JPH0256032B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection circuit for power semiconductor switch devices.

Power semiconductor switch devices, such as thyristors, are equipped with a so-called snubber circuit in which an overvoltage absorbing capacitor is placed in parallel with the device in order to suppress the rate of increase in the voltage between the main terminals (dv/dt) to a predetermined value or less when the device is turned off. . In particular, power gate turn-off (GTO) thyristors, which have recently been put into practical use, have a fast turn-off speed, so they often fail due to a steep voltage rise rate. I had a problem that required a limiting resistor.

Figure 1 shows a three-phase control circuit with a GTO thyristor as the main switch element.
TH _U , TH _V , TH _W , T _Y , and TH _Z are provided with a snubber circuit SN consisting of a series circuit of a diode D ₁ and a capacitor C ₁ and a discharge current limiting resistor R ₁ in parallel with the diode D ₁ . Here, the resistor _R1 limits the discharge current within a range that does not exceed the switching capability of the thyristor in order to discharge the capacitor _C1 when the thyristor is turned on. This resistance
R ₁ is, for example, use 2 μF for capacitor C ₁ ,
When operated with a DC voltage of 600V and a repetition rate of 1KHz, the resistance loss per wire is approximately 360 Watts, resulting in problems such as increased size, power consumption, and increased cooling capacity.

SUMMARY OF THE INVENTION An object of the present invention is to provide a protection circuit which eliminates the conventional problems by regenerating the energy of an overvoltage absorbing capacitor to the DC power supply side and thereby omitting a discharge current limiting resistor.

FIG. 2 is a circuit diagram showing one embodiment of the present invention, and shows one phase. As a main switch element
GTO thyristors TH _U and TH _X each have diodes.
A series circuit of D ₁ and overvoltage absorbing capacitor C ₁ is connected in parallel, and each capacitor C ₁ has a transistor as a semiconductor switch for chopping control.
The series circuit of TR and reactor transformer T is connected in parallel. The secondary winding outputs of the reactor transformer T are each connected in series to a rectifier diode D ₂ and connected between DC power lines P and N.

Transistor TR is GTO as shown in Figure 3.
During the ON period of the thyristor TH _U or TH _V , stepping control is performed at a constant cycle (high frequency), and when the thyristor is ON, the energy stored in the capacitor C ₁ is taken in as the primary input current i T of the reactor transformer T, and the energy of the transistor TR is taken in as the primary input current i _T of the reactor transformer T. When off, the rectified current i _d is regenerated from the secondary winding through diode D ₂ to the DC power supply. With this chopping control, the energy of capacitor C ₁ is transferred to GTO thyristor TH _U ,
During each ON period of _THL , the voltage V _C is completely regenerated to the DC power supply and returned to the discharge state, and the overvoltage can be absorbed the next time the thyristor is turned off. Chopping control of transistor TR is GTO
Gate control circuit GC for thyristors TH _U , TH _X , etc.
synchronously controlled by the gate control signal.

Note that the transistor TR, transformer T, and diode D ₂ are integrated into a module circuit with a diode D ₁ and a capacitor C ₁ , as well as a transistor.
Making it a modular circuit that includes the TR's chopping control circuit makes it easier to handle.

As described above, the protection circuit according to the present invention has a high power capacity that limits the discharge current from the capacitor because it regenerates the energy of the overvoltage absorption capacitor to the DC power supply side through DC-DC conversion instead of discharging it to the main switch side. This eliminates the need for a resistor, making it possible to downsize the device, and solving problems of power loss and heat dissipation. Furthermore, since the discharge current from the capacitor that flows when the main switch is initially turned on is eliminated, the switching loss in the main switch when it is turned on can be significantly reduced.

In addition, since the energy of the capacitor is regenerated into the power supply and power efficiency is improved, the capacitance of the capacitor can be designed to be large, so the turn-off current (current that can be turned off by the gate) of the GTO thyristor as the main switch is large. Therefore, the GTO thyristor can be used effectively. Furthermore, since the main switch is not included in the discharge path of the capacitor, loss in the main switch due to the discharge current can be eliminated. In addition, since the capacitor discharges are stepped by stepping, the stepping frequency can be increased to reduce the size of the transformer.

[Brief explanation of the drawing]

FIG. 1 is a protection circuit diagram of a conventional power semiconductor switch element, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is an operation waveform diagram of FIG. 2. _{TH U} , _TH
D ₂ ... Rectifier diode, GC... Gate control circuit.

Claims (1)

[Scope of Claims] 1. In an overvoltage absorption circuit for suppressing a voltage rise rate at turn-off of a power semiconductor switch element controlled on and off by a gate control circuit to within a predetermined range, the power semiconductor switch element A series circuit of a diode and an overvoltage absorbing capacitor connected in parallel to the element, a series circuit of a chopping control semiconductor switch and a primary coil of a reactor transformer connected in parallel to the overvoltage absorbing capacitor, and a secondary output of the reactor transformer. A series circuit of the secondary coil of the reactor transformer and a rectifying diode for regenerating the DC power supply is connected between the positive and negative poles of the DC power supply, and the switching control semiconductor is connected during the ON period of the power semiconductor switch element. 1. A protection circuit for a power semiconductor switch element, characterized in that energy stored in the overvoltage absorbing capacitor is regenerated into a DC power source by controlling the switch in a stepping manner by the gate control circuit.