JPH0715972A - Inverter controller - Google Patents

Abstract

PURPOSE:To reduce the ripple torque of a motor by eliminating circuit components causing gain error and offset during measurements of output current in an inverter controller. CONSTITUTION:A sigma delta converter 30 for converting the potential difference of a current detection resistor 16 to a Sigma-Delta-modulated digital signal, a photocoupler 25 for transferring the digital signal after electrically insulating it, and a digital filter 32 for demodulating the digital signal after transfer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control device for driving a motor by detecting a phase current of the motor and performing feedback control.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of a circuit of a motor drive inverter control device using a conventional technique. The three-phase AC power is converted into a DC voltage of an appropriate voltage by the converter 1, and then two sets of two connected in series are connected in parallel by three power elements 2, 3, 4, 5, 6, and 7,
The DC power is converted into AC power for driving the motor. Gate circuits 8, 9, 10, 11, 12, and 13 are connected to the power elements 2, 3, 4, 5, 6, and 7, respectively. The gate circuits 8, 9, 10, 11, 12, 13 are PW
It is controlled by the M signal generation circuit 14. Current detection resistors 16 and 17 are inserted in series in the output circuit of the inverter to which the motor 15 is connected. An insulation amplifier 18 and an A / D converter 19 are connected to both ends of the current detection resistor 16. Similarly, an insulation amplifier 20 and an A / D converter 21 are connected to both ends of the current detection resistor 17. The phase currents Iu and Iv of the motor 15 are taken out as voltage drops Vsu and Vsv of the current detection resistors 16 and 17 inserted in series with the output of the inverter, and input to the isolation amplifiers 18 and 20, respectively. The isolation amplifiers 18 and 20 transmit the input signals while electrically insulating them, and output analog signals SigAu and SigAv having the same potential as the current control circuit 22. The analog signals SigAu and SigAv are A / D converter 1
It is converted into a digital value by 9 and 21 and input to the current control circuit 22. The current control circuit 22 obtains the current deviation of each phase from the current commands Iu *, Iv * input from the higher-order control circuit and the detected phase currents Iu, Iv, and proportionally and integrally amplifies the current deviation for each motor to obtain each motor. It outputs voltage commands Vu *, Vv *, Vw * to be applied to the phases. Voltage command V
u *, Vv *, and Vw * are PWM signals having an on / off duty proportional to the command value, generated by the PWM signal generation circuit 14.
The signal is converted into a signal, and a dead time for preventing an arm short circuit is added, and the signal becomes an on / off command signal for the power elements 2 to 7 of the inverter. The gate circuits 8 to 13 of the power element turn on and off the power elements 2 to 7 according to the on / off command signal, so that the DC voltage Vbus rectified by the converter 1 is converted into the voltage commands Vu *, Vv *, Vw.
It is applied to each phase of the motor 15 with a duty proportional to *. As described above, the phase current of each phase of the motor 15 is
The current commands Iu * and Iv * are controlled to match.

FIG. 5 is a block diagram showing another circuit configuration of an inverter control device using a conventional technique. In the figure, blocks having the same functions as those in FIG. 4 are given the same numbers. In the device of FIG. 5, the voltage drops Vsu and Vsv of the current detection resistors 16 and 17 are the serial output type A / D converter 2
The signals 3 and 24 are converted into digital signals SigDu and SigDv. Next, SigDu and SigDv are photocouplers 2
It is insulated by 5 and 26 from the phase potential of the inverter and input to the shift registers 27 and 28 to be converted into parallel data. Shift registers 27, 28
Is output to the current control circuit 22, and the phase currents of the motor phases are the current commands Iu * and Iu, as in the control device of FIG.
Controlled to match v *.

[0004]

In the inverter control device for driving and controlling the motor, the gain error of the isolation amplifier 20 and its offset when the currents of the phase currents Iu and Iv are detected cause a ripple in the output torque of the motor 15. , It is necessary to make it as small as possible. In the above-described inverter control device using the conventional technique, the analog output isolation amplifier 1 is used to detect the output currents Iu and Iv of the inverter.
8 and 20 and the A / D converters 19 and 21 are used in combination, the gain error and offset of the detected current are caused by the isolation amplifiers 18 and 20 and the A / D converter 1.
Since it depends on the sum of the product of the gain error and the offset of both 9 and 21, it is difficult to keep both the gain error and the offset of both components small. On the other hand, as a measure to avoid this, as shown in FIG.
A configuration using only the / D converters 23 and 24 is also possible. However, when such a configuration is used, the A / D
There is a problem in that when noise is superimposed on the serial signals of the converters 23 and 24, a large error (1/2 of full scale when noise is received during MSB bit transfer) is included. The present invention has been made to solve the above problems, and provides an inverter control device capable of suppressing a gain error and an offset at the time of detecting a current, and reducing a torque ripple of a motor to be driven. Has an aim.

[0005]

A current detecting resistor is inserted in series with an output circuit of an inverter for converting DC power into AC power for driving a motor by a power element having a gate circuit, and a current detecting resistor is generated at both ends of the current detecting resistor. An inverter control device for detecting a phase current of a motor from a potential difference and performing feedback control of driving of a motor, wherein a sigma-delta modulator for converting a potential difference generated across the current detection resistor into a sigma-delta modulated digital signal, An electrically insulating coupler for electrically insulating and transmitting the digital signal; a digital filter for demodulating the transmitted signal;
And a control signal generation circuit for controlling the gate circuit of the inverter based on the output of the digital filter.

In the inverter control device according to the present invention, the sigma-delta modulator can be used as a component for determining the gain error and the offset when the output current of the inverter is detected, and therefore the conventional isolation amplifier and the A / D converter can be used. It is possible to detect a current with a smaller gain error and offset as compared with the inverter control device including the above, and it is possible to reduce the torque clip of the motor to be driven.

[0006]

1 is a block diagram showing an embodiment of a circuit of an inverter control device according to the present invention. In FIG. 1, blocks having the same functions as those in FIG. 4 are given the same numbers. Converter 1, power elements 2 to 6, gate circuit 8 to
13, the configuration of the PWM signal generation circuit 14 and the motor 15,
Since it is the same as the conventional example shown in FIG. 4, description thereof will be omitted. Voltage drop Vsu, Vsv generated across the current detection resistors 16 and 17
Is input to the ΣΔ modulators 30 and 31 and converted into signals SigSu and SigSv having an on-off duty proportional to the voltage. Next, SigSu and SigSv are insulated from the phase potential of the inverter by the photocouplers 25 and 26 as electrically insulating couplers that electrically insulate and transmit the input signal, and are input to the digital filters 32 and 33 and demodulated. , Parallel digital signals Iu and Iv. The PWM signal generation circuit 14 and the digital filters 32 and 33 form a digital integrated circuit 34. The digital signals Iu and Iv are supplied to the current control circuit 22.
The control is performed so that the phase current of each phase of the motor matches the current commands Iu *, Iv * from the host control circuit, similarly to the control device having the configuration of FIG. In addition, the PWM signal generation circuit 14 and the current control circuit 22
Serves as a control signal generation circuit that controls the gate circuits 8 to 13 of the inverter based on the outputs of the digital filters 32 and 33.

Next, the configurations and operations of the ΣΔ modulators 30 and 31 and the digital filters 32 and 33 will be described with reference to the block diagram shown in FIG. 2 and the signal waveforms of the respective parts shown in FIG. The ΣΔ modulator 30 employs a modulation method called second-order sigma-delta modulation. In FIG. 2, the output signal SigSu is input to the 1-bit D / A converter 35, and the voltage output from the D / A converter 35 is + Vref when SigSu is "1", and In the case of "0" -changes to Vref. The input voltage Vsu is calculated by the subtractor 36.
The difference from the output of the D / A converter 35 is input to the integrator 37. The output of the integrator 37 is input to the subtractor 38, the difference from the output of the D / A converter 35 is obtained again, and the input to the integrator 39. The output of the integrator 39 is output by the comparator 40. Compared to 0V. The output of the comparator 40 is sampled by the latch 42 at every cycle T of the clock CLOCK1 output from the oscillator 41, and becomes the output signal SigSu. With the above-described configuration, feedback is performed so that the output of the integrator 39 approaches 0V, and as shown in FIG. 3C, the output signal S having an on-off duty proportional to the input voltage Vsu.
igSu is obtained.

On the other hand, the output signal SigSu contains high-frequency quantization noise as shown in FIG. 3 (d). For this reason, the digital filter 32 removes the quantization noise above the cutoff frequency fc by the transfer characteristic shown in FIG. 3 (e), and in the configuration example of FIG. 2, this transfer is performed by an n-stage FIR (finite impulse response) filter. The characteristics are realized. The digital filter 32 is a clock CLOCK synchronized with the clock CLOCK1 in the ΣΔ modulator 30 by a PLL (phased lock loop) circuit 43 using the signal change point of SigSu passing through the photocoupler 25.
Generates 2. The shift register 44 outputs the output signal SigSu.
Are sampled by CLOCK2 and sequentially shifted. The coefficient table 45 incorporates a coefficient a (k) having a multi-bit precision corresponding to each output bit Q (n-k) of the shift register, and when Q (n-k) is "1", a (k). Is output to the accumulator 46 when Q (n−k) is “0”. The accumulator 46 calculates the sum of the data from the coefficient table 45,
The signal Iu is output to the current control circuit 22. Here, the signal Iu is a general formula of the FIR filter, Σ {a (k)
XQ (n−k)}, the target transfer characteristic can be obtained by appropriately setting the coefficient a (k).

[0009]

As described above, according to the inverter control device of the present invention, the components that determine the gain error and the offset when the output current of the inverter is detected are Σ.
Since it is limited to the delta modulator, the conventional isolation amplifier and A / D
Compared with an inverter control device including a converter, it is possible to detect a current with a smaller gain error and offset, and it is possible to reduce the torque ripple of the motor to be driven, which is a remarkable effect.

[0010]

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a circuit of an inverter control device according to the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a ΣΔ modulator and a digital filter of the inverter control device according to the present invention.

FIG. 3 is a signal waveform of each part in FIG.

FIG. 4 is a block diagram showing an example of a circuit of an inverter control device according to a conventional technique.

FIG. 5 is a block diagram showing another circuit example of an inverter control device according to a conventional technique.

[Explanation of symbols]

 1 Converter 2-7 Power element 8-13 Gate circuit 14 PWM signal generation circuit 15 Motor 16,17 Current detection resistor 18,20 Insulation amplifier 19,21 A / D converter 22 Current control circuit 23,24 A / D converter 25, 26 Photocoupler 27, 28 Shift register 30, 31 Σ / Δ modulator 32, 33 Digital filter 34 Digital integrated circuit 35 D / A converter 36, 38 Subtractor 37, 39 Integrator 40 Comparator 41 Oscillator 42 Latch 43 PLL Circuit 44 Shift register 45 Coefficient table 46 Accumulator

Claims (2)

[Claims] 1. A current detecting resistor is serially inserted in an output circuit of an inverter that converts direct-current power into alternating-current power for driving a motor by a power element having a gate circuit, and a potential difference between both ends of the current detecting resistor is applied to the motor. In an inverter control device that drives a motor by detecting a phase current and performing feedback control, a sigma-delta modulator that converts a potential difference across both ends of the current detection resistor into a sigma-delta modulated digital signal, and the digital signal An electrically insulative coupler for electrically insulating and transmitting, a digital filter for demodulating the transmitted signal, and a control signal generating circuit for controlling the gate circuit of the inverter based on the output of the digital filter. Characteristic inverter control device. 2. The inverter control device according to claim 1, wherein the electrically insulative coupler is a photocoupler.