JP2010252595A - Motor drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor drive which reduces the influence of switching noises and current ripples by a power element and improves a current control response. <P>SOLUTION: The motor drive includes a carrier signal generator 1 which outputs a triangular wave carrier signal 11, a current detection timing generator 2 which outputs a current detection trigger 12 based on the carrier signal 11 as a reference signal, a motor current detector 3 which detects an average current value in a fixed section, a current controller 4 which carries out current control to cause the average current detected by the motor current detector 3 to follow a current instruction and updates a voltage instruction at crest and trough of the carrier signal 11, and a PWM controller 5 which inputs the carrier signal 11 and the voltage instruction and outputs a PWM signal to an inverter unit. The motor drive matches a period of crest and trough of the carrier signal 11 to a fixed section for detection of the average current value in terms of time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for suppressing vibrations by optimizing current detection timing in current feedback control.

  Current control using a motor drive device has generally been performed since the era of analog circuits for high-speed, high-response control of servo motors. In recent years, advances in microcomputer and LSI technology have led to digitalization of current control, and analog control has made it possible to perform complex control that was difficult to achieve in terms of design and cost. Contributes greatly to high functionality.

  In general, in current control, a three-phase voltage command value is generated so that a three-phase current of a motor is detected and followed by the current command value, and output to a power amplifier composed of a plurality of semiconductor switches. A desired three-phase AC voltage is applied to the motor by a combination of ON / OFF of a plurality of semiconductor switches.

  PWM control, which generates a three-phase AC voltage from a DC voltage using a plurality of semiconductor switches, outputs an ON / OFF signal for the semiconductor switch according to the carrier frequency and the voltage command value, and a pulse voltage between the motor lines. Is applied.

  The effective voltage value applied to the motor can be made sinusoidal by controlling the width of the pulse by ON / OFF of the switch. Although the finer control can be performed as the carrier frequency becomes higher, there are problems such as switching loss and heat generation, and the frequency is generally several kHz to several tens kHz.

  The current control using the PWM method has a problem that switching noise of the semiconductor switch is superimposed on the current and adversely affects the current control. Further, since a pulsed voltage is applied between the motor wires, current ripple occurs unless the carrier frequency is sufficiently high with respect to the electrical time constant of the motor. Actually, the carrier frequency cannot be increased indefinitely due to the above-described problems such as loss and heat generation, so that a certain amount of current ripple occurs.

  In order to avoid the effects of switching noise, current detection is performed at the peak and valley portions of the carrier signal that are not switched except when the maximum torque is applied to the motor, so that accurate current can be obtained particularly in the normal operating region. A method for obtaining a value has been proposed (see, for example, Patent Document 1).

JP 11-136950 A

  However, the above-described technique has a problem that the influence of the current ripple due to the relationship between the electric time constant of the motor and the carrier frequency cannot be avoided. In particular, in the case of a current detection method that detects an average value of current values in a certain section, the average current value in a certain section from the peak / valley of the carrier is detected. It becomes a factor of vibration.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a motor drive device that can reduce the influence of current ripple and suppress the occurrence of vibration.

  The motor drive device according to claim 1 is a motor drive device having a current feedback control by PWM control using a current detector for detecting a motor current, a carrier signal generator for outputting a triangular wave carrier signal, and a predetermined section A motor current detector that detects an average current value of the current, a current detection timing generator that outputs a current detection trigger based on the carrier signal, and a current command value that follows the average current value detected by the motor current detector A current controller that performs current control so that the voltage command value is updated at the peaks and valleys of the carrier signal, and a PWM controller that inputs the carrier signal and the voltage command value and outputs a PWM signal to the inverter unit. The period of the peaks and valleys of the carrier signal is made to coincide with the time of a certain interval for detecting the average current value.

  The motor driving apparatus according to claim 2 performs current control between detection of the average current value.

  Furthermore, the motor drive apparatus according to claim 3 uses a ΣΔ type current detector.

  According to the motor drive device of the first aspect, since the average current value detected by the motor current detector is close to the average current value between the peaks and valleys of the carrier signal, the influence of the current ripple can be reduced and the occurrence of vibration can be reduced. Can be suppressed.

  Further, according to the motor drive device of the second aspect, the delay time from the current detection to the update of the voltage command value can be minimized, and the responsiveness is improved.

  Furthermore, according to the motor drive device of the third aspect, the current detection section can be arbitrarily changed by decimation setting, and setting suitable for the carrier cycle becomes possible.

1 is a block diagram of the main part of a motor drive device according to a first embodiment of the present invention. Timing chart of carrier signal and current detection and current control in Embodiment 1 of the present invention Explanatory drawing of the switching waveform and current ripple waveform in Example 1 of this invention

Example 1
Embodiment 1 of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram of a main part of a motor driving device, a carrier signal generator 1 that outputs a carrier signal 11, a current detection timing generator 2 that outputs a current detection trigger signal 12 from the carrier signal 11, and a current detection. A motor current detector 3 that outputs a current detection value 13 when the trigger signal 12 is input, a current controller 4 that outputs a voltage command 14 from the current detection value 13, and a PWM output 15 from the voltage command 14 and the carrier signal 11 The PWM controller 5 which produces | generates is provided.

First, the current detection timing will be described. FIG. 2 shows a timing diagram. The detection interval of the motor current detector 3 is set in advance to be the same as the peak / valley period of the carrier signal. For example, when the motor current detector 3 is of the ΣΔ method, the detection section can be set by setting decimation.

  The current detection trigger signal 12 is set to be ahead of the peak and valley of the carrier signal 11 by the processing time of the current controller. The current detection value is latched by the current detection trigger signal 12, and simultaneously the current control is started, so that the detected current value can be immediately reflected in the current control.

  Furthermore, since the carrier signal 11 has peaks and valleys after the current control is completed, the update to the voltage command 14 is also minimized, and the update delay from the motor current detection to the voltage command can be minimized. When the motor current detector 3 is of the ΣΔ system, normal current detection is always performed, and when the current detection trigger 12 is input, the average current value from that point to the previous section set by decimation is detected. can do. The decimation setting can be easily changed by parameter setting without changing the hardware.

  Next, the reason why the influence of the current lip can be reduced by matching the period of the peaks and valleys of the carrier signal 11 with the detection interval of the motor current detector 3 will be described.

  FIG. 3 shows the switching waveform and current ripple caused by the PWM signal. As shown in FIG. 3, the current value varies between peaks and valleys of the carrier signal 11. For example, when the current detection period is shorter than the period of the peaks and valleys of the carrier signal 11, the current detection value varies greatly depending on the detection timing. This fluctuation causes vibration of the motor.

  According to the present invention, since the period of the peaks and valleys of the carrier signal 11 and the detection interval of the motor current detector 3 are the same, the current ripple is averaged regardless of the timing, and the influence can be almost eliminated. it can.

  Furthermore, if the normal current detection interval is lengthened, the current detection resolution can be increased, but the conventional current detection interval can only be increased to about ¼ of the period of the peaks and valleys of the carrier signal due to the problem of responsiveness and current ripple. The current detection resolution could not be increased. According to the present invention, since the current detection section can be extended to the period of the peaks and valleys of the carrier signal, there is also an effect that the current detection resolution can be increased.

  It should be noted that it is best if the period of the peaks and valleys of the carrier signal and the detection interval of the current detector can be completely matched, but even if it cannot, the effect of the present invention can be obtained by bringing them as close as possible.

  The motor drive device of the present invention is also useful for applications that require high-speed response and control stability.

DESCRIPTION OF SYMBOLS 1 Carrier signal generator 2 Current detection timing generator 3 Motor current detector 4 Current controller 5 PWM controller 11 Carrier signal 12 Current detection trigger signal 13 Current detection value 14 Voltage command 15 PWM output

Claims (3)

In a motor drive device having a current feedback control by PWM control using a current detector for detecting a motor current,
A carrier signal generator for outputting a triangular wave carrier signal;
A motor current detector for detecting an average current value in a certain section;
A current detection timing generator that outputs a current detection trigger based on the carrier signal;
A current controller that performs current control so that the average current value detected by the motor current detector follows the current command value, and updates the voltage command value in the peaks and valleys of the carrier signal;
A PWM controller that inputs the carrier signal and the voltage command value and outputs a PWM signal to the inverter unit,
A motor driving device characterized in that a period of peaks and valleys of the carrier signal coincides with a time of a certain section for detecting the average current value.   The motor drive device according to claim 1, wherein the current controller performs current control between a completion of a certain period of detecting an average current value and a peak and valley of a carrier.   The motor driving device according to claim 1, wherein a ΣΔ type current detector is used.

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