JPH1141934A - Controller of pwm converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the insulation breakdown of windings of an induction motor by constructing a controller in such a mechanism that a DC voltage command value to be controlled may be the one obtained by multiplying a peak value of the line voltage of a polyphase AC power supply by a specified factor. SOLUTION: A PWM converter control circuit 8 reads the DC voltage of a DC capacitor 4 and the voltage and current of a polyphase AC power supply through a supply voltage converter 6 and a supply current converter 7 and controls them to desired values. Generally, the DC voltage of the DC capacitor 4 is kept at a command value output from a DC voltage command generator 9 and the current of the polyphase AC power supply is so controlled that the power factor may be 1 and a distortion factor of the current may be minimum. By this method, a peak value of the voltage to be applied to windings of an induction motor can be lowered and thereby the insulation breakdown can be prevented. Furthermore, as the DC voltage can be so controlled that it may not be a specified value or below when the supply voltage decreases, there is no decline in controllability caused by the decline in DC voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to DC voltage control of a PWM converter for converting polyphase alternating current to direct current.

[Prior art]

FIG. 5 is a main circuit configuration diagram of a commonly used three-phase voltage type PWM converter. In FIG. 5, a three-phase voltage type PWM converter bridge, 1 is a three-phase AC power source, and 2 is an AC Reactor, 4 is a DC capacitor,
5 is a load. The function expected of this PWM converter is to convert three-phase alternating current into direct current, but also to control the DC voltage so as not to increase more than necessary. It is extremely difficult to make the DC voltage of the PWM converter shown in FIG. 5 lower than the full-wave rectified voltage of the three-phase AC voltage. Therefore, in the control device of the conventional PWM converter, the command value of the DC voltage is set to a value further allowing the maximum value of the line voltage in consideration of the variation of the three-phase AC voltage.

[Problems to be solved by the invention]

[0003] The DC voltage thus determined is usually a very high value. For example, a general AC voltage 44
DC voltage is about 720V in 0V class PWM converter
Set to about. In this case, the PWM converter
In a system in which an M inverter is connected to drive an induction motor, a rectangular wave having a peak value of 720 V is constantly applied to the motor. Also, if the wiring length between the PWM inverter and the induction motor is long, electric vibration is caused between the inductance of the wiring and the stray capacitance between the winding of the induction motor and the frame, so that a higher voltage is applied to the induction motor. As a result, the insulation of the winding of the induction motor may be broken down.

[Means for Solving the Problems]

[0004] As means for solving these problems, the present invention sets the command value of the DC voltage to be controlled to a value obtained by multiplying the peak value of the line voltage of the polyphase AC by a predetermined coefficient. Constitute. That is, the command value of the DC voltage may be set to the minimum necessary DC voltage that can be PWM controlled according to the AC voltage at that time. In this case, the converter output voltage changes. However, recent PWM inverters have a function of keeping the output voltage constant even when the DC voltage changes, so it is necessary to keep the DC voltage constant. Absent. Furthermore, the command value of the DC voltage to be controlled, a value obtained by multiplying the peak value of the line voltage of the polyphase AC by a predetermined coefficient,
It is configured to select the higher one of a predetermined value and another predetermined value.

【Example】

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the present invention. In the figure, 1 is a polyphase AC power supply, 2 is an AC reactor, 3
Is a polyphase PWM converter bridge, 4 is a DC capacitor, 5 is a DC load, 6 is a power supply voltage converter, 7 is a power supply current converter, 8 is a PWM converter control circuit, and 9 is a DC voltage command generator.

The PWM converter control circuit 8 converts the DC voltage of the DC capacitor 4 and the voltage and current of the polyphase AC power supply into
They are read via the power supply voltage converter 6 and the power supply current converter 7, respectively, and are controlled to desired values. Generally, the DC voltage of the DC capacitor 4 is maintained at a command value output from the DC voltage command generator 9, and the current of the polyphase AC power supply is controlled so as to minimize the power factor of 1, and further minimize the distortion factor. I do.

FIG. 2 shows a DC voltage command generator 9 shown in FIG.
3 is a block diagram showing a first detailed example of FIG. In the figure, 21 is a three-phase full-wave rectifier circuit, 22 is a peak value holding circuit, and 23 is a coefficient generator. The three-phase full-wave rectifier 21 has its input 121
Is subjected to full-wave rectification, and the peak value holding circuit 22 holds the peak value. This is constituted by a first-order lag filter circuit having a long time constant, for example. The coefficient generator 23 multiplies the output of the peak value holding circuit 22 by a predetermined coefficient and outputs the result to 122.

FIG. 3 shows a DC voltage command generator 9 shown in FIG.
FIG. 9 is a block diagram showing a second detailed example of FIG. In FIG.
Reference numerals 22 and 23 have the same functions as those shown in FIG. 2, 24 is a minimum voltage setter, and 25 is a priority circuit. Priority circuit 25
Compares the output of the coefficient generator 23 with the output of the lowest voltage setter 24, and outputs the larger one to 122. Therefore, the relationship between the AC voltage and the DC voltage command value in the second detailed example is as shown in FIG. The feature of the detailed example of FIG. 3 that determines the lower limit of the DC voltage is that even if the AC voltage decreases, the output voltage of the PWM inverter is maintained at a predetermined value and does not hinder the control of the induction motor connected to the PWM inverter. In particular, the effect is exerted when performing vector control.

【The invention's effect】

As described in detail above, according to the present invention, the peak value of the voltage applied to the winding of the induction motor can be effectively reduced, and its dielectric breakdown can be prevented. In addition, when the power supply voltage is reduced, the DC voltage can be controlled so as not to fall below a predetermined value.If the present invention is applied to a vector control drive, it is possible to prevent the control performance from being reduced due to the DC voltage reduction. The effect is enormous.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a block diagram showing a first detailed example of the DC voltage command generator 9 shown in FIG.

FIG. 3 is a block diagram showing a second detailed example of the DC voltage command generator 9 shown in FIG.

FIG. 4 is a diagram showing characteristics of a second detailed example of the DC voltage command generator 9 shown in FIG.

FIG. 5 is a configuration diagram of a main circuit of a generally used three-phase voltage type PWM converter.

[Explanation of Codes] 1. Multi-phase AC power supply AC reactor 3. 3. Multi-phase PWM converter bridge DC capacitor 5. DC load 6. Power supply voltage converter 7. Power supply current converter 8. 8. PWM converter control circuit DC voltage command generator 21. 3-phase full-wave rectifier circuit 22. Peak value holding circuit 23. Coefficient generator 24. Minimum voltage setting device 25. Priority circuit

Claims (2)

[Claims] In a PWM converter that obtains a direct current from a multi-phase alternating current, a command value of a direct-current voltage to be controlled is a value obtained by multiplying a peak value of a line voltage of the multi-phase alternating current by a predetermined coefficient. A control device for a PWM converter for obtaining DC from a polyphase AC power supply. 2. A PWM converter for obtaining DC from polyphase alternating current, wherein a command value of a DC voltage to be controlled is obtained by multiplying a peak value of a line voltage of the polyphase alternating current by a predetermined coefficient,
A control device for a PWM converter that obtains a direct current from a multi-phase alternating current power supply, wherein the control device is configured to select a higher one of a predetermined value and another predetermined value.