JP2014138526A - Inverter control apparatus, and compressor equipped with the same - Google Patents

Abstract

A switching loss of an inverter circuit is reduced.
An inverter control device that controls the operation of a pulse width modulation type inverter that converts a direct current into a three-phase alternating current and supplies the same to a load. The inverter control device detects a current flowing through the load and determines the current based on the detected current. The phase is detected for each phase, and line modulation is performed based on the detected current phase. In a predetermined section including the maximum current or the minimum current in each phase, the pulse width modulation for the predetermined phase taking the maximum current or the minimum current is stopped, the voltage is fixed to a predetermined value, and the other two phases other than the predetermined phase Perform pulse width modulation only for.
[Selection] Figure 6

Description

  The present invention relates to an inverter control device and a compressor including the inverter control device.

  For example, devices such as an air conditioner and a refrigerator are equipped with a refrigeration cycle device. The refrigeration cycle apparatus includes a compressor for compressing a refrigerant, a condenser and an evaporator for exchanging heat between the refrigerant and air, an expansion valve, a four-way valve, and the like. The compressor includes a compressor main body and an electric motor for driving the compressor main body. For example, a permanent magnet synchronous motor is used as the electric motor. The rotation speed of the electric motor is variably controlled by an inverter.

  As a method of flowing a sine wave current to the motor, a three-phase line-to-line modulation method is known. In the three-phase line-to-line modulation method, a PWM signal is generated by comparing a triangular wave carrier signal with a sine wave that is an applied voltage of each phase. Furthermore, in order to reduce the loss in the inverter circuit, a two-phase line-to-line modulation method is also known. In the two-phase line modulation method, the voltage of a specific one phase in the three-phase voltage applied to the motor is constant, and the remaining two phases are maintained in order to keep the line voltage applied to the motor constant before and after the line modulation. Modulate between the lines.

  In the two-phase line-to-line modulation method, the voltage in the electrical angle 60 degree section of the phase that becomes the minimum voltage or maximum voltage in the fundamental wave is fixed to the inverter minimum output voltage or maximum output voltage. Thereby, in the phase where the voltage is fixed, there is no point where the carrier signal and the fundamental wave intersect, and switching is not performed. Therefore, in the two-phase line-to-line modulation method, the number of times of switching can be reduced as compared with the three-phase line-to-line modulation method, so that power loss in the inverter can be reduced.

  Here, in order to keep the line voltage applied to the motor constant before and after the line modulation, in the non-switching phase, the inverter minimum output voltage or maximum output voltage and the fundamental wave in the non-switching electrical angle 60 degree section This difference was added to other phases (Patent Document 1).

JP 2005-318702 A

  According to the conventional two-phase line-to-line modulation method, switching loss can be reduced as compared with the three-phase line-to-line modulation method. However, the conventional two-phase line-to-line modulation scheme is not necessarily the optimum scheme for reducing the switching loss, and there is room for improvement.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an inverter control device and a compressor including the inverter control device that can reduce the switching loss as compared with the conventional two-phase line-to-line modulation method.

  In order to solve the above problems, an inverter control device according to the present invention is an inverter control device that controls the operation of a pulse width modulation type inverter that converts a direct current into a three-phase alternating current and supplies the same to a load, Is detected for each phase based on the detected current, and line-to-line modulation is executed based on the detected phase of the current.

  In a predetermined section including the maximum current or the minimum current in each phase, the pulse width modulation for the predetermined phase taking the maximum current or the minimum current is stopped, the voltage is fixed to a predetermined value, and the other two phases other than the predetermined phase Perform pulse width modulation only for.

  According to the present invention, the switching loss can be reduced because the two-phase line-to-line modulation is performed according to the magnitude of the current flowing through each phase.

It is a circuit diagram in the case of using an inverter control apparatus for a compressor. It is a functional block diagram of an inverter control device. It is a functional block diagram of a PWM controller. It is explanatory drawing which shows the conventional 2 phase line modulation | alteration system as a comparative example. It is explanatory drawing which shows the relationship between the phase applied voltage, a carrier signal, and a PWM signal in the conventional 2 phase line-line modulation system as a comparative example. It is explanatory drawing which shows the relationship between the phase applied voltage, a carrier signal, and a PWM signal in the two-phase line modulation system by a present Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, the current detection means for detecting the phase current or DC current flowing in the motor as the load and the phase of the voltage are matched with a predetermined section having the largest current or the smallest current from the current detected by the current detection means. A phase adjustment unit to adjust, and a line modulation unit that sets a non-switching phase in the two-phase modulation based on current phase data from the phase adjustment unit. As a result, according to the present embodiment, the electrical angle 60 degree section of the non-switching phase in the two-phase modulation can be set to the phase with the least loss, and the switching loss of the inverter can be reduced, resulting in energy saving performance. Can be improved.

  Embodiments will be described with reference to FIGS. Below, the case where it applies to the compressor which drives an inverter is demonstrated.

  A compressor used in an air conditioner or a refrigerator includes a compressor main body 1, an electric motor 6 for driving the compressor main body 1, an inverter circuit 2 for giving a three-phase alternating current to the electric motor 6, A control device 3 for controlling the inverter circuit 2 and a current sensor 4 are provided. Here, the case where the electric motor 6 is a permanent magnet synchronous motor is taken as an example.

  The inverter circuit 2 includes a plurality of switching elements, an upper arm element 2A connected to the positive side of the DC power supply 5 and a lower arm element 2B connected to the negative side of the DC power supply 5 for each phase (U, V, W). Is provided. The upper arm element 2A and the lower arm element 2B of each phase are connected in series. In the drawing, the upper arm side is indicated as U +, V +, W +, and the lower arm side is indicated as U-, V-, W-.

  The inverter circuit 2 converts the voltage of the DC power source 5 into a pulse width modulated AC voltage and supplies it to the U-phase, V-phase, and W-phase three-phase stator windings of the synchronous motor 6, thereby 6 is rotated.

  The control device 3 as the “inverter control device” controls the rotational speed of the synchronous motor 6 by outputting a PWM signal to the inverter circuit 2 in accordance with the input speed command signal. The inverter circuit 2 is driven according to the PWM signal from the control device 3.

  The current sensor 4 as a current detection unit detects a motor current input from the DC power supply 5 to the inverter circuit 2 and sends the motor current to the control device 3.

  FIG. 2 shows a functional block configuration of the control device 3. The control device 3 feedback-controls the rotation speed of the synchronous motor 6 using the inverter circuit 2 and the current sensor 4. The control device 3 is configured as a computer device having, for example, a microprocessor, a memory, an I / O circuit, and the like, and a predetermined function is realized by the microprocessor executing a predetermined computer program stored in the memory. To do.

  The direct current Ish from the current sensor 4 is input to the current reproduction calculator 10. The current reproduction calculator 10 calculates a motor current detection value from the DC current Ish and outputs three-phase motor currents Iu, IV, and Iw.

  In the present embodiment, the motor current is detected by a direct current, but instead, the motor current may be detected by a current sensor using, for example, a Hall element. Furthermore, instead of detecting the direct current Ish, a configuration may be adopted in which the three-phase motor current is directly detected by a current sensor. In the case of a configuration in which the three-phase motor current is directly measured by a current sensor, the current reproduction calculator 10 can be omitted.

  The three-phase / two-axis converter 11 calculates voltage command signals Vdc * and Vqc * to be applied to the motor 6 by dq coordinate system vector control, and generates an inverter PWM signal. The three-phase / two-axis converter 11 generates a dc-axis current Idc and a qc-axis current based on the reproduced three-phase motor currents Iu, IV, Iw and phase information θdc estimated by a phase calculation unit 14 described later. Iqc is calculated and output.

  The axis error calculator 12 calculates and outputs an axis error Δθc using the dc axis voltage command value Vdc *, the qc axis command voltage value Vqc *, the dc axis current value idc, and the qc axis current value iqc.

  The low-pass filter 13 primarily filters the qc-axis current detection value Iqc output from the three-phase / 2-axis converter 11 and outputs a qc-axis current command value Iqc *.

  The phase calculation unit 14 calculates and outputs a control system phase θdc by integrating a motor rotation speed ωm estimated by a PLL controller 15 described later. The control system phase θdc is input to the 3-phase / 2-axis converter 11 and the 2-axis / 3-phase converter 18 described later.

  A PLL (Phase Locked Loop) controller 15 performs PI (Proportional Integral) control of a deviation between the axis error Δθc calculated by the axis error calculator 12 and the axis error command value Δθc * input from the axis error command generator 19. The estimated value ωm of the motor rotation speed is output by processing using a device.

  The d-axis current command generator 16 outputs 0 as the dc-axis current command value Idc *.

  The voltage command controller 17 uses the dc-axis current command value Idc *, the qc-axis current command value Iqc *, and the speed command value ω1 *, and uses the dc-axis voltage command value Vdc * and the qc-axis voltage command value Vqc *. Is calculated and output.

  The two-axis / three-phase converter 18 determines the three-phase voltage command values Vu * and Vv of the motor based on the dc-axis voltage command value Vdc *, the qc-axis voltage command value Vqc *, and the estimated phase information θdc. * And Vw * are calculated and output.

  The PWM controller 20 generates a PWM signal and inputs it to the inverter circuit 2, and includes a phase adjustment unit 21, a line modulation unit 22, and a PWM signal generation unit 23, which will be described later.

  FIG. 3 is a block diagram showing the configuration of the PWM controller 20. The phase adjusting unit 21 detects the phase PIu, PIv, PIw of the phase current based on the phase currents Iu, Iv, Iw, and outputs the detected phase PIu, PIv, PIw to the interline modulation unit 22.

  The line-to-line modulator 22 is based on the voltage commands Vu *, Vv *, and Vw * that are the outputs of the 2-axis / 3-phase converter 18, and the modulation factor limiter value, the two-phase modulation paste value, and the phase PIu of each phase current. , PIv, and PIw, the phase with the largest current or the phase with the smallest current is obtained. The line modulation unit 22 sets a section with an electrical angle of 60 degrees including the phase that becomes the maximum current or the minimum current as a predetermined section that is not switched, and the voltages Vu **, Vv **, and Vw ** after the two-phase modulation. Is output to the PWM signal generator 23. The PWM signal generation unit 23 inputs a PWM signal based on the signal from the line modulation unit 22 to the inverter circuit 2. As a result, the line voltage of the motor 6 is applied at a phase at which the switching loss is reduced most, and thus the motor 6 is operated with high efficiency.

  With reference to FIG. 4, a conventional modulation method will be described for comparison with the present embodiment. FIG. 4 (a) schematically shows the relationship between each phase applied voltage when the phase voltage is a sine wave, a triangular wave carrier signal (carrier wave signal), and a PWM signal.

  In general, when a sine wave current is passed through the synchronous motor 6, the output voltage of the inverter circuit 2 is a sine wave. For this purpose, switching is turned on at the point where the carrier signal indicated by the triangular wave and the signal waves Vu (solid line), Vv (dotted line), and Vw (finer dotted line) indicated by the sine wave that is the applied voltage for each phase intersect. -Generate a PWM signal to turn off in the PWM controller.

  A voltage is applied to the motor 6 by switching the six switching elements 2A and 2B constituting the inverter circuit 2 in accordance with the PWM signal. When the level of the PWM signal is Hi, the upper arm element 2A of the inverter circuit 2 is turned on, and when the level of the PWM signal is Low, the lower arm element 2B is turned on.

  Now, two-phase line-to-line modulation is a modulation between the remaining two-phase lines in order to keep a specific one-phase voltage constant and to keep the line voltage applied to the motor constant before and after the line-to-line modulation. Modulation method. FIG. 4B schematically shows the relationship among the three-phase motor applied voltage, the carrier signal, and the PWM signal after line modulation.

  In the two-phase line-to-line modulation, the voltage that crosses the carrier signal is fixed by fixing the voltage in the electrical angle 60 degree section of the phase that becomes the minimum voltage or maximum voltage in the fundamental wave at any time to the inverter minimum output voltage or maximum output voltage. To make a section that does not switch.

  In the two-phase line-to-line modulation, in order to keep the line voltage applied to the motor 6 constant before and after the line-to-line modulation, in the non-switching phase, the inverter minimum output voltage or maximum output voltage in the electrical angle 60 ° section where switching is not performed. And the difference between the fundamental wave and the fundamental phase. As a result, as shown in FIG. 4 (b), the applied voltage of each phase after two-phase line modulation appears to be greatly distorted from a sine wave, but the line voltage of the motor is sine regardless of before and after the line modulation. Keep the waves. FIG. 4C is an example of a PWM signal by two-phase line-to-line modulation.

  FIG. 5 shows the relationship between the fundamental wave of the applied voltage, the phase current, and the applied voltage after two-phase line modulation, excluding the carrier signal. In FIG. 5 and FIG. 6 described later, the upper sine wave indicates the fundamental wave of the applied voltage, the middle sine wave indicates the phase current, and the lower waveform indicates the applied voltage after two-phase line-to-line modulation.

  The effect of the two-phase line-to-line modulation according to this embodiment will be described with reference to FIG. In the present embodiment, as described above, the PWM controller 20 is provided with the phase adjustment unit 21, and the phase currents Iu, Iv, and Iw calculated by the current reproduction calculator 10 are input to the phase adjustment unit 21, The adjustment unit 21 outputs the phase PIu, PIv, PIw of each phase current.

  In the conventional two-phase line-to-line modulation shown in FIG. 5, the voltage in the electric angle 60 degree section of the phase that becomes the minimum voltage or the maximum voltage is fixed to the inverter minimum output voltage or the maximum output voltage. On the other hand, in the two-phase line modulation according to the present embodiment, as shown in FIG. 6, the voltage in the electrical angle 60 degree section of the phase that becomes the minimum current or the maximum current is changed to the phase of the inverter minimum output current or the maximum output current. Fix it.

  In the conventional method shown in FIG. 5, the section of the electrical angle of 60 degrees where the voltage of each phase is maximum or minimum is set as a section where switching is not performed, whereas in this embodiment, the electric current where the current of each phase is maximum or minimum is set. A section with a corner of 60 degrees is a section in which switching is not performed.

  Therefore, according to the present embodiment, the switching loss in the inverter circuit 2 can be further reduced as compared with the conventional method, and the electric motor 6 can be driven more efficiently.

  In addition, this invention is not limited to the Example mentioned above. A person skilled in the art can make various additions and changes within the scope of the present invention. For example, in the present embodiment, a permanent magnet synchronous motor is used as a motor. Instead, another synchronous motor such as a reluctance motor known as a synchronous reluctance motor having no permanent magnet or an induction motor is used instead. It may be used.

  1: compressor body, 2: inverter circuit, 2A, 2B: switching element, 3: control device, 4: current sensor, 5: DC power supply, 6: electric motor, 20: PWM controller, 21: phase adjustment unit, 22: Line modulation unit, PWM signal generation unit

Claims (6)

An inverter control device that controls the operation of a pulse width modulation type inverter that converts direct current into three-phase alternating current and supplies the load to a load,
Detecting the current flowing through the load;
Based on the detected current, the phase of the current is detected for each phase,
Perform line-to-line modulation based on the detected current phase,
Inverter control device. In a predetermined section including the maximum current or the minimum current in each phase, the pulse width modulation for the predetermined phase taking the maximum current or the minimum current is stopped, the voltage is fixed to a predetermined value, and other than the predetermined phase Perform pulse width modulation only for two phases,
The inverter control device according to claim 1. A current detector for detecting a current flowing from the DC power source to the inverter;
Detecting the predetermined section based on a detection result by the current detection unit;
The inverter control device according to claim 2. The predetermined section is set as a section having an electrical angle of 60 degrees centered on the maximum current value or the minimum current.
The inverter control apparatus in any one of Claims 1-3.   The inverter control device according to claim 1, wherein the predetermined value is either a minimum output voltage or a maximum output voltage of the inverter.   A compressor provided with the inverter control apparatus in any one of Claims 1-5.

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