JPS6126481A - Control circuit for converter - Google Patents

Abstract

PURPOSE:To stably operate by momentarily resetting the voltage deviation integrated amount of a converter control circuit to the deceleration of an induction motor, and accelerating the switching time from power drive to regenerative drive. CONSTITUTION:One terminal of a converter 2 is connected with an AC power source 1, and the other terminal is connected through an inverter 4 with a load 5. A proportional controller 6 multiplies the prescribed proportional multiplier by the difference between the voltage of the other terminal of the converter 2 and the voltage command, and an integrating controller 7 multiplies the prescribed integrating constant by the integrated amount of the difference between the voltage of the other terminal of the converter 2 and the voltage command. The outputs of the controllers 6, 7 are added, and input to a phase angle instruction unit 8. The unit 8 controls a firing command supplied to the converter 2 so as to reset the integrated amount of the controller 7 to zero when the polarity of the difference between the voltage of the other terminal of the converter 2 and the voltage command varies to set the detected difference to zero.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control circuit for a reversible thyristor converter circuit used in an inverter device.

[Prior art]

Conventionally, there has been a control circuit of this type as shown in FIG. In the figure, 1 is a three-phase AC power supply, 2 is a converter circuit consisting of a thyristor and performs power and regeneration operations, 3 is a capacitor that smoothes the output voltage of the converter circuit 2,
4 is an inverter circuit that converts the voltage smoothed by the capacitor 3 into AC having a desired frequency, 5 is an induction motor, and 6 is a voltage command Vref for the converter circuit 2 and a voltage VDC fed back from the converter circuit 2.
Proportional control unit that multiplies the difference vK by the proportional constant Kp, T is the difference V
An integral control section 8 multiplies the integral amount by an integral constant KI, and 8 is a converter circuit 2 from the outputs of the proportional control section 6 and the integral control section 7.
This is the phase angle command unit that determines the firing angle of the thyristor.

Next, the operation will be explained. When the phase angle command unit 8 commands a firing angle of 9, the converter circuit 2 enters the 9 firing mode.
The alternating current of the three-phase AC power supply 1 is rectified by an internal, negative-side thyristor (not shown), and the rectified voltage is smoothed by a capacitor 3.

On the other hand, when the phase angle command section 8 commands a regenerative firing angle, the converter circuit 2 enters the regeneration mode and converts the electric charge charged in the smoothing capacitor 3 into alternating current by a regeneration-side thyristor (not shown). Return to three-phase AC power supply 1. Smoothing capacitor 3 smoothes the voltage across converter circuit 2 and applies the smoothed DC voltage to inverter circuit 4 .

The DC voltage smoothed by the inverter circuit 4 capacitor 3 is switched by an internal transistor to convert it into three-phase AC having a desired frequency, and the induction motor 5 is rotated by this three-phase AC.

The voltage of the capacitor 3 (converter voltage) VDC is compared with a voltage command Vref determined by the rotation speed of the induction motor 5 by a proportional control section 6 and an integral control section 7, and the firing angle or regeneration is determined by a phase angle command 8. The firing angle is determined and input to the converter circuit 2 as the firing angle. Here, the proportional control section 6, the integral control section 7, and the phase angle command section 8 are composed of a microprocessor, and FIG. 2 shows the processing thereof in the form of a flowchart. First, the difference V between the voltage command Vref and the voltage VDC of the capacitor 3 is determined. Next, KPM is the difference V multiplied by the proportionality constant KP, and the integral amount ΣVK is the integral constant multiplied by summer! ΣV is added, and if the addition result is positive, it is determined that it is a power line, and if it is negative, it is determined that it is a regeneration,
Outputs a power line or regenerative firing angle command corresponding to the voltages of IK, V+K, and Ev1.

FIG. 3 shows the waveform of the converter voltage when the speed of the induction motor 5 is reduced. Since it is necessary to return the voltage generated from the induction motor 5 to the three-phase AC power supply 1, vref
The value of VDC=v becomes negative from the moment the speed is lowered by the command "ref. However, since ΣV does not become negative immediately, there is a time delay before the regeneration program is executed, as shown in Figure 3. The voltage VDC momentarily becomes a large value.

Since the conventional converter control circuit is configured as described above, the converter voltage increases to a large value when the rotation of the induction motor is reduced, so there is a drawback that the stability of the converter voltage is impaired.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it resets the voltage deviation integral amount of the converter control circuit at the moment of deceleration of the induction motor, thereby reducing the switching time from power to regeneration. The purpose of this invention is to provide a converter control circuit that can provide more stable operation.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. A block diagram of the converter circuit according to the present invention is shown in FIG. 1 described above, but the operation of the phase command section 8 is different from that of the conventional converter circuit as described below. FIG. 4 shows a flowchart of control processing according to the present invention. In the figure, first, it is determined whether the speed command value of the current sampling is lower than the speed command value of the induction motor 5 of the previous sampling. Jesus (y
), the difference V between the speed command and the speed of the induction motor 5, that is, when the polarity of the bias changes from positive to negative or from negative to positive, the integral amount ΣV of the difference V is reset.

In this way, Ev is reset by capturing the moment when the speed command starts to decrease and the actual speed of the induction motor 5 starts to decrease. Next Kvref-vDC=v and KpV+KlΣv-v
Calculate s. Since ΣV is zero, if the difference V is determined to be negative, Kpv 1KiEV=V9 will also be negative, and the firing angle will be the command %JL.

On the other hand, when it is positive, the regenerative firing angle is commanded, and the delay time for reducing ΣV can be brought closer to zero, and the voltage when the speed of the induction motor 5 is lowered as shown in Fig. 5. VDC
The overhang can be reduced and the converter voltage can be stabilized.

In the above embodiment, a case is shown in which the phase command section 8 is a microprocessor, but a hardware circuit composed of an operational amplifier, a resistor, and a capacitor can also produce the same effect.

〔Effect of the invention〕

According to the above invention, when the slip of the induction motor changes from positive to negative, pressure is applied to reset the integral amount of slip to zero, so the converter circuit can be stabilized and the accuracy This has the effect of providing high induction motor control.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the converter control circuit, Fig. 2 is a flow chart showing the operation of a conventional converter control circuit, and Fig. 3 is a block diagram showing the converter control circuit.
Fig. 4 is a characteristic diagram showing the relationship between the speed command and converter voltage of a conventional converter control circuit, Fig. 4 is a flowchart of the operation of the converter control circuit according to an embodiment of the present invention, and Fig. 5 is a characteristic diagram showing the relationship between the speed command and converter voltage of a conventional converter control circuit. FIG. 3 is a characteristic diagram showing the relationship between converter voltage waveforms. 1...Miphase AC power supply, 2...Converter circuit, 3.
...Capacitor, 4...Inverter circuit, 5...
Induction motor, 6... proportional control section, 7... integral control section, 8... phase angle command section. In addition, in the figures, the same reference numerals indicate the same or equivalent parts 0 Patent applicant Mitsubishi Electric Corporation Figure 2 Figure 3 Figure 4 Figure 5 Procedural amendment (voluntary)

Claims (1)

[Claims] A proportional control section that multiplies the difference between the voltage at the other end of the converter, one end of which is connected to an AC power source and the other end of which is connected to a load via an inverter, and the voltage command by a predetermined proportionality constant, and an integral of the difference. an integral control unit that multiplies the amount by a predetermined integral constant; and an ignition command that is supplied to the converter so as to reset the integral amount to zero and reduce the detected difference to zero when the polarity of the difference changes. A converter control circuit equipped with a phase angle command section that controls.