes zero. An upper limit value of α may be provided instead of the minute term δ, and may be set to the upper limit value of α when Vd is a predetermined value or less. According to the above equation (1), the correction coefficient α is smaller than 1 when the line voltage Vd is larger than the DC voltage reference value Vs, and the line voltage Vd (exactly Vd + δ) is smaller than the DC voltage reference value Vs. Greater than 1 when is small. The correction coefficient α decreases as the ratio of the line voltage Vd to the DC voltage reference value Vs (Vd / Vs) increases.

The mechanical angle detector 23 detects the current mechanical angle of the rotor. The relationship between the electrical angle θ and the mechanical angle Θ on the basis of the U-phase motor voltage is as follows when the mechanical angle 0 ° corresponds to the U-phase electrical angle 0 °:
Θ = θ / p (2)
It is represented by However, the number of poles of the motor is 2p (the number of pole pairs p). Therefore, in the case of a four-pole three-phase motor, a mechanical angle of 0 ° to 360 ° corresponds to an electrical angle of 0 ° to 720 °. At this time, in order to determine the mechanical position of the rotor based on the electrical angle, whether the rotor is in the range of mechanical angle 0 ° (electrical angle 0 °) to mechanical angle 180 ° (electrical angle 360 °) It is necessary to determine whether the angle is in the range of 180 ° (electrical angle 360 °) to mechanical angle 360 ° (electrical angle 720 °). The mechanical angle detection unit 23 detects the mechanical angle of the rotor by using the fluctuation of the amplitude of the U-phase motor current caused by the fluctuation of the load torque. Specifically, the mechanical angle detector 23 determines the mechanical position of the rotor by comparing the magnitudes of motor currents that are 180 degrees out of phase with the mechanical angle. Once the rotor mechanical angle is detected, the synchronous motor can be controlled only by the electrical angle.

  The torque control unit 24 further corrects the amplitude reference value A ′ corrected by the voltage correction unit 22 in accordance with the variation of the load torque during one rotation of the motor. Specifically, the amplitude reference value A ′ is corrected using the correction coefficient K set so as to change periodically corresponding to the mechanical angle Θ. The correction coefficient K is a periodic function expressed as a function F (Θ) of the mechanical angle Θ, the average value at one rotation of the motor is 0, and becomes a positive value when the load torque is maximum, and the load torque is minimum. When it is, it becomes a negative value. As a general tendency, the correction coefficient K increases as the load torque increases, and decreases as the load torque decreases.

However, the correction amount K × A ′ of the amplitude reference value A ′ by the correction coefficient K is determined in advance by the voltage between the DC wirings HL and LL detected by the voltage detector 13 according to the withstand voltage of the inverter circuit 12. If the upper limit is exceeded, it is reduced. That is, by using the parameter β (0 <β ≦ 1), the correction amount corresponding to the load torque is given by β × K × A ′. The parameter β is set to 1 in the initial state, and when the voltage between the DC wirings HL and LL (line voltage) exceeds the upper limit value, the parameter β is gradually reduced until the line voltage does not exceed the upper limit value. . Finally, the corrected amplitude reference value output from the torque control unit 24 to the PWM signal generation unit 25 is
(1 + β × K) × α × A (3)
Is given as follows. The reason why the amplitude reference value correction amount K × A ′ is reduced by the parameter β as described above is as follows.

  If the variation pattern of the load torque during one rotation of the motor deviates from a pattern assumed in advance (that is, a preset correction coefficient K), a difference occurs between the load torque and the motor torque. At this time, when the motor torque increases compared to the load torque, the rotational speed of the synchronous motor 2 increases, and as a result, the regenerative energy increases. Since the capacitor C1 provided in the motor control device 10 is not a large-capacitance capacitor for smoothing, the increase in regenerative energy cannot be absorbed by the capacitor C1. For this reason, the voltage between the DC wirings HL and LL rises. As a result, the switching elements Qu to Qw and Qx to Qz constituting the inverter circuit 12 may exceed the withstand voltage. Therefore, an upper limit value is provided for the voltage between the DC wirings HL and LL, and the correction coefficient K is adjusted by the parameter β so that the line voltage does not exceed the upper limit value.

  The upper limit value is a value that is equal to or greater than the peak value of the single-phase AC voltage input to the rectifier circuit 11, and is set to a value such that the voltage applied to each of the switching elements Qu to Qw and Qx to Qz is less than the withstand voltage. Is set. For example, when the effective value of the single-phase AC voltage input to the rectifier circuit 11 is 220 V (peak value 311 V) and the withstand voltage of the inverter circuit 12 is 500 V, the upper limit value is set to a value of 311 V or more and 500 V or less. . In consideration of control error and control delay of the microcomputer 20, it is desirable to set the upper limit value to a value sufficiently smaller than the withstand voltage (for example, 400V).

  The peak value of the single-phase AC voltage input to the rectifier circuit 11 is equal to the voltage between the DC wires HL and LL detected by the voltage detector 13 while the synchronous motor 2 is stopped. Therefore, this value may be stored in the memory of the microcomputer 20 and used as the upper limit value. That is, when the DC voltage detected by the voltage detector 13 while the motor is driven becomes larger than the DC voltage detected by the voltage detector 13 while the motor is stopped, the torque controller 24 corrects the correction coefficient K. May be reduced.

  The PWM signal generation unit 25 generates a PWM signal based on the frequency setting value (forced excitation angular frequency) of the synchronous motor 2 and the corrected amplitude reference value received from the torque control unit 24 to configure the inverter circuit 12. A control signal is output to the gate electrode of each switching element. Specifically, the PWM signal generation unit 25 generates a unit amplitude sine wave having a set frequency, and multiplies the generated unit amplitude sine wave by the corrected amplitude reference value expressed by Equation (3). To generate a motor voltage signal. The PWM signal generation unit 25 generates a PWM signal by comparing the generated motor voltage signal with a triangular carrier signal.

  In the above description, the phase difference control unit 21 corresponds to the second reference value calculation unit of the present invention, the voltage correction unit 22 corresponds to the third reference value calculation unit, and the phase difference control unit 21 and the voltage correction unit The portion 29 combined with 22 corresponds to the first reference value calculation unit of the present invention. The torque control unit 24 corresponds to the correction unit of the present invention, and the PWM signal generation unit 25 corresponds to the control signal generation unit. α × A corresponds to the first reference value of the present invention, (1 + βK) × αA corresponds to the second reference value (β = 1) and the third reference value (β <1), and the amplitude reference value A corresponds to the fourth reference value. The correction coefficient K corresponds to the first correction coefficient of the present invention, and α corresponds to the second correction coefficient.

[Specific example of motor control]
(When capacitor C1 is a large-capacity smoothing capacitor)
The motor control described above will be described more specifically with reference to voltage waveform diagrams and flowcharts shown in FIGS. First, as a premise of the present embodiment, the case where the capacitor C1 is a large-capacity smoothing capacitor will be described. In this case, α = β = 1 is set in Equation (3).

  FIG. 2 is a diagram illustrating a relationship among load torque, motor torque, and rotor angular velocity during one rotation of the motor. FIG. 2 shows the relationship when the motor voltage amplitude is constant (that is, when the correction coefficient K is always 0 regardless of the mechanical angle in the equation (3)). The solid line graph in the upper part of FIG. 2 shows the relationship between the load torque and the mechanical angle of the rotor, the broken line graph shows the relationship between the motor torque and the mechanical angle, and the dashed line graph shows the relationship between the angular velocity of the rotor and the mechanical angle. Show the relationship. The lower graph of FIG. 2 shows the relationship between the motor voltage amplitude and the mechanical angle.

  In the case of FIG. 2, the load torque fluctuates during one rotation of the motor, whereas the amplitude of the motor voltage is controlled to be constant, so that the motor torque has a constant value with respect to the mechanical angle. As a result, the rotational speed of the motor changes according to the load torque, and the rotor angular velocity vibrates as shown in FIG. Therefore, in order to control the angular velocity of the rotor to be constant, it is necessary to control the motor voltage amplitude so that the load torque and the motor torque are substantially equal.

  FIG. 3 is a diagram illustrating the motor voltage amplitude and the motor torque when the amplitude reference value A is corrected by the correction coefficient K. In FIG. 3, the correction coefficient K, the amplitude reference value, the motor voltage amplitude, and the motor torque during one rotation of the motor are shown in order from the top. The amplitude reference value A is corrected to (1 + K) × A by the sinusoidal correction coefficient K shown in FIG. Then, the motor voltage amplitude actually applied to the synchronous motor 2 is controlled by the corrected amplitude reference value, and the motor torque changes according to the motor voltage amplitude.

  FIG. 4 is a diagram illustrating a relationship among load torque, motor torque, and rotor angular speed during one rotation of the motor. FIG. 4 shows a case where the motor voltage amplitude is changed according to the load torque. The solid line graph in the upper part of FIG. 4 shows the relationship between the load torque and the mechanical angle of the rotor, the broken line graph shows the relationship between the motor torque and the mechanical angle, and the dashed line graph shows the relationship between the angular speed of the rotor and the mechanical angle. Show the relationship. The lower graph of FIG. 4 shows the relationship between the motor voltage amplitude and the mechanical angle.

  In the case of FIG. 4, the correction value K is used to correct the motor voltage amplitude reference value A, so that the motor torque matches the fluctuation of the load torque during one rotation of the motor. As a result, the angular velocity of the rotor is controlled to be substantially constant, so that vibration and noise of the synchronous motor 2 and the compressor 3 are suppressed.

(Regarding fluctuation pattern of load torque of compressor 3)
FIG. 5 is a diagram illustrating a variation pattern of the load torque of the compressor 3. In FIG. 5, the horizontal axis represents the rotor mechanical angle [degree], and the vertical axis represents the load torque [N · m]. As shown in FIG.
The load torque varies according to the mechanical angle. The reason for this is that the pressure of the refrigerant gas changes for each of the suction, compression, and discharge processes during one rotation of the motor. The load torque increases in the compression process, and the load torque decreases in the discharge process. Furthermore, the maximum value of the load torque varies depending on conditions such as the suction pressure value, the discharge pressure value, and the refrigerant flow rate. In the example shown in FIG. 5, the maximum value of the load torque increases in the order of A to D, and the mechanical angle corresponding to the maximum value of the load torque changes as the maximum value of the load torque increases.

  As described above, when the variation pattern of the load torque changes according to the operating condition of the compressor, the motor torque is matched with the load torque in the control using the preset correction coefficient K (K = F (Θ)). I can't. As a result, when the motor torque is larger than the load torque, the motor rotation speed is increased and the regenerative current is also increased. As described with reference to FIG. 1, when the small-capacitance capacitor C1 is provided, the increase in the regenerative current cannot be absorbed, so the voltage between the DC wirings HL and LL rises and the withstand voltage of the inverter circuit 12 is increased. Will be exceeded. In order to deal with the problem of the DC voltage rise, the torque control unit 24 of the present embodiment adjusts the correction coefficient K so that the voltage between the DC wirings HL and LL does not exceed a predetermined upper limit value. .

(When the capacitor C1 is a small-capacitance capacitor (this embodiment))
FIG. 6 is a flowchart showing a motor control procedure by the microcomputer 20 of FIG. Hereinafter, the motor control procedure by the microcomputer 20 will be described with reference to FIGS.

  It is assumed that the parameter β in the above equation (3) is initialized to β = 1 at the start of the control procedure of FIG. First, in step S <b> 1, the microcomputer 20 acquires a detected value of the motor current detected by the current sensor 14.

  In the next step S2, the microcomputer 20 (phase difference control unit 21) calculates an amount (phase difference information) representing the phase difference between the motor voltage and the motor current.

  In the next step S3, the microcomputer 20 (phase difference control unit 21) calculates the amplitude reference value A by performing PI calculation on the deviation between the calculated phase difference information and the target phase difference information.

  In next step S <b> 4, the microcomputer 20 acquires the voltage value between the DC wirings HL and LL detected by the voltage detection unit 13.

  In the next step S5, the microcomputer 20 (voltage correction unit 22) corrects the amplitude reference value A based on the ratio between the detected voltage between the DC wirings HL and LL and a predetermined DC voltage reference value. Specifically, the amplitude reference value A is multiplied by α calculated according to the above equation (1).

  In step S <b> 6, the microcomputer 20 (torque control unit 24) reads the correction coefficient K corresponding to the current mechanical angle Θ from a memory that stores a table indicating the relationship between the mechanical angle Θ and the correction coefficient K.

  In the next step S7, the microcomputer 20 (torque control unit 24) determines whether the value of the voltage (line voltage) between the DC wirings HL and LL detected by the voltage detection unit 13 exceeds a predetermined upper limit value. Determine whether. If the detected value of the line voltage exceeds the upper limit value (YES in step S7), the microcomputer 20 (torque control unit 24) changes the parameter β to a value that is reduced by 1% from the current value. (Step S8). Thereafter, the process proceeds to step S9. If the detected value of the line voltage is equal to or lower than the upper limit value (NO in step S7), the microcomputer 20 (torque control unit 24) does not change the parameter β to the current value and proceeds to the next step. Proceed to S9.

  In step S9, the microcomputer 20 (torque controller 24) further corrects the amplitude reference value A using the correction coefficient K and parameter β corresponding to the current mechanical angle. Specifically, the microcomputer 20 (torque control unit 24) calculates the corrected amplitude reference value according to the above-described equation (3).

  In the next step S10, the microcomputer 20 (PWM signal generation unit 25) generates a PWM signal based on the corrected amplitude reference value and frequency setting value (forced excitation angular frequency) calculated in step S9. The generated PWM signal is output to the inverter circuit 12. Thereafter, the process returns to step S1, and steps S1 to S10 are repeated thereafter. While the state in which the detected value of the line voltage exceeds the upper limit value continues, the parameter β is gradually reduced in step S8, thereby correcting the amplitude reference value (ie, β × K × α × A). Will gradually shrink.

  FIG. 7 is a diagram illustrating a voltage waveform and a current waveform observed in each part of the motor control device 10 when the synchronous motor 2 is stopped. In FIG. 7, the waveform of the single-phase AC voltage input to the rectifier circuit 11 of FIG. 1, the waveform of the voltage (DC voltage) between the DC wirings HL and LL, and the DC wiring LL on the low voltage side are sequentially flowed from the top. The waveform of the direct current Id is shown. The effective value of the single-phase AC voltage is 220V, and the frequency is 50 Hz. A smoothed DC voltage of 311 V that is equal to the peak value of the single-phase AC voltage is generated between the DC wirings HL and LL.

  FIG. 8 is a diagram illustrating a voltage waveform and a current waveform observed in each part of the motor control device 10 when the synchronous motor 2 is operating. However, no upper limit is set for the voltage between the DC wirings HL and LL in FIG. 1, and the correction coefficient K remains at the initial setting and is not reduced by the parameter β. In FIG. 8, in order from the top, the time variation of the correction coefficient K, the waveform of the single-phase AC voltage input to the rectifier circuit 11 in FIG. 1, the waveform of the voltage (DC voltage) between the DC wirings HL and LL, and the low voltage The waveform of the direct current Id flowing through the side DC wiring LL is shown. The effective value of the single-phase AC voltage is 220V, and the frequency is 50 Hz. The rotation speed of the synchronous motor 2 at the time of measurement is 1500 rpm.

  Referring to FIG. 8, from time t1 to time t2, the correction coefficient K is an optimum value corresponding to the amount of change in the load torque during one rotation of the motor, so the voltage between the DC wirings HL and LL. (DC voltage) is substantially equal to the peak value (311 V) of the single-phase AC voltage. Since the capacitor C1 has a small capacity, almost all of the energy charged in the capacitor C1 is consumed by the synchronous motor 2, so that the DC voltage drops to almost 0 V at times t1 and t2.

  From time t3 to time t4, the correction coefficient K is not a value commensurate with the magnitude of the load torque during one rotation of the motor. As a result of the motor torque increasing above the load torque, a large regenerative current is generated (that is, the direct current Id in FIG. 1 flows in the reverse direction). Since this regenerative current cannot be absorbed by the small-capacitance capacitor C1, as a result, the DC voltage rises to about 420V in the vicinity of time t4, and rises by 100V or more compared to 311V when the correction coefficient K is optimum. If the voltage between the DC wirings HL and LL exceeds the withstand voltage of the inverter circuit 12, the switching elements Qu to Qw and Qx to Qz may be damaged.

  FIG. 9 is a diagram showing a voltage waveform and a current waveform observed in each part of the motor control device 10 when the synchronous motor 2 is in operation. However, an upper limit UL (311 V in the case of FIG. 9) is set to the voltage between the DC wirings HL and LL in FIG. 1, and the magnitude of the correction coefficient K is adjusted by the parameter β. In FIG. 9, in order from the top, the time variation of the corrected correction coefficient β × K, the waveform of the single-phase AC voltage input to the rectifier circuit 11 in FIG. 1, and the voltage (DC voltage) between the DC wirings HL and LL. A waveform and a waveform of the DC current Id flowing through the DC wiring LL on the low voltage side are shown. The effective value of the single-phase AC voltage is 220V, and the frequency is 50 Hz. The rotation speed of the synchronous motor 2 at the time of measurement is 1500 rpm.

  Referring to FIG. 9, since correction coefficient K is corrected by parameter β so that the DC voltage does not exceed upper limit UL, the generation of line current (negative DC current Id) is suppressed, and as a result, DC voltage Is suppressed below the upper limit UL.

  As described above, according to the motor control device of the present embodiment, the correction coefficient K is reduced so that the voltage detection value by the voltage detection unit 13 does not exceed the predetermined upper limit value UL. While maintaining the rotation of the synchronous motor, an increase in DC voltage due to regenerative energy can be suppressed.

[Modification]
In the motor control device 10 shown in FIG. 1, the motor current of a specific phase (U phase) among the U, V, and W phases is directly detected using the AC current sensor 14 in order to obtain phase difference information. A resistance element is inserted in the low-voltage side DC wiring LL in FIG. 1 in place of the AC current sensor 14, and the DC current Id is detected by the resistance element, so that it is described in JP-A-8-19263 (Patent Document 2). The motor current of each phase can also be estimated by a method similar to the method. Specifically, based on the PWM signal generated by the PWM signal generation unit 25, the change amount of the direct current value Id immediately before and immediately after each switching element constituting the inverter circuit 12 is switched is obtained. Based on this, the motor currents Iu, Iv, Iw are estimated.

  The embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Air conditioner, 2 Synchronous motor, 3 Compressor, 4 AC power supply, 10 Motor control apparatus, 11 Rectifier circuit, 12 Inverter circuit, 13 Voltage detection part, 14 Current sensor, 15 Amplifier, 20 Microcomputer, 21 Phase difference control Unit, 22 voltage correction unit, 23 mechanical angle detection unit, 24 torque control unit, 25 PWM signal generation unit, C1 capacitor, HL, LL DC wiring.

Claims (6)

A motor control device that drives and controls a synchronous motor connected to a load device,
The load torque of the load device varies according to the mechanical angle of the rotor of the synchronous motor,
The motor control device
A rectifier circuit for full-wave rectification of the input single-phase AC voltage;
An inverter device that converts the output voltage of the rectifier circuit into a multiphase AC voltage having an amplitude according to a control signal and outputs it as a motor voltage to the synchronous motor;
A voltage detector for detecting a line voltage between DC wirings connecting the rectifier circuit and the inverter device;
A first reference value calculation unit that calculates a first reference value corresponding to the amplitude of the motor voltage based on a phase difference between the motor voltage and a motor current flowing through the stator of the synchronous motor;
The line voltage is compared with a predetermined upper limit value that is a value equal to or higher than the peak value of the single-phase AC voltage, and when the line voltage is equal to or lower than the upper limit value, it corresponds to the mechanical angle of the synchronous motor. A second reference value that is a value obtained by adding a correction value to the first reference value is output, and when the line voltage exceeds the upper limit value, the reduced correction value is used as the first reference value. A correction unit that outputs a third reference value that is a value added to the value;
A control signal generation unit that generates the control signal based on the second or third reference value output from the correction unit;
The correction value is a value obtained by multiplying the first reference value by a first correction coefficient corresponding to a mechanical angle of the synchronous motor,
The first correction coefficient has a value that is positive when the load torque is maximum during one rotation of the synchronous motor and negative when the load torque is minimum. A motor control device that is preset in accordance with this.   When the line voltage exceeds the upper limit value, the correction unit gradually reduces the first correction coefficient until the line voltage becomes equal to or lower than the upper limit value. The motor control device according to claim 1, wherein the motor control device is gradually reduced. The first reference value calculation unit includes:
A second reference value calculation unit for calculating a fourth reference value by performing arithmetic processing on the phase difference so that a phase difference between the motor voltage and the motor current matches a predetermined target phase difference; ,
A third reference value calculation unit that calculates the first reference value by correcting the fourth reference value according to the magnitude of the line voltage,
The first reference value is a value obtained by multiplying the fourth reference value by a second correction coefficient,
The second correction coefficient is smaller than 1 when the line voltage is larger than a predetermined voltage reference value that is less than the peak value of the single-phase AC voltage, and the line voltage is smaller than the voltage reference value. Greater than 1 when is small,
The motor control device according to claim 1, wherein the second correction coefficient is smaller as a ratio of the line voltage to the voltage reference value is larger.   The motor control device according to claim 1, wherein the upper limit value is set in advance based on a withstand voltage of the inverter device.   The motor control device according to claim 1, wherein the upper limit value is set in advance based on the line voltage detected in a state where the synchronous motor is stopped. The motor control device further includes a capacitor provided between DC wirings connecting the rectifier circuit and the inverter device,
Since the capacitance value of the capacitor is smaller than a value necessary for smoothing the output voltage of the rectifier circuit, the value of the line voltage is the value of the single-phase AC voltage input to the rectifier circuit. The motor control device according to claim 1, which varies according to an absolute value.

Images