JP2010045884A - Motor driving device and current detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor driving device, which carries out current control with reduced oscillation in PI computation output using a current detection value based on a moving average of more than one uptake current per carrier frequency using a predicted current and a measured current, and with reduced oscillation in the actual current of a motor, and to provide a current detection method, which reduces a computation error in a current detection value based on a moving average of more than one uptake current per carrier frequency using a predicted current and a measured current and carry out delay time compensation. <P>SOLUTION: In the motor driving device, with respect to a proportional of a current controller 1, predicted currents obtained at three current uptake points and detected currents obtained at five current uptake points are integrated at integrators 11, 12, added at an adder 14, and divided at a divider 16 to determine a moving average value and this is taken as a current detection value. With respect to an integral term of the current controller, detected currents obtained at five current uptake points and detected currents obtained at three current uptake points are integrated at integrators 12, 13, added at an adder 15, and divided at divider 17 to obtain a moving average value and this is taken as an current detection value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a motor drive device that performs current control by proportional integral calculation (hereinafter referred to as PI calculation) of a current detection value using a predicted current and a detected current, and captures and captures the predicted current and detected current multiple times per carrier cycle. The present invention relates to a current detection method for obtaining a current detection value by moving average of currents.

  As shown in FIG. 2, a control circuit for a motor drive device using an inverter generally includes a current controller 1, a PWM carrier signal generator 2, a comparator 3, an inverter main circuit 4, a current detector 5, and an A / D converter. 6 and drives a motor (AC motor) 7. As shown in FIG. 3, the current controller 1 calculates a deviation between the current command value and the current detection value, and generates a voltage command value (PI calculation output) such that the deviation is reduced by the PI calculation.

  FIG. 2 shows a circuit having the most general configuration as a current detection method for a motor drive device. This circuit uses an A / D conversion trigger signal synchronized with a carrier signal for generating a PWM signal of an inverter, and has a one-carrier cycle. This is a method of taking the detected current output from the current detector 5 into the A / D converter 6 only once or twice. Although this method is simple, there is a problem that it is vulnerable to current ripple components caused by PWM voltage pulses and noise.

As a current detection method for improving the problems caused by the current detection method of FIG. 3, there is a multipoint synchronous current detection method shown in FIG. This is a technique in which a plurality of currents are taken into a control circuit per carrier cycle, and the obtained current is subjected to moving average to obtain a current detection value (see, for example, Patent Document 1). In FIG. 4, eight currents i _{(n) to} i _(n-7) per one carrier cycle are taken into the A / D converter 6 from the current detector 5 and the taken eight currents i _{(n) to} i are taken. _(n-7) is shifted by the shift register 8, and the current detection values (i _{(n) to} i _(n-7) ) at the eight points are integrated by the integrator 9 and 1/8 by the divider 10. A moving average is obtained by dividing. Although this method can greatly reduce the influence of the current ripple component and noise caused by the PWM voltage pulse, since it takes a moving average, the obtained current detection value has a time delay corresponding to approximately a half cycle of the carrier.
JP 2003-219690 A

  In order to suppress the time delay of the current detection value, when a multipoint synchronous current detection circuit (for example, current acquisition of 8 points per carrier cycle) that compensates the time delay by the current detection value by the predicted current and the detection current is used The current controller is as shown in FIG. The predicted current value of 3 points and the detected current value of 5 points are integrated by the integrator 9, and a current detection value is obtained by dividing by 1/8 by the divider 10, and the deviation between this and the current command value is calculated. It is input to the current controller. The current detection value is less affected by the current ripple component and noise caused by the PWM voltage pulse, and the time delay is reduced.

  However, a calculation error is included in the component due to the predicted current in the current detection value. In other words, for the calculation of the predicted current, when the future motor voltage command used for calculating the predicted PWM pulse is used, it is necessary to configure the feedback control of the motor constant, current and voltage. Since the meaning of performing feedforward current prediction with a low load is lost, the current one is used, and an error occurs in the calculation of the predicted current in the control state where the voltage command value is changing.

The calculation for obtaining the predicted current i from the motor voltage command assumes that the voltage drop due to the winding resistance of the motor is small, and uses only the voltage v applied to the motor and the inductance L of the winding as parameters, i = (1 / L) ∫ (v) dt. Here, assuming that the induced electromotive force e ₀ is constant during the control cycle among the elements constituting the voltage v, the change in the predicted current i is determined by the voltage obtained by subtracting the induced electromotive force e ₀ from the voltage v. The predicted current i that changes by the control cycle does not include errors between the design value and the measured value of the inductance L of the motor winding, magnetic saturation and temperature errors, and various other factors such as winding resistance and other wiring. Since the parameter is ignored, an error occurs between the calculation and the actual measurement.

Further, the induced electromotive force e ₀ subtracted from the voltage v in order to obtain the current change component is obtained from the multiplication of the magnetic flux φ and the angular velocity ω of the permanent magnet, and it is considered that an error also occurs here.

  When a current detection value with these calculation errors is input to the current controller, the current detection value becomes "actual current value ± calculation error", and "deviation between current command and actual current value" and "current command and calculation error" When the current deviation between the current command value and the current detection value by the moving average is small compared to the magnitude of the calculation error of the current detection value, the component of the deviation due to the calculation error is proportional. Both the term and the integral term become prominent, the integration error of the integrator is large, the steady state deviation cannot be canceled well by the integrator, and control is performed with the output current and the actual current including a large amount of error. It becomes unstable, such as oscillating due to changes in value.

  From the above, the object of the present invention is to use the current detection value based on the moving average of a plurality of captured currents per carrier cycle using the predicted current and the detected current, and thereby the vibration of the PI calculation output and the actual current of the motor. Motor drive device capable of current control with reduced vibration and current capable of reducing calculation error of current detection value and compensating for delay time by moving average of captured current multiple times per carrier cycle using predicted current and detection current It is to provide a detection method.

  According to the present invention, in a device or method for performing current control of an object to be controlled by PI calculation of a deviation between a current command value and a current detection value by a current controller, the proportional term of the current controller compensates for a delay due to a predicted current and a detected current. The motor drive device is capable of current control with reduced PI calculation output vibration and motor actual current vibration by using the detected current as the integral term of the current controller and detecting the delay only with the detected current. And a current detection method that reduces a calculation error of a current detection value by a moving average of a plurality of currents taken per carrier cycle using a predicted current and a detection current and compensates for a delay time. Features.

(1) The current to be controlled is captured multiple times per carrier cycle, the current detection value is obtained by moving average of the captured current, and the deviation between the current detection value and the current command value is proportional to the current controller. In the motor drive device that performs integral calculation and performs current control of the control target,
The proportional term of the current controller is provided with calculation means for obtaining the current detection value by a moving average of a predicted current at a plurality of sampling points and a detection current at a plurality of sampling points,
The integral term of the current controller includes a calculation means for obtaining the detected current value by a moving average of detected currents at a plurality of sampling points.

(2) Proportional integral calculation is performed on the deviation between the detected current value and the current command value by the current controller to control the current to be controlled, and the current to be controlled is fetched multiple times per carrier cycle. A current detection method for obtaining the current detection value by moving average,
The proportional term of the current controller obtains the current detection value by a moving average of a predicted current at a plurality of sampling points and a detection current at a plurality of sampling points,
The integral term of the current controller obtains the detected current value by a moving average of detected currents at a plurality of sampling points.

  As described above, according to the present invention, among the current controllers that perform PI (proportional integration) calculation from the deviation between the current command value and the current detection value, the current detection value input to the proportional term is delayed by the predicted current and the detection current. In order to obtain a compensated current control output, and to obtain a current control output in which the calculation error is reduced by using only the detected current as the current detection value input to the integral term, the vibration of the PI calculation output and the vibration of the actual motor current are reduced. Current control is possible. In addition, the calculation error of the current detection value can be reduced and the delay time can be compensated by the moving average of the current taken a plurality of times per carrier cycle.

  FIG. 1 is a configuration diagram of a current controller showing an embodiment of the present invention. In the present embodiment, in a motor drive device that performs current control with a current controller that obtains a current detection value by a multipoint current detection circuit, the current detection value input to the proportional term takes a plurality of currents per carrier cycle, The current that is compensated for the delay due to the predicted current and the detected current at this capture point (hereinafter referred to as multiple sampling points) and the current detection value that is input to the integral term are those that are not compensated for the delay due to the detected current at multiple sampling points. .

The multi-point current detection circuit is a current that generates a current deviation that is input to the proportional term by holding three points of detected current in addition to the predicted current of three points and the five points of detected current. The detected values include three predicted currents i _{(n + 1) to} i _{(n + 3)} and five detected currents i _{(n-4) to} i _(n) . Is used. A moving average of eight detection currents i _{(n-7) to} i _(n) is used as a current detection value for generating a current deviation input to the integral term.

The calculation elements of these moving averages are an accumulator 11 for accumulating _three predicted currents i _{(n + 1) to} i _{(n + 3)} and five detected currents i _{(n-4) to} i _{(n )} Integrating unit 12, integrating three detection currents i _{(n-7) to} i _(n-5) , and adding unit adding the integration results of integrating units 11 and 12 14, an addition unit 15 that adds the integration results of the integration units 12 and 13, a division unit 16 that performs division of 1/8 of the addition result of the addition unit 14 and inputs the current detection value to the proportional term, The dividing unit 17 is configured to divide 1/8 of the addition result of the adding unit 15 and input the detected current value to the integral term.

  With this configuration, a current detection value that has a time delay but no calculation error is input to the integral term, and the output of the integral term is not affected by the calculation error. Originally, the output of the integral term is time-delayed, and when the current deviation is large, the output of the proportional term is large when the current deviation is large. Is hardly reflected in the output.

  Here, when it is close to the steady state, that is, when the current deviation is small, a component due to calculation error appears in both the proportional term and the integral term, and the voltage command value and the actual current value oscillate in the conventional current detection circuit configuration. , Will not converge, will affect. This effect is particularly noticeable when the gain of the current controller is high.

  On the other hand, in the present embodiment, when the steady state is close, that is, when the steady deviation is small, the output command for reducing the steady deviation becomes proportionally small as the steady deviation becomes small with only the proportional term. Cannot be set to "0". In order to bring this deviation closer to “0”, an output command is obtained by integrating the steady deviation with the integral term.

  That is, in this embodiment, since the proportional term requires responsiveness, the detection delay deteriorates the responsiveness. Therefore, a deviation that compensates for the delay is input to the proportional term, and the integral term requires high-speed responsiveness. Since there is no delay in the integral term, a deviation with no calculation error is input.

  Note that the current controller according to the present embodiment is not limited to the current control of an electric motor, and the method and apparatus for current detection by a multipoint synchronous current detection circuit that performs delay time compensation by a predicted current are generally applied. Thus, an equivalent effect can be obtained.

The block diagram of the current controller which shows embodiment of this invention. Outline of configuration of motor driving device. Outline of configuration of current controller. The structural example of a multipoint synchronous current detection circuit. The block diagram of the conventional current controller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current controller 7 Motor 9 Accumulator 10 Divider 11, 12, 13 Accumulator 14, 15 Adder 16, 17 Divider

Claims (2)

The current to be controlled is captured multiple times per carrier cycle, the current detection value is obtained by moving average of the captured current, and the deviation between the current detection value and the current command value is proportionally integrated with the current controller. In the motor drive device that performs current control of the controlled object,
The proportional term of the current controller is provided with calculation means for obtaining the current detection value by a moving average of a predicted current at a plurality of sampling points and a detection current at a plurality of sampling points,
The motor drive device according to claim 1, wherein the integral term of the current controller includes a calculation means for obtaining the current detection value by a moving average of detection currents at a plurality of sampling points. The current control value is controlled by proportional-integral calculation of the deviation between the detected current value and the current command value, and the current to be controlled is captured multiple times per carrier cycle. A current detection method for obtaining the current detection value by
The proportional term of the current controller obtains the current detection value by a moving average of a predicted current at a plurality of sampling points and a detection current at a plurality of sampling points,
An integral term of the current controller obtains the detected current value by a moving average of detected currents at a plurality of sampling points.

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