JP3220570B2 - Inverter control device - Google Patents

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 driving inverter control device using the prior art. After the three-phase AC power is converted into a DC voltage of an appropriate voltage by the converter 1, the power elements 2, 3, 4, 5, 6, 7 are connected in parallel by three sets of two connected in series.
The DC power is converted into AC power for driving a motor. Gate circuits 8, 9, 10, 11, 12, and 13 are connected to the power elements 2, 3, 4, 5, 6, and 7, respectively. 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 insulating 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 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. Analog signals SigAu and SigAv are A / D converters 1
The signals are converted into digital values by 9 and 21 and input to the current control circuit 22. The current control circuit 22 obtains a current deviation of each phase from the current commands Iu * and Iv * input from the higher-level control circuit and the detected phase currents Iu and Iv, and performs proportional and integral amplification on each of the current deviations. It outputs voltage commands Vu *, Vv *, Vw * to be applied to the phase. Voltage command V
u *, Vv * and Vw * are PWM signals having an on / off duty proportional to the command value by the PWM signal generation circuit 14.
The signal is converted into a signal, and a dead time for preventing a short circuit of the arm is added to the signal to be an on / off command signal for the power elements 2 to 7 of the inverter. The gate circuits 8 to 13 of the power devices turn on and off the power devices 2 to 7 in accordance with the on / off command signals, thereby converting the DC voltage Vbus rectified by the converter 1 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
Control is performed so as to match current commands Iu * and Iv *.

FIG. 5 is a block diagram showing another circuit configuration of an inverter control device using the prior art. In the figure, blocks having the same functions as those in FIG. 4 are denoted by the same reference numerals. In the device shown in FIG. 5, the voltage drops Vsu and Vsv of the current detection resistors 16 and 17 correspond to the serial output type A / D converter 2.
The digital signals are converted into digital signals SigDu and SigDv by 3 and 24, respectively. Next, SigDu and SigDv are Photocoupler 2
5 and 26 are insulated 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 input to the current control circuit 22, and the phase current of each phase of the motor is converted into the current command Iu *, I
It is controlled to match v *.

[0004]

In an inverter control device for driving and controlling a motor, a gain error and an offset of the insulating amplifier 20 at the time of detecting currents of the phase currents Iu and Iv cause a ripple in an output torque of the motor 15. , Need to be as small as possible. In the inverter control device using the prior art, an analog output isolation amplifier 1 is used to detect the inverter output currents Iu and Iv.
8 and 20 and the A / D converters 19 and 21 are used in combination, the gain error and the offset of the detected current are reduced by the isolation amplifiers 18 and 20 and the A / D converter 1.
It depends on the sum of the product of the gain errors of both 9 and 21 and the offset, and 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, A / D
There is a problem that when noise is superimposed on the serial signals of the converters 23 and 24, a large error (1/2 of the full scale when noise is received during transmission of the MSB bit) is included. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an inverter control device capable of suppressing a gain error and an offset at the time of current detection to a small value and reducing a torque ripple of a driving motor. The purpose is.

[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 is generated at both ends of the current detecting resistor. By detecting the phase current of the motor from the potential difference and performing feedback control,
An inverter control device for driving the over motor, the sigma-delta modulator for converting the potential difference across the current detecting resistor to the sigma-delta modulated digital signal without weighting, the digital signal electrically insulating transmission An electrically insulating coupler, and the sigma-delta modulator
Is configured as a separate integrated circuit, said electrically insulating coupler
A digital filter for demodulating the signal transmitted from the
A control signal generating circuit for controlling a gate circuit of the inverter based on the output of the digital filter.

In the inverter control device according to the present invention, since the components for determining the gain error and the offset when detecting the output current of the inverter can be a sigma-delta modulator, the conventional isolation amplifier and A / D converter can be used. compared to the inverter controller with a possible small current detecting a gain error and offset, it is possible to reduce the motor torque Cripple is driven. Also,
Digital filters are collected separately from the sigma-delta modulator.
Because it is configured as an integrated circuit, the power element is usually
Do not place the product close to (on a wiring board through which a large current can flow).
Sigma-delta modulators and electrically insulating couplers that must be
Away from, for example, next to the control CPU on the control board
Digital fill in custom LSI package
Design and production.
The degree of freedom described above can be improved, and
It is easy to change. On the other hand, the sigma-delta modulator
Output a digital signal without weighting.
Using a serial signal output type A / D converter
That is, a weighted digital signal is output.
Sigma-delta modulators and electrically insulating coupling
Devices configured as separate integrated circuits from the
Noise in the transmission path of the output signal to the digital filter
The effect of noise is extremely small.

[0006]

FIG. 1 is a block diagram showing an embodiment of a circuit of an inverter control device according to the present invention. 1, blocks having the same functions as those in FIG. 4 are denoted by the same reference numerals. Converter 1, power elements 2 to 6, gate circuit 8 to
13, the PWM signal generation circuit 14, and the configuration of the motor 15
The description is omitted because it is the same as the conventional example shown in FIG. Voltage drops Vsu, Vsv generated at both ends of the current detection resistors 16 and 17
Are input to the ΣΔ modulators 30 and 31 and are 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 photocouplers 25 and 26 as electrically insulating couplers that electrically insulate and transmit the input signal, input to digital filters 32 and 33, and demodulated. , And parallel digital signals Iu and Iv. The PWM signal generating circuit 14 and the digital filters 32 and 33 constitute a digital integrated circuit 34. The digital signals Iu and Iv are supplied to the current control circuit 22.
The control is performed such that the phase current of each phase of the motor matches the current commands Iu * and Iv * from the higher-level control circuit, similarly to the control device having the configuration of FIG. Further, the PWM signal generation circuit 14 and the current control circuit 22
Has a function as a control signal generation circuit for controlling the gate circuits 8 to 13 of the inverters 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 each section 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 a 1-bit D / A converter 35. The voltage output from the D / A converter 35 is + Vref when SigSu is "1". If it is "0", it changes to -Vref. The input voltage Vsu is calculated by the subtractor 36.
And 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 a subtractor 38, and the difference from the output of the D / A converter 35 is obtained again and input to an integrator 39. The output of the integrator 39 is output by a comparator 40. It is compared with 0V. The output of the comparator 40 is sampled by the latch 42 every cycle T of the clock CLOCK1 output from the oscillator 41, and becomes an output signal SigSu. With the above configuration, feedback is performed so that the output of the integrator 39 approaches 0 V, 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. For this reason, the digital filter 32 removes quantization noise higher than the cutoff frequency fc by the transfer characteristic shown in FIG. 3 (e). 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 has a clock CLOCK synchronized with the clock CLOCK1 in the ΣΔ modulator 30 by a PLL (Phase Locked Loop) circuit 43 using a signal change point of SigSu via the photocoupler 25.
Generate 2. The shift register 44 outputs the output signal SigSu.
Are sampled by CLOCK2 and sequentially shifted. The coefficient table 45 has a built-in coefficient a (k) having a plurality of bits of precision corresponding to each output bit Q (nk) of the shift register. When Q (nk) is "1", a (k) Is output to the accumulator 46 when Q (nk) is “0”. The accumulator 46 calculates the sum of the data from the coefficient table 45,
The signal is output to the current control circuit 22 as a signal Iu. Here, the signal Iu is a general expression of the FIR filter, Σ ｛a (k)
× Q (n−k)}, the desired transfer characteristic can be obtained by appropriately setting the coefficient a (k).

[0009]

As described above, according to the inverter control apparatus of the present invention, the components for determining the gain error and the offset when detecting the output current of the inverter are as follows.
Because it is limited to the Δ modulator, the conventional isolation amplifier and A / D
As compared with an inverter control device including a converter, current detection with a small gain error and a small offset is possible, and torque ripple of a motor to be driven can be reduced . Also, change the digital filter to sigma-delta
To be configured as an integrated circuit separate from the controller.
In a place close to the normal power element (a wiring board through which large current can flow)
Sigma-delta modulator that must be placed on the board)
Or a place away from the electrically insulating coupler, for example, on the control board
In a custom LSI package adjacent to the control CPU
It is possible to design such as installing a digital filter in
Digital and digital
It is easy to change the characteristics of the filter. On the other hand, sig
Digital signal without weight by ma-delta modulator
Output, the conventional serial signal output type A / D converter
Configuration using barter, that is, weighted digital
Sigma-delta modulator
Or an integrated circuit separate from them
Of output signal to digital filter
This has a remarkable effect that the influence of noise on the path is extremely small .

[0010]

[Brief description of the 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. 2;

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

FIG. 5 is a block diagram showing another example of the circuit of the inverter control device according to the related art.

[Explanation of symbols]

 DESCRIPTION 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/48 G05F 1/10 H02P 7/63

Claims (2)

(57) [Claims] 1. A current detection 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 potential difference between both ends of the current detection resistor is used to detect a motor current. In an inverter control device that drives a motor by detecting a phase current and performing feedback control, a potential difference generated between both ends of the current detection resistor is weighted by sigma-delta modulation.
A sigma-delta modulator for converting the have a digital signal, an electrically insulating coupler for electrically insulating transmitting the digital signal, the separate integrated times the sigma-delta modulator
A digital filter configured as a path for demodulating a signal transmitted from the electrically insulating coupler, and a control signal generating circuit for controlling a gate circuit of the inverter based on an output of the digital filter. Inverter control device. 2. The inverter control device according to claim 1, wherein the electrically insulating coupler is a photocoupler.