JPH05111261A - Current detector - Google Patents

Abstract

PURPOSE:To provide a current detector which can remove spikelike noise generated at an output of an insulating amplifier at a moment that a phase voltage is abruptly varied while a current detecting delay is limited to a minimum limit in a controller using an inverter. CONSTITUTION:A pulse synchronized with a variation in a phase voltage is generated from a holding signal generator 20 based on an ON/OFF signal to a power element (e.g. power elements Tr1, Tr2 of an inverter of a phase to be measured and polarity of a phase current. And, noise is removed by stopping a sampling operation of a secondary side of an insulating amplifier 10 by using a gate circuit 13 during a period of ON of a pulse signal sent from the generator 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device used in a motor control device using an inverter, and more particularly to a current detecting device suitable for use in converting a detected current value into a digital value and feeding it back.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an example of a conventional current detecting device. In the drawing, a simple block and signal relating to a U phase are mainly shown, and a current detecting device relating to a V phase is omitted. The PWM circuit 6 uses the signals sigtrl, sig having pulse widths proportional to the applied voltage command to the motor 5.
tr2 (see FIG. 2) is sent to the base drive circuits 1 and 2 of the U-phase arm of the inverter. The base drive circuits 1 and 2 are provided with corresponding power elements Trl and Tr.
2 is a signal sent from the PWM circuit 6
It is turned on / off according to igtr2, and the U-phase voltage is alternately changed to the input potentials VH and VL of the inverter as shown in FIG.

A U-phase current shown in FIG. 2 flows through the motor 5 according to the potential difference between the U, V and W phases, and a voltage drop proportional to this current is generated across the detection resistor 3. This voltage is input to the isolation amplifier 10 and passes through the isolation transformer T2 by being periodically interrupted by the switch SW1 at the frequency of the oscillator 12. The output signal of the isolation transformer T2 is sampled and demodulated by the switch SW2, then amplified by the buffer amplifier 11 and sent to the A / D (analog-digital) converter 7 (the output waveform of the isolation amplifier 10 is shown in FIG. 2). Shown). The output of the isolation amplifier 10 is converted into a digital value by the A / D converter 7 and used for control.

[0004]

In the conventional current detecting device, spike-like noise appears in the output of the isolation amplifier at the moment when the U-phase voltage sharply changes as shown by the waveform shown in FIG. There was a problem. This is mainly due to capacitive coupling between the input and output of the transformer T2 used in the isolation amplifier, and changes in the phase voltage are differentiated and superimposed on the output. On the other hand, the output of the isolation amplifier is A / D
Since the noise is sampled by the converter, when the spike-shaped noise portion is sampled, the detected value is greatly deviated.

The first conceivable countermeasure against this is the improvement of the transformer, but generally, the change of the phase voltage is several hundreds V / μ.
However, since the minimum voltage to be detected is several mV, it is difficult to suppress the coupling capacitance to a value that does not affect the size of the transformer while keeping it small. Next, there is a method of removing the spike component by a filter, but in this case, a phase delay occurs in the detection, and the frequency characteristic deteriorates when the current detection value is used for feedback control.
As described above, in the conventional current detection device, there is no effective means for removing the noise generated by the phase voltage change while keeping the detection delay to a minimum. The present invention has been made under the above circumstances, and an object of the present invention is to provide a current detection device capable of removing noise generated by a phase voltage change while keeping a current detection delay to a minimum. is there.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a current detecting device for detecting a phase current of a motor driven by an inverter using a detection resistor and an insulation amplifier inserted in series with a motor line. The purpose of the above is to change the output potential of the phase inverter based on the ON / OFF command signal for each power element of the inverter arm connected to the motor wire of the phase to be measured and the polarity signal of the phase current. This is achieved by providing hold signal generating means for stopping the sampling operation of the secondary voltage of the transformer of the isolation amplifier only for a period.

[0007]

According to the current detection device of the present invention, the output of the isolation amplifier is held only during the period when the phase voltage changes, so that the current detection value is not affected by the spike.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an example of the current control device of the present invention in correspondence with FIG. 5, and the same components are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, a hold signal generating circuit 20 and a gate circuit 13 in the isolation amplifier 10 are added to the conventional current detecting device. The hold signal generation circuit 20 is a circuit that predicts a change in the phase voltage and generates a hold signal holdu that is a pulse synchronized with the change. First, as a method of predicting the change in the phase voltage, the U phase is taken as an example. State. In FIG. 2, looking at the U-phase voltage () and the signals sigtr1, sigtr2 (,) for the U-phase power devices Tr1, Tr2, when the direction of the U-phase current is from the inverter to the motor 5, the U-phase voltage ( ) Substantially coincides with the change point of the signal sigrtr () of the power element Tr1. In the opposite case, the change point of the U-phase voltage () substantially coincides with the change point of the signal sigr2 () of the power element Tr2. I know that In the present invention, by utilizing this property, the power element Tr
Changes in the U-phase voltage are predicted from the signals sigrtr1 and sigtr2 for 1 and Tr2 and the current polarity signal signu.

FIG. 3 is a block diagram showing an example of the hold signal generating circuit 20, and FIG. 4 is a time chart of each signal in this circuit. The signals sigtr1, s sent from the PWM circuit 6 to the power elements Tr1, Tr2
igtr2 is a signal d delayed by the number of clocks designated by the oscillator 23 (three clocks in the example of FIG. 4) by the digital delay circuits 21 and 22 in the hold signal generation circuit 20.
eltr1 () and deltr2 (). Input / output signals deltr1, sigtr1 and deltr of the digital delay circuit 21 and the digital delay circuit 22
2, sigrtr2 are sent to the exclusive OR circuits 24 and 25, and the pulses chgtr1 () and ch synchronized with the change point
It becomes gtr2 () and is sent to the selector circuit 26.

The selector circuit 26 causes a pulse chgtr when the current polarity signal signu () is +.
1 is selected, and in the case of-, the pulse chgtr2 is selected and sent to the gate circuit 13 as the hold signal holdu (). And using the gate circuit 13,
A signal chop2 output by the oscillator 12 in the isolation amplifier 10 for sampling on the secondary side is changed to a hold signal ho.
Stop while ldu is on. As described above, sampling of the isolation amplifier 10 is stopped while the U-phase voltage is changed, so that the output of the isolation amplifier 10 does not include the spike quiz as shown in FIG. In addition,
In the present embodiment, the current polarity signal signu is obtained from the output of the A / D converter (determined by the previous conversion result), but it can be obtained from the polarity of the current control current command value.

[0011]

As described above, according to the current detection device of the present invention, it is possible to eliminate the error in the current detection value due to the change in the voltage of the phase to be measured (the error due to the insufficient common-mode voltage removal performance of the isolation amplifier). Moreover, since the sampling is stopped only at a specific timing, the influence of the measurement time delay is small. Therefore, when the current detection device is used in a feedback loop for current control, good current controllability with a high response frequency can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a current detection device of the present invention.

FIG. 2 is a diagram showing an example of a time chart of an insulation amplifier input / output signal in the device of the present invention and the conventional current detection device.

3 is a block diagram showing an example of a hold signal generation circuit of FIG. 1. FIG.

FIG. 4 is a diagram showing an example of a time chart of each signal in the hold signal generation circuit of FIG.

FIG. 5 is a block diagram showing an example of a conventional current detection device.

[Explanation of symbols]

 13 gate circuit 20 hold signal generating circuit

Claims (1)

[Claims] 1. A current detecting device for detecting a phase current of a motor driven by an inverter using a detection resistor and an insulation amplifier inserted in series in the motor line, and the inverter connected to the motor line of the phase to be measured. A hold that stops the sampling operation of the secondary side voltage of the transformer of the isolation amplifier only during the period when the output potential of the phase inverter changes based on the ON / OFF command signal for each power element of the arm and the polarity signal of the phase current. A current detecting device comprising a signal generating means.