JP2019057979A - Motor control device and air conditioner - Google Patents

Abstract

To provide a motor control device capable of improving a power factor by a practical level, without using a large circuit component.SOLUTION: The motor control device according to an embodiment includes: a diode bridge circuit that rectifies AC voltage supplied from a single-phase AC power source; a valley-fill circuit having an input terminal which is connected to an output terminal of the diode bridge circuit; an inverter circuit that drives a motor by using the voltage supplied thereto via the valley-fill circuit; and a synchronization control unit that performs current control on the basis of a frequency that is two times of the frequency of the single-phase AC power source, in order to generate a conduction command to the inverter circuit.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a control device and an air conditioner including an inverter circuit that drives a motor.

  For example, in order to drive an AC motor such as a permanent magnet synchronous motor, it is necessary to convert a DC power source into three-phase AC power using an inverter that is a power converter. A system using an inverter is equipped with a power supply device for obtaining DC power from a commercial AC power supply.

  As a circuit constituting a power supply device that obtains direct current from alternating current, for example, a diode rectifier circuit, a power factor correction circuit, so-called PFC or the like is generally known. The diode rectifier circuit rectifies the AC voltage and converts it into a DC voltage. Since the voltage rectified by the diode rectifier fluctuates greatly similarly to the AC voltage, a smoothing capacitor is connected to smooth the voltage.

  However, in the above configuration, since the diode conducts only when the AC voltage is higher than the smoothing capacitor in the rectifier, the waveform of the current flowing from the AC power supply to the rectifier has an amplitude only near the peak of the AC voltage. The rate gets worse. Therefore, the power factor is improved by connecting the PFC circuit between the diode rectifier circuit and the smoothing capacitor. The DC power thus obtained is supplied to the inverter, and the motor is driven by controlling the three-phase AC current. Patent Document 1 shows an example of another technique for improving the power factor when a diode rectifier is used.

  However, when a PFC circuit is applied, there is a problem that the circuit becomes large due to a magnetic component such as a reactor. On the other hand, as shown in Non-Patent Document 1, for example, a system called an electrolytic capacitor-less inverter using a small-capacity film capacitor has been proposed in place of the DC electrolytic capacitor for smoothing. In this method, since the voltage of the DC section fluctuates at twice the frequency of the system AC voltage, the control of changing the motor output at the above double frequency is applied to improve the conduction angle of the diode bridge, and the current waveform is changed. The power factor is improved by approaching a sine wave.

2000 Annual Meeting of the Institute of Electrical Engineers of Japan Vol. 4, p1591, Isao Takahashi, Nagaoka University of Technology, “Inverter control method for PM motor with diode rectifier with high input power factor”

In the circuit configuration of Non-Patent Document 1, the power factor can be improved without a reactor necessary for a large electrolytic capacitor or a PFC circuit. However, since it is difficult to control the output of the motor, there is a problem that it is difficult to improve the power factor at a practical level that satisfies standards such as IEC61000-3-2, that is, to reduce current harmonics.
Therefore, a motor control device and an air conditioner that can improve the power factor at a practical level without using large circuit components are provided.

The motor control device of the embodiment includes a diode bridge circuit that rectifies an AC voltage supplied from a single-phase AC power supply,
A valley fill circuit having an input terminal connected to the output terminal of the diode bridge circuit;
An inverter circuit that drives the motor by a voltage supplied through the valley fill circuit;
In order to generate an energization command to the inverter circuit, a synchronization control unit that performs current control based on the double frequency of the single-phase AC power supply frequency is provided.

Functional block diagram showing the configuration of the motor control device according to the first embodiment Diagram explaining basic operation of valley fill circuit (1) Diagram explaining basic operation of valley fill circuit (2) Signal waveform diagram explaining basic operation of valley fill circuit The figure which shows the waveform of _AC voltage V _AC Figure showing the waveform of the power supply current I _AC when only electrolytic capacitors are used The figure which shows the waveform of power supply current I _AC when the valley fill circuit is provided Figure Valais fill circuit showing a power supply current I _AC waveforms of adding a capacitor C3 and C4, resistors R2 The figure which shows the structure of a q-axis current command generation part The figure which shows the structure of a d-axis current command generation part Shows an AC voltage V _AC, the waveform in the case of applying the configuration of this embodiment Diagram showing the waveform of the same power supply current I _AC The figure which shows the waveform of the DC voltage _VDC The figure which shows the waveform of the q-axis current Iq Diagram showing the result of fast Fourier transform of the DC power supply current The figure which is 2nd Embodiment and shows the case where a motor drive control apparatus is applied to the compressor motor of an air conditioner

(First embodiment)
Hereinafter, a first embodiment will be described with reference to FIGS. FIG. 1 shows the configuration of the motor control device of this embodiment. The motor 1 is a three-phase permanent magnet synchronous motor, an induction motor, or the like. In this embodiment, the motor 1 is a permanent magnet synchronous motor. The single-phase AC power supply 2 supplies AC power to the entire apparatus, and is a 100V or 200V system. The diode bridge circuit 3 is connected to the AC power source 2 and rectifies the bipolar AC and converts it into a unipolar DC.

  A valley fill circuit 5 is connected between the positive power supply line 4p and the negative power supply line 4n connected to the positive terminal and the negative terminal of the diode bridge circuit 3, respectively. Between the negative power supply line 4n and the positive power supply line 4p, a first series circuit 6 including a first diode D1 and a first capacitor C1 in the forward direction, a second capacitor C2 and a second diode D2 in the forward direction are provided. The second series circuit 7 is connected. A third series circuit 8 including a first resistor R1 and a forward third diode D3 is connected between the common connection points of the first series circuit 6 and the second series circuit 7.

  Further, a fourth series circuit 9 including a third capacitor C3 and a fourth capacitor C4 is connected between the positive power line 4p and the negative power line 4n. A second resistor R <b> 2 is connected between one end of the AC power supply 2 and a common connection point of the fourth series circuit 9. The above constitutes the valley fill circuit 5. The first to fourth capacitors C1 to C4 are all electrolytic capacitors. The valley fill circuit 5 adjusts the conduction amount of the diode bridge circuit 3 and improves the power factor by adjusting the charge amounts of the first and second capacitors C1 and C2, which are smoothing capacitors in the DC section.

  An inverter circuit 10 is connected to the subsequent stage of the valley fill circuit 5. The inverter circuit 10 is configured by connecting, for example, six N-channel MOSFETs 11 serving as switching elements in a three-phase bridge connection. Each phase output terminal of the inverter circuit 10 is connected to one end of each phase winding of the motor 1.

  The current detector 12 is a shunt resistor, for example, and is inserted into the negative power supply line 4n between the valley fill circuit 5 and the inverter circuit 10. Instead of this configuration, a current detector may be disposed at each phase output terminal portion of the inverter circuit 10 or a shunt resistor may be disposed on the lower arm side of the inverter circuit 10. The current detector 12 converts the detected current into a voltage signal and outputs the voltage signal to the control unit 21. The voltage detector 13 detects the AC voltage of the AC power supply 2 and outputs it to the control unit 21. The position sensor 14 detects the rotor rotational position of the motor 1 and outputs a position signal to the control unit 21.

  The current detection / coordinate conversion unit 22 in the control unit 21 extracts a three-phase current from the current detected by the current detector 12, and further converts them into currents Id and Iq of d and q axis coordinates used for vector control. To do. The speed / position detector 23 detects the motor speed ω and the rotational position θ from the position signal given by the position sensor 14. Alternatively, a configuration in which the position and speed are estimated from the voltage / current of the motor 1 without using the position sensor 14 may be adopted. The filter 24 is a low-pass filter that removes a frequency component twice the AC power supply frequency from the motor speed ω detected by the speed / position detector 23.

The speed control unit 25 generates the q-axis current command amplitude I _{qAmp by,} for example, _performing PI calculation on the difference between the speed command ω _ref input from the outside and the speed ω _LPF input from the filter 24. The q-axis current command amplitude I _qAmp corresponds to a q-axis current control parameter. The power supply phase detector 26 detects the AC power supply phase θ _AC from the AC voltage input by the voltage detector 13. q-axis current command generator 27, a power supply phase theta _AC, and generates a q-axis current command I _Qref and a q-axis current command amplitude I _Qamp. The speed control unit 25, the power supply phase detection unit 26, and the q-axis current command generation unit 27 constitute a synchronization control unit 28.

The d-axis current command generation unit 29 generates a d-axis current command value I _dRef to be given when executing field weakening control from the DC voltage V _DC and the voltage amplitude V _{dq of the} dq axis. The current control unit 30 generates dq axis voltage commands Vd, Vq from the input dq axis current commands I _dRef , I _qAm and the currents Id, Iq input from the current detection / coordinate conversion unit 22. The modulation control unit 31 outputs the dq axis voltage commands Vq, Vd to the three-phase switching signals U +, U−, V +. The signals are converted into V−, W +, and W−, and are output as gate signals to the FETs 11 constituting the inverter circuit 10.

Next, the operation of this embodiment will be described. First, the basic operation of the valley fill circuit 5 will be described with reference to FIGS. In order to simplify the description, the third and fourth capacitors C3 and C4 and the first and second resistors R1 and R2 are not shown. As shown in FIG. 2, when the AC voltage V _AC is positively or negatively large, the first and second capacitors C1 and C2 are charged by the voltage V _AC . At this time, the first and second diodes D1 and D2 are turned off, and the third diode D3 is turned on. At the same time, electric power is supplied to the motor 1 side which is a load. At this time, the DC voltage has the same magnitude as the value obtained by rectifying the _AC voltage VAC.

Since the first and second capacitors C1 and C2 are charged in a state of being connected in series via the third diode D3, the inter-terminal voltages Vc1 and Vc2 of the capacitors C1 and C2 are expressed by the equation (1) and FIG. As shown in FIG. 4, it becomes (√2) / 2 times the effective value V _ACrms of the power supply voltage V _AC . This period is referred to as a first period.

Next, when the magnitude of the _AC voltage V _AC decreases and falls below the voltage of the expression (1) that is the charging voltage of the first and second capacitors C1 and C2, the diode bridge circuit 3 is turned off, and the valley fill circuit 5 is further turned off. The first and second diodes D1 and D2 are turned on, and the third diode D3 is turned off. As a result, the voltages Vc1 and Vc2 charged in the first and second capacitors C1 and C2 are supplied to the load side as shown in FIG. This period is referred to as a second period. As a result, the DC voltage V _DC becomes a constant value equal to the charged capacitor voltages Vc1 and Vc2, as shown in FIG.

  During the first period, power is supplied from the AC power source 2 to the load via the diode bridge circuit 3. If the load is an AC load synchronized with the AC power source 2, the power factor of the AC power source 2 is assumed. Becomes higher. In addition, the charging currents to the capacitors C1 and C2 that are generated simultaneously during this period cause the power factor to decrease, but the charging current is limited by the first resistor R1 connected in series to the third diode D3. Can suppress the decrease in power factor.

During the second period, since power is supplied from the charged capacitors C1 and C2 to the load, the diode bridge circuit 3 does not conduct, the power supply current becomes zero, and the power factor becomes zero. However, considering one cycle of the AC power supply, most of the electric power is supplied during the first period in which the diode bridge circuit 3 is conducting, so the power factor over one cycle is improved. Further, it is possible to supply power to the load while the power supply voltage _VAC is decreasing.

FIG. 5 shows the waveform of the _AC voltage V _AC , and FIG. 6 shows the waveform of the power source current I _AC when only the electrolytic capacitor is used. Since a current flows only for a short period when the diode of the diode bridge circuit 3 is conductive, many power supply harmonics are included and the power factor is lowered. FIG. 7 shows a case where the valley fill circuit 5 is provided. The increase in the conduction angle of the diode reduces the harmonics of the power supply current and improves the power factor. Figure 8 is a further third capacitor and the fourth capacitor C3 and C4, are configured by adding a second resistor R2, improved distortion that occurred in the vicinity of the zero cross point the supply voltage V _AC, further harmonic reduction doing.

Next, the control unit 21 will be described. In general motor control, a current command value is determined based on a speed command value, a voltage command value is generated based on the detected motor current, and a switching signal is generated by the modulation control unit 31. The motor control by the control unit 21 of the present embodiment is different from the normal control because when the power supply voltage _VDC fluctuates greatly, the power factor of the power supply is improved by controlling the output of the motor 1 in accordance with the fluctuation. It is a point to do.

Specifically, sin ² calculation is performed on the current command value I _qAmp obtained by the speed control unit 25 using the phase θ _AC obtained by the power supply phase detection unit 26, and the q-axis current command value I _qRef is _calculated . Generate. FIG. 9 shows the configuration of the q-axis current command generation unit 27. In square operation unit 27a, performs an operation "sin ² theta _AC", and generates a q-axis current command value I _Qref by multiplying the calculation result and the current command value I _Qamp in the multiplier 27b. Then, by controlling the q-axis current Iq by the current control unit 30 based on the command value I _qRef , the motor output is changed in a sine wave _shape , and the power factor is improved in synchronization with the change of the power source. The result of the calculation “sin ² θ _AC ” is (1−cos 2θ _AC ) / 2, but the phase is adjusted as appropriate.

Further, the d-axis current command generation unit 29 performs field-weakening control so that the motor output voltage V _dq does not exceed the dynamically changing DC voltage V _DC to generate a d-axis current command value I _dRef . The motor output voltage V _dq is obtained by calculating from the d, q axis voltages Vd, Vq according to the equation (2).

FIG. 10 shows the configuration of the d-axis current command generation unit 29. The subtractor 29a and the integrator 29b integrate and calculate the difference value between the DC voltage V _DC and the motor output voltage V _dq . “K _{i — AFR} ” shown in the integrator 29b is an integral gain. Since the d-axis current Id does not need to flow during a period in which the polarity is positive, the limiter 29c limits the maximum value to zero. Further, since the speed of the filter 24 used for the speed feedback value fluctuates as the motor output fluctuates due to the influence of the power supply frequency, the influence of the power is not reflected on the q-axis current command value I _qRef. The frequency twice the frequency is removed.

FIG. 11 is a diagram showing the waveform of the _AC voltage V _AC when the configuration of this embodiment is applied, FIG. 12 is a diagram showing the waveform of the power supply current I _AC , and FIG. 13 is the waveform of the DC voltage _VDC. FIG. 14 and FIG. 14 are diagrams showing the waveform of the q-axis current Iq. FIG. 15 shows the result of FFT and fast Fourier transform of the power supply current, and the level of the harmonic component is within the standard of IEC61000-3-2.

  As described above, according to the present embodiment, the diode bridge circuit 3 that rectifies the AC voltage supplied from the AC power supply 2, the valley fill circuit 5 whose input terminal is connected to the output terminal of the diode bridge circuit 3, An inverter circuit 10 that drives the motor 1 with a voltage supplied via the fill circuit 5 and a synchronous control unit that performs current control based on a frequency twice the AC power supply frequency in order to generate an energization command to the inverter circuit 10 28. Thereby, it is possible to eliminate the influence of the power supply frequency generated in the voltage rectified by the diode bridge circuit 3, to improve the power factor, and to reduce the harmonic component.

Then, by providing the valley fill circuit 5 with the first resistor R1 and the second resistor R2, it is possible to limit the charging current to the capacitors C1 and C2 and suppress the decrease in the power factor. Further, it is possible to reduce harmonics and improve the distortion generated in the vicinity of the zero cross point the supply voltage V _AC.

Further, a speed / position detector 23 for detecting the rotational speed ω of the motor 1 and a speed control for generating a q-axis current command amplitude I _qAmp based on the difference between the given speed command value ω _ref and the rotational speed ω. Unit 5 and a vector control unit that detects a current supplied to motor 1 and performs vector control. Synchronous control unit 28 converts q-axis current command value I _qRef used for vector control to AC power supply It is generated by calculating the double frequency and the q-axis current command amplitude I _qAmp . Thereby, current control can be applied to vector control based on the double frequency.

(Second Embodiment)
FIG. 16 is a second embodiment, and shows a case where the motor control device of the first embodiment is applied to a compressor motor of an air conditioner. The compressor 42 constituting the heat pump system 41 is configured by accommodating the compression unit 43 and the motor 44 in the same iron hermetic container 45, and the rotor shaft of the motor 44 is connected to the compression unit 43. The compressor 42, the four-way valve 46, the indoor heat exchanger 47, the pressure reducing device 48, and the outdoor heat exchanger 49 are connected to form a closed loop by a pipe serving as a heat transfer medium flow path. The compressor 42 is, for example, a rotary compressor, and the motor 44 is, for example, a three-phase IPM (Interior Permanent Magnet) motor. The motor 44 is a brushless DC motor. The air conditioner 40 includes the heat pump system 41 described above.

  During heating, the four-way valve 46 is in a state indicated by a solid line, and the high-temperature refrigerant compressed by the compression unit 43 of the compressor 42 is supplied from the four-way valve 46 to the indoor heat exchanger 47 to condense, and then the decompression device. The pressure is reduced at 48 and the temperature becomes low and flows to the outdoor heat exchanger 49 where it evaporates and returns to the compressor 42. On the other hand, at the time of cooling, the four-way valve 46 is switched to a state indicated by a broken line. For this reason, the high-temperature refrigerant compressed by the compression unit 43 of the compressor 42 is supplied from the four-way valve 46 to the outdoor heat exchanger 49 to condense, and is then depressurized by the decompression device 8 to become a low temperature. It flows to the heat exchanger 47 where it evaporates and returns to the compressor 42. The indoor and outdoor heat exchangers 47 and 49 are blown by the fans 50 and 51, respectively, and the heat exchange between the heat exchangers 47 and 49 and the indoor air and outdoor air is efficient. It is structured to be performed well. The motor 44 is driven and controlled by the motor drive device of the first embodiment.

  According to the second embodiment configured as described above, the motor 44 of the compressor 42 constituting the heat pump system 41 in the air conditioner 40 is driven and controlled by the motor drive control device of the embodiment, so that the air conditioner The operating efficiency of the machine 40 can be improved.

(Other embodiments)
The resistance elements R1 and R2 may be provided as necessary.
The switching element is not limited to a MOSFET, and other wide gap semiconductors such as IGBT, power transistor, SiC, and GaN may be used.
You may apply not only to an air conditioner but to other products.
Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  In the drawings, 1 is a motor, 2 is an AC power supply, 3 is a diode bridge circuit, 5 is a valley fill circuit, 6 to 9 are first to fourth series circuits, 10 is an inverter circuit, 12 is a current detector, and 13 is a voltage. Detector, 14 is a position sensor, 21 is a control unit, 23 is a speed / position detection unit, 25 is a speed control unit, 28 is a synchronization control unit, 40 is an air conditioner, D1 to D3 are first to third diodes, C1 to C4 denote first to fourth capacitors.

Claims (4)

A diode bridge circuit for rectifying an AC voltage supplied from a single-phase AC power supply;
A valley fill circuit having an input terminal connected to the output terminal of the diode bridge circuit;
An inverter circuit that drives the motor by a voltage supplied through the valley fill circuit;
A motor control device comprising: a synchronous control unit that performs current control based on a frequency that is twice the single-phase AC power supply frequency in order to generate an energization command to the inverter circuit. The valley fill circuit includes a first capacitor having one end connected to a positive terminal of the diode bridge circuit and a first diode having an anode connected to a negative terminal of the diode bridge circuit. 1 series circuit,
A second series circuit in which a second diode having a cathode connected to the positive electrode side terminal and a second capacitor having one end connected to the negative electrode side terminal are connected in series;
A third series circuit comprising a first resistor and a third diode connected between the other end of the first capacitor and the other end of the second capacitor;
A fourth series circuit including a third capacitor and a fourth capacitor connected in series between the positive electrode side terminal and the negative electrode side terminal;
The motor control device according to claim 1, further comprising a common connection point of the third capacitor and the fourth capacitor, and a second resistor connected to one of the AC input terminals of the diode bridge circuit. A speed detector for detecting the rotational speed of the motor;
A speed control unit that generates a q-axis current control parameter based on a difference between a given speed command value and the rotation speed;
A vector control unit that detects a current supplied to the motor and performs vector control;
3. The motor according to claim 1, wherein the synchronous control unit generates a q-axis current command value used for the vector control by calculation of a double frequency of the single-phase AC power supply and the q-axis current control parameter. Control device. A motor constituting the compressor;
A motor control device according to any one of claims 1 to 3,
An air conditioner that performs an air conditioning operation by driving the compressor.

Images