JPH0757103B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Use of the Invention] The present invention relates to a power conversion device having an inverse converter, which has a DC reactor and bridges elements (transistors and GTOs) having a self-turn-off capability. In particular, the present invention relates to a circuit structure suitable for protecting main circuit elements.

[Background of the Invention]

Fig. 1 shows the main circuit of a power conversion device composed of a power transistor (hereinafter abbreviated as TR) and a gate turn-off thyristor (hereinafter abbreviated as GTO) that are elements capable of self-turn-off. In this figure, an AC power supply 1 is connected to an input terminal of a forward converter 2, and a DC output of the forward converter 2 is supplied to an inverse converter 4 via a DC reactor 3. There is. The inverse converter 4 is a three-phase bridge connection, and each arm is formed of GTO 41 to 46 and diodes D41 to D46 connected in series. In this circuit configuration, in order to protect the main circuit elements 41 to 46 in case of power failure such as power failure, momentary power failure, undervoltage, etc.
Or, you have to turn off the base signal of GTO (hereinafter referred to as GTO as a representative), but if you turn it off immediately,
Energy stored in the inductance of the DC reactor 3 causes an overvoltage. Therefore, conventionally, at least one of the upper arm and the lower arm of the inverse converter 4 is simultaneously ignited for the purpose of circulating the energy by short-circuiting the P-N which is a DC output for a certain time until the energy of the reactor 3 is discharged. It was short-circuited. However, since GTO and TR have self-extinguishing ability, they cannot maintain the conduction state unless the base current continues to flow, and if the base current becomes insufficient, the element will be thermally destroyed. Therefore, until the stored energy of the DC reactor is released, it is necessary to supply power to keep the base current, which causes a problem that the device becomes large and expensive.

Incidentally, FIG. 2 shows the voltage and current waveforms on the power supply side when the inverse converter is composed of a switching element having a turn-off capability.
FIG. 3 shows the voltage and current waveforms on the motor 5 side. FIG. 4 and FIG. 5 respectively show a second circuit of the circuit in which the thyristor constitutes the inverse converter without using the element having the self-turn-off capability.
Current and voltage waveforms corresponding to Figures and 3 are shown. When using an element with self-turn-off capability,
It can be seen that the waveform supplied to the motor is more sinusoidal and excellent.

The switches connected in parallel to the DC reactor are shown in Japanese Examined Patent Publication Nos. 52-25532 and 52-25535, but these circuits have a self-turn-off capability as the main switching element. No thyristor is used and no disclosure is made as to when the switch opening / closing operation is performed.

[Object of the Invention]

An object of the present invention is to provide an inexpensive protection device which is an element having a self-turn-off capability and which is provided when a power supply is abnormal when a power conversion device is configured.

The power failure is, for example, a power failure, a momentary power failure, an undervoltage, or when the upper power supply of the device is turned off or off.

[Outline of Invention]

The power converter of the present invention is configured by connecting a forward converter for converting AC power to DC power and an element having a self-turn-off capability to a bridge, and receiving the output of the forward converter to convert this to AC power. A reverse converter for converting into a reverse converter and a direct current reactor connected between the reverse converter and the forward converter, wherein a voltage for detecting a decrease in voltage on the input side or the output side of the forward converter It is characterized in that it has a detecting means and a switch which is connected in parallel to the DC reactor and is closed when the voltage detecting means detects a decrease in the voltage.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. 1 is a 3-phase AC power supply, 2 is a forward converter for converting AC to DC, 61
Is a thyristor as a switch provided according to the present invention,
3 is a DC reactor, 4 is an inverse converter, and each arm is configured by connecting a GTO and a diode in series.
Reference numeral 5 is a three-phase induction motor. This circuit configuration is based on the forward converter 2
The output of the three-phase AC power supply 1 to DC, and the DC output smoothed by the DC reactor 3 is again converted to 3 by the inverse converter 4.
It is converted into a phase alternating current and supplied to the three-phase induction motor 5. Reference numeral 90 denotes these control circuits, 51 denotes a current feed back, and 81 denotes a voltage feed back. Reference numerals 91 and 92 denote gate circuits. In such a circuit configuration, the voltage detection means 53 through the transformer 52 that supplies power to the 90 detects an abnormality in the power supply (power interruption, momentary power failure, undervoltage, etc.) and, at the same time, the GTO4
Signals 101 and 102 for turning off the GTO forming the forward converter 2 and the inverse converter 4 and a signal 100 for turning on the switch 61 are generated from 53 within an allowable time in which the base currents of 1 to 46 are not insufficient. Signal to turn on thyristor 61, and signals 101 and 102
As a result, the forward converter 2 and the inverse converter 4 are suddenly protected by the base stop. This is because the energy of the DC reactor 3 is circulated through the thyristor 61 when the thyristor 61 is turned on,
This is because the occurrence of overvoltage is suppressed. Reference numeral 54 indicates an overvoltage detection circuit during normal operation. Reference numeral 82 is a voltage detection signal for forming an AVR system. 110 is an OR circuit.

The switch 61 may be a non-contact switching element having no self-turn-off capability or a contact switch. However, it is desirable to use a contactless switch that does not have the ability to self turn off. A resistor may be connected in series to the switch. The voltage detecting means may be configured to detect that the input voltage of the voltage detecting means has dropped below a certain value, or it may detect that the input voltage has dropped below a certain value. good.

〔The invention's effect〕

According to the present invention, when a reverse converter using a transistor or a GTO that is an element having a self-turn-off capability is configured, the power source of the device is a power failure, a momentary power failure, an undervoltage, or a contactor of a higher device. When the inductance energy of the DC reactor disappears when it is turned off, etc.
Since it is not necessary to hold the base signal of the element by a battery power supply or the like, the control current of the device can be greatly reduced in size and simplified, and an inexpensive power conversion device can be provided.

[Brief description of drawings]

FIG. 1 is a main circuit configuration diagram of a known power conversion device using a GTO element, and FIGS. 2 and 3 are voltages and currents on a power source side and a motor side when an element GTO having a self-turn-off capability is used. Waveforms, FIGS. 4 and 5 show the same waveforms when an element having no self-turn-off capability, for example, a thyristor is used. FIG. 6 is a circuit diagram showing an embodiment of the power converter of the present invention. Reference numeral 1 is a three-phase AC power source, 2 is a forward converter, 3 is a DC reactor, 4 is an inverse converter, 53 is a voltage detecting means, and 61 is a thyristor as a switch.

Claims (1)

[Claims] 1. A forward converter for converting AC power supplied from an AC power source into DC power and an element having self-turn-off capability are bridge-connected. A reverse converter that receives the output of the forward converter and converts the output to AC power, a DC reactor connected between the reverse converter and the forward converter, and the reverse converter. In a power conversion device comprising a three-phase induction motor connected to the output of the converter, a voltage detection means for detecting that the voltage on the input side or the output side of the forward converter has dropped below a predetermined constant value, and Switch means connected in parallel to the DC reactor, and a control circuit for generating a signal according to the output of the voltage detection means, and when the voltage detection means detects a decrease in the voltage, the control is performed. Times Power conversion apparatus characterized by being configured to supply an ON signal to said switching means simultaneously supplies a turn-off signal to each of the forward converter and the inverter from.