JP2010288370A - Controller for inverter and method for controlling inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller for an inverter reducing a ripple. <P>SOLUTION: The controller 300 includes an f-V converter 302, a voltage limiter 304, an electrical-angle computing element 306, a sine-wave data table 308, a three-phase sine-wave voltage computer 310, a low-pass filter 312, a PWM preparation part 314, and a memory 318. The memory 318 stores a frequency preset as a frequency easily causing a DC power supply to the inverter 350 to pulsate with respect to the frequency of the object to be driven (such as a compressor) of an AC motor 360. The voltage limiter 304 corrects a voltage command value for controlling the inverter 350 to be a value smaller than the voltage command value computed on the basis of the frequency imparted as a command when the frequency imparted as the command to the object to be driven is close to the preset frequency and the modulation rate of the inverter 350 is close to an output limit. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to control of an inverter, and more particularly to control of a voltage type PWM (Pulse Width Modulation) inverter.

  In a compressor or the like mounted on a product such as an air conditioner or a refrigerator, a motor including a rotor and a stator coil is used. The motor is driven by supplying a phase current controlled by a motor driving device to the stator coil. At this time, the system for controlling the driving of the motor includes a phase current detector, a pulse modulation (PWM) generator, a triangular wave generator, and the like. Then, a pulse width modulation signal that changes in a three-phase sine wave shape including a U phase, a V phase, and a W phase is generated in correspondence with the position of the rotor, and is output to the drive circuit.

  The drive circuit outputs a transistor drive signal to the inverter circuit in correspondence with the pulse width modulation signal, and turns on or off the six transistors in the inverter. As a result, a three-phase current is generated, and current is supplied to the stator coil.

  Generally, in an inverter, three pairs of transistors in which upper and lower transistors are connected in series are arranged in order to generate a three-phase current. By turning on the upper transistor and turning off the lower transistor, a positive polarity DC (Direct Current) voltage can be supplied to each stator terminal. Conversely, the upper transistor is turned off and the lower transistor is turned off. By turning on the transistor, a voltage of 0 V (GND potential) can be supplied to each stator terminal.

  In the above case, in order to determine the modulation rate, generally, for example, fV constant control is used, and the voltage to be applied is determined by the frequency. Then, for each period of the modulation pulse, a value obtained by dividing the magnitude of the DC (Direct Current) power supply with respect to the command voltage value is output as the ON width DUTY ratio of the pulse.

  It is known that a beat phenomenon in which a phase current pulsates with respect to a ripple of a DC power supply occurs. Due to the influence of the beat phenomenon, the motor may not be able to operate due to the current jumping up or out of step.

  FIG. 1 shows the PWM pulse OnDuty and actual output voltage waveforms during constant phase voltage control when there is a ripple of the DC power supply. In the case of an average DC voltage value of 280 V, a ripple amplitude of 70 V, and a phase voltage effective value command of 50 V, the average modulation rate is about 50%. At this level, when the DC voltage suddenly increases due to the ripple of the DC power supply, the duty is decreased by that amount, and conversely, when the DC voltage decreases, the duty is increased by that amount. A sinusoidal wave can be obtained, and it can be seen that the influence of the ripple of the DC power supply is absorbed.

  FIG. 2 is a diagram showing a PWM pulse OnDuty and an actual output voltage waveform (when the average modulation rate is about 100%) during constant phase voltage control when there is a DC power supply ripple. As shown in FIG. 2, even if the conditions of the DC power source are the same, when the phase voltage effective value command is 100 V, the average modulation rate is almost 100%, and when the DC voltage decreases, an attempt is made to increase the duty accordingly. However, Duty cannot output more than 100%. Therefore, it can be seen that an ideal sine wave cannot be maintained for the output voltage, and the influence of the ripple of the DC power supply cannot be absorbed.

  In order to reduce this, it is necessary to reduce the ripple of the DC power supply. In order to realize this, the capacity of the smoothing capacitor of the DC smoothing circuit is increased, or a large reactor is inserted into the DC line. There is a need. However, if it does in this way, there will be a problem that an apparatus will enlarge and cost will rise.

  Therefore, as a method for reducing this by control, for example, Japanese Patent Application Laid-Open No. 2004-104898 (Patent Document 1) detects the pulsating phase current, calculates its compensation voltage component, and negatively affects the voltage command value to be applied. A technique for reducing ripples by feedback is disclosed. Japanese Patent Laying-Open No. 2006-115576 (Patent Document 2) discloses a method for detecting a pulsation component from a pulsation of a direct current and correcting the frequency of the motor based on the pulsation component.

JP 2004-104898 A JP 2006-115576 A

  As in the technique disclosed in Patent Document 1 or 2, an expensive current sensor is required to detect the pulsation component of the phase current, or a high-speed A / D ( There is a problem that a CPU (Central Processing Unit) or other processor having an analog to digital conversion function is required.

  In a region where the modulation factor is already at the output limit (for example, a region in which a proportional relationship (linearity) cannot be ensured with characteristics between the input modulation factor and the output voltage, a saturation region, etc.) There may be a case where the compensation voltage cannot be applied as in the method described.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an inverter control device in which ripple is reduced without increasing cost. Another object is to provide a control device in which ripple is reduced without being restricted by the output limit of the modulation rate.

  Another object is to provide a method for controlling an inverter such that ripple is reduced without increasing cost. Another object is to provide a method for controlling the inverter so that the ripple is reduced without being constrained by the output limit of the modulation rate.

  According to one embodiment, a control device for an inverter connected to a synchronous motor is provided. This control device includes a storage device that stores a preset frequency as a frequency at which a DC power source is likely to pulsate among frequencies to be driven by a synchronous motor, and a frequency that is given as a command to the drive target in the vicinity of the preset frequency. When the inverter modulation rate is near the output limit, the voltage command value used for inverter control is set to a value smaller than the voltage command value calculated based on the frequency given as the command. Correction means for correcting.

  Preferably, the correction means is configured to calculate a voltage command value that is determined in advance according to the drive target in order to absorb fluctuations in the direct current.

  Preferably, the inverter is connected to the converter. The converter includes a DC smoothing circuit. The DC smoothing circuit includes a capacitor. The correction means is configured to change the correction amount of the modulation factor according to the capacitance of the capacitor.

  Preferably, the inverter is connected to the converter. The converter includes a reactor. The correction means is configured to change the correction amount of the modulation factor according to the capacity of the reactor.

  Preferably, the control device for the inverter further includes smoothing means for adjusting the correction amount so that the modulation rate converges to a predetermined value as the frequency given as a command to the drive target approaches a preset frequency.

  According to another embodiment, a method for controlling an inverter connected to a synchronous motor is provided. This method includes a step of loading a frequency set in advance as a frequency at which the DC power source is likely to pulsate among frequencies to be driven by the synchronous motor, and a frequency given as a command to the drive target is in the vicinity of the preset frequency. When the inverter modulation rate is close to the output limit, the voltage command value used for inverter control is corrected to a value smaller than the voltage command value calculated based on the frequency given as the command. Steps.

  According to the control device according to an embodiment, the ripple is reduced without increasing the cost. Further, according to another embodiment, the ripple is reduced without being restricted by the output limit of the modulation rate.

  The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention taken in conjunction with the accompanying drawings.

It is a figure showing PWM pulse OnDuty at the time of phase voltage constant control in the case where there is a DC power supply ripple, and an actual output voltage waveform (in the case of an average modulation rate of about 50%). It is a figure showing PWM pulse OnDuty at the time of phase voltage constant control in case there is DC power supply ripple, and an actual output voltage waveform (in the case of an average modulation rate of about 100%). It is a figure showing the structure of the control apparatus 300 which concerns on one Embodiment. It is a figure showing the control apparatus 400 which concerns on the modification of this one Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  FIG. 3 is a diagram illustrating a configuration of control device 300 according to the present embodiment. The control device 300 controls, for example, a three-phase AC motor 360 that drives an air conditioner, a refrigerator, a freezer, and other devices. In the present embodiment, the drive target of AC motor 360 is a compressor, for example, but the drive target is not limited to the compressor.

  The control device 300 is realized as a microcomputer, for example. In this case, the arithmetic processing and the correction processing executed by the control device 300 are realized as each processing step by the microcomputer executing instructions. In another aspect, the control device 300 can also be realized as a wire-connected device such as a combination of circuit elements that realize each process.

  The control device 300 is electrically connected to the inverter 350. A converter circuit 330, a DC voltage detection unit 340, and an AC motor 360 are electrically connected to the inverter 350. Converter circuit 330 is connected to AC power supply 320. Converter circuit 330 includes a DC smoothing circuit 332 and a reactor 334.

  The control device 300 includes an fV conversion unit 302, a voltage limiter 304, an electrical angle calculator 306, a sine wave data table 308, a three-phase sine wave voltage calculation unit 310, a low-pass filter 312, and a PWM generator. A unit 314 and a memory 318. The control device 300 is realized as a microcomputer, for example. In this case, the microcomputer functions as the control device 300 by executing a program for executing processing of each unit constituting the control device 300.

  In one aspect, the memory 318 stores a frequency set in advance as a frequency at which the DC power supply to the inverter 350 is likely to pulsate among the frequencies of the drive target (for example, the compressor) of the AC motor 360. The voltage limiter 304 is used for controlling the inverter 350 when the frequency given as a command for the drive target is in the vicinity of a preset frequency and the modulation rate of the inverter 350 is in the vicinity of the output limit. The voltage command value to be corrected is corrected to a value smaller than the voltage command value calculated based on the frequency given as the command. Here, the vicinity of the preset frequency is a value in a certain range including the value of the frequency, for example, and is defined as, for example, several percent before and after the frequency. The vicinity of the output limit is not limited to the upper limit value itself, but is defined as a value that is several percent smaller than the upper limit value.

  In another aspect, the voltage limiter 304 is configured to calculate a voltage command value that is predetermined according to the drive target in order to absorb the fluctuation of the direct current. In another aspect, the voltage limiter 304 may be configured to change the correction amount of the modulation factor according to the capacitance of a capacitor (not shown) included in the DC smoothing circuit 332. In another aspect, the voltage limiter 304 may be configured to adjust the correction amount of the modulation factor according to the capacity of the reactor 334.

  More specifically, AC power supply 320 is supplied from an outlet provided on a power line laid in a house, for example. Converter circuit 330 converts alternating current from alternating current power supply 320 into direct current, and supplies it to inverter 350. DC voltage detector 340 detects the voltage value of the current output from converter circuit 330. For example, the DC voltage detection unit 340 detects the DC voltage value Vdc based on the A / D function of a microcomputer for each PWM control cycle. The inverter 350 converts direct current into alternating current.

  The sine wave data table 308 stores one or more sine wave data prepared in advance. The sine wave table 308 is realized as, for example, a nonvolatile memory included in a microcomputer that implements the control device 300. In another aspect, the sine wave data may be calculated by calculation instead of a mode in which the sine wave table 308 holds the sine wave data in advance.

  When the frequency command value ω * is input to the control device 300, the fV conversion unit 302 calculates a command value V * of a voltage effective value proportional to the frequency. The electrical angle calculation unit 306 integrates the frequency command value ω * to calculate the electrical angle θ.

  The low pass filter 312 calculates a DC voltage value (Vdc_lowpass) obtained by cutting the high frequency band based on the voltage value detected by the DC voltage detection unit 340 so as not to be affected by the beat phenomenon. The output of the low pass filter 312 is input to the voltage limiter 304.

  The frequency command value ω * is also input to the voltage limiter 304. The voltage limiter 304 calculates the modulation rate Mrate using the following calculation formula.

  The modulation rate Mrate is equal to or higher than a preset threshold Mrate_th (as an example of this embodiment, suppose that 90%, that is, the modulation amount correction amount is 10%), and the frequency at which the DC power source is likely to pulsate. When the frequency fb is preset and stored (not limited to the value fb but may have a certain range of frequencies), the voltage limiter 304 is a command derived by the fV conversion unit 302. The value V * is corrected using the following formula:

  The voltage effective value correction value V * corrected by the voltage limiter 304 is input to the three-phase sine wave voltage calculation unit 310. The three-phase sine wave voltage calculator 310 calculates the voltage effective value command value V * corrected by the voltage limiter 304, the sine wave data held in the sine wave table data 308, and the electrical angle calculation for each PWM cycle. The voltage command values Vu, Vv, and Vw * for the U, V, and W phases are calculated by the following formula using the electrical angle θ calculated by the device 306.

  The calculation result of the three-phase sine wave voltage calculation unit 310 is input to the PWM creation unit 314. The PWM creation unit 314 calculates the ON pulse widths OnDutyU, OnDutyV, OnDutyW of the U, V, and W phases based on the phase voltage command values Vu, Vv, Vw, and the DC voltage value Vdc using the following equations. .

Each calculated value is input to the inverter 350 as a PWM signal. Inverter 350 drives AC motor 360 based on each signal.

  FIG. 4 is a diagram illustrating a control device 400 according to a modification of the present embodiment. The control device 400 according to the present modification has a smoothing function that adjusts the correction amount so that the modulation rate converges to a predetermined value as the frequency given as a command to the drive target approaches a preset frequency. It is different.

  That is, in the control device 400 according to this modification, the voltage limiter 304 includes the smoothing circuit 410. The smoothing circuit 410 adjusts the correction amount so that the modulation rate converges to a predetermined value as the frequency ω * given as a command to the drive target approaches the preset frequency. For example, the convergence mode is stored in advance in the memory 318 as map information so that the modulation rate changes according to a constant change rate. The default value is also stored in the memory 318 in advance. In another aspect, instead of the map information, the voltage limiter 304 may perform calculation using a function prepared in advance for convergence. According to the configuration according to the present modification, the correction value is adjusted smoothly, so that prevention of phase current pulsation can be realized smoothly.

  As described above, according to the control device 300 according to the embodiment of the present invention or the control device 400 according to the modification, the frequency that is likely to occur empirically is related to the phase current pulsation (beat phenomenon) due to the ripple of the DC voltage. Stored in the memory 318 in advance. Then, the voltage limiter 304 refers to the frequency stored in the memory 318 and deliberately lowers the command voltage value in the vicinity of the overmodulation region where it is difficult to absorb the influence of the DC voltage ripple. To correct. In this way, pulsation of the phase current can be prevented without using an expensive current sensor. As a result, it is possible to control the driving of the AC motor 360 while suppressing an increase in cost and without complicating the control and further suppressing a decrease in efficiency due to a low voltage output.

  The embodiment disclosed this time should 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.

  300 controller, 302 f-V conversion unit, 304 voltage limiter, 306 electrical angle calculator, 308 sine wave data table, 310 three-phase sine wave voltage calculation unit, 312 low-pass filter, 314 PWM creation unit, 318 memory, 320 AC power supply, 330 converter circuit, 332 DC smoothing circuit, 334 reactor, 340 DC voltage detection unit, 350 inverter, 360 AC motor, 400 controller, 410 smoothing circuit.

Claims (6)

A control device for an inverter connected to a synchronous motor,
A storage device for storing a frequency set in advance as a frequency at which the DC power source is likely to pulsate among the frequencies to be driven of the synchronous motor;
When a frequency given as a command for the drive target is in the vicinity of the preset frequency and the modulation rate of the inverter is in the vicinity of an output limit, a voltage command value used for controlling the inverter is And a correction means for correcting the value to a value smaller than a voltage command value calculated based on the frequency given as the command.   The inverter control device according to claim 1, wherein the correction unit is configured to calculate a voltage command value determined in advance according to the drive target in order to absorb the fluctuation of the direct current. The inverter is connected to a converter, the converter includes a DC smoothing circuit, the DC smoothing circuit includes a capacitor,
The inverter control device according to claim 1, wherein the correction unit is configured to change a correction amount of the modulation factor according to a capacitance of the capacitor. The inverter is connected to a converter, the converter including a reactor;
The inverter control device according to claim 1, wherein the correction unit is configured to change a correction amount of the modulation factor according to a capacity of the reactor.   5. The smoothing device according to claim 1, further comprising a smoothing unit that adjusts the correction amount so that the modulation factor converges to a predetermined value as the frequency given as a command to the drive target approaches the preset frequency. The control apparatus of the inverter in any one of. A method for controlling an inverter connected to a synchronous motor,
Loading a frequency set in advance as a frequency at which the DC power source is likely to pulsate among the frequencies to be driven of the synchronous motor;
When a frequency given as a command for the drive target is in the vicinity of the preset frequency and the modulation rate of the inverter is in the vicinity of an output limit, a voltage command value used for controlling the inverter is And a step of correcting to a value smaller than a voltage command value calculated based on a frequency given as the command.

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