JPH0732530B2 - Short-circuit protection method for power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a gate turn-off thyristor (simply a GTO
Also abbreviated. Short circuit protection method in a power converter using a power semiconductor element capable of self-extinguishing.

[Conventional technology]

Generally, the maximum controllable current value is specified for the self-extinguishing type power semiconductor element such as GTO, and it is known that if the element exceeds or exceeds this value, the current is cut off or destroyed. Therefore, various protection methods have been conventionally proposed.

FIG. 4 is a block diagram showing a conventional example of a protection system. In the figure, 1 is a DC power supply, 2 is an overcurrent protection device such as fuse, 3 is a filter reactor, 4 is a filter capacitor, 5 is a freewheeling diode, 6 is a current limiting reactor, 7 is a damping resistor, and G1 to G6 are Gate turn-off thyristors, D1 to D6
Is a diode, which constitutes a well-known inverter device. In addition, limit reactor 6
Is added in order to suppress the peak value of the short-circuit current and the current increase rate (di / dt) at the time of arm short circuit and load short circuit in the inverter bridge part. Further, 12 is a short-circuit monitoring circuit, 13 is a gate control circuit, and 14 is a gate drive circuit. When the arm is short-circuited, these circuits operate to protect the GTO. In addition, 10 is a load.

Now, for some reason, the gate turn-off thyristor G
When 1 and G2 arm short-circuit, capacitor 4 → reactor 6
→ Short-circuit oscillating current flows through the route of G1 → G2. The oscillating current at this time is expressed by the following equation and is superimposed on the load current. However, here, the attenuation due to resistance is ignored.

Where C is the capacitance value of the filter capacitor 4, L is the inductance value of the limiting reactor 6, E is the voltage of the filter capacitor 4, and ω is the angular frequency. Is.

As a semiconductor (GTO) protection method against this arm short circuit accident, the following methods have been mainly used conventionally.

(B) Insert a limiting reactor with a large inductance to prevent the breaking current from exceeding the controllable current di / dt.
The method of suppressing the accident current and protecting against the accident current by GTO itself.

(B) A method of cutting off the accident current with another protective device so that the GTO does not cut or cut off the accident current.

The operation in each case will be described below.

(A) Protection method Fig. 5 shows the GTO current waveform when arm short circuit protection is performed.

Where t ₁ is the time from when the short-circuit current exceeds the detection level I _S until the detection signal is output, t ₂ is the time from when the detection signal is output to when the gate-off signal is output to the GTO, and t ₃ is the gate-off signal. Time from output to when GTO actually turns off current (G
Storage time of TO). That is, when the arm short circuit during inverter operation occurs, a current with a slope of approximately di / dt = E / L from the load current I _L is increased, the t ₁ + t ₂ hours after the current exceeds the detection level I _S , The gate-off current begins to flow in the gate of GTO. Although the GTO turns on and off the current after t ₃ after the off-current flows in the gate of the GTO, the GTO is not destroyed if this current value is less than the controllable current I _ATO . The inductance value required in this case is determined by the following equation so that I _OFF I _ATO .

Here, E _max represents the maximum value of the fluctuation range of the input voltage E.

(B) Protection method Figure 6 shows the GTO current waveform during arm short circuit protection.

Here, t ₁ is the time from when the short-circuit current exceeds the detection level I _S to the output of the detection signal, and t ₂ is the time from the output of the detection signal to the GTO gate inhibition. That is, when an arm short circuit accident occurs, the load current I _{L is} almost di / dt = E.
When the current rises at the slope of / L and exceeds the detection level I _S , t ₁ +
gate-off prohibition command after t ₂ is out, since the later is not out gate-off signal, never GTO is to and disconnection,
The oscillating current shown in the equation (1) above flows into the GTO. At the same time when the arm short circuit is detected, the overcurrent protection device 2 shown in FIG. 4 operates to disconnect the device from the power supply and complete the protection. During this period, it is considered that the element can withstand the above-mentioned oscillating current and the current flowing from the power supply before the protection device 2 completes the current limiting operation. At this time, the required inductance value is It is expressed as. However, this inductance value may be selected relatively large in view of the above-mentioned element withstand capability.

[Problems to be solved by the invention]

In the above method (a), since the limiting reactor needs to have a large inductance value, not only the device becomes large and expensive, but also the damping resistor that consumes energy by this reactor becomes large and the loss is increased. There is a problem that the energy becomes large and the efficiency is lowered.

On the other hand, according to the method (b), the inductance value does not need to be increased so much and the above-mentioned problem does not occur. Therefore, in practice, this method is often used.

However, in the case of this method, there is a problem that the protection device 2 is operated when the current exceeds the detection level I _S under any circumstances. In other words, considering the case where the voltage fluctuation range is very large, such as in the case of train lines, when the power supply voltage is low and di / dt is small (hatched area in Fig. 6), even if the gate is turned off after the short circuit is detected. ,
Since the GTO current is less than I _{ATO, it} can be cut off, and in the case of a load short circuit, there is often an inductance component in the short circuit, and since di / dt is small, protection by gate off is possible in the same way. In other words, in the case of the method (b), even when the GTO can be protected by cutting it off, an excessive current is supplied to the GTO to operate the protection device.
When the number of accidents is increased by deteriorating the element and the protection device, there is a problem that the device reliability is lowered.

Therefore, it is an object of the present invention to provide a protection method capable of performing appropriate semiconductor protection according to the situation of a short circuit current at the time of a short circuit accident.

[Means for solving problems]

A voltage detector that detects the input voltage of a power conversion device that uses a self-extinguishing element, a current detector that detects the current that flows through the element, and the fact that an accident has occurred is detected by monitoring the current. Short circuit detection means, and the cutoff current of the element is calculated by a predetermined calculation formula based on the voltage and current detection values at the time of detecting the short circuit and the time from the detection of the current to the actual output of the gate-off signal. And a judgment means for comparing the calculation result with a controllable current value of the element to judge whether short-circuit current interruption is possible, and the judgment means is such that the interruption current is equal to or less than the controllable current value of the element. When it is determined that the current can be interrupted, a gate-off signal is output to interrupt the current in the element, and when the interrupt current is larger than the controllable current value of the element, it is determined to be interrupted, and the current is not interrupted in the element. The gate-off prohibition signal is output to.

[Action]

FIG. 1 is a main view that best represents the features of the present invention. As is apparent from the figure, the short circuit detecting means 91, the breaking current calculating means 92 and the breaking judgment means 93 are provided, and the other parts are the same as in FIG.
However, the bridge inverter section (G1 to G6, D1 to D6)
For simplification, reference numeral 8 is shown in the figure.

The short-circuit detection means 91 monitors the output from the current detector 11, detects that a short-circuit accident has occurred when this exceeds a predetermined overcurrent detection level I _S , and outputs a predetermined detection signal. Upon receiving this detection signal, the breaking current calculating means 92 calculates the breaking current I _OFF represented by the following equation.

I _OFF = I _S + (E / L) × (t ₁ + t ₂ + t ₃ ) (4) where I _S is the overcurrent detection level, E is the input voltage (filter capacitor voltage), and L is the limiting reactor inductance. Value, t ₁ is the time from when the short-circuit current exceeds the detection level I _S to when the short-circuit is detected, t ₂ is the time from when the short-circuit is detected to when the gate-off signal is output to GTO, and t ₃ is the GTO storage time. ing.

In the above equation (4), L, t ₁ , t ₂ , and t ₃ are known, and the input voltage E is obtained via the voltage detector 15 which detects the capacitor voltage. The overcurrent detection level I _S can be obtained via the current detector 11 or a preset value can be used. In this way, I obtained by the disconnection current calculation means 92
_{When the power is OFF} , the GTO controllable current I
_It is compared with _ATO. If I _OFF I _ATO , the gate-off signal is output, and if I _OFF > I _ATO , the gate-off prohibition signal is output.

〔Example〕

FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a flow chart for explaining the operation of the processing apparatus.

In FIG. 2, reference numeral 97 is a processing device such as a micro computer, which is basically composed of a central processing unit CPU, a read only memory ROM, a random access memory RAM and the like. A program for controlling the CPU is written in the ROM, and the CPU takes in external data required from the input port 96 according to this program,
Alternatively, the arithmetic processing is performed while exchanging data with the RAM. Reference numerals 94 and 95 are A / D converters for performing analog-digital conversion on the analog signals from the current detector 11 and the voltage detector 15.

The operation will now be described with reference to FIG.

When the program starts, the processor 97 reads (see) the current value I from the A / D converter 94, and this value and the preset overcurrent detection level I _S
Comparing the door (see), read I <I _S If again the current value, the same operation is repeated until the II _S. When the short circuit becomes a happening II _S, processor 97 it bracts port 96
To the voltage detection value E through the A / D converter 95 (reference) and expressed by the equation (4) using I _S , L, t ₁ , t ₂ and t ₃ preset on the program. Calculate the current I _OFF that is applied (see). In the processing unit 97, this calculation result I _OFF is compared with the controllable current value I _ATO set by the program (see), and if I _OFF I _ATO , a gate-off signal, and if I _OFF > I _ATO , a gate-off prohibition signal. Are output to the output port 98 (see,). The output port 98 outputs a gate-off command to A ₁ when the input is a gate-off signal, and outputs a gate-off prohibition command to A ₂ when the input is a gate-off prohibition signal, which is supplied to the bridge inverter unit 8 through the gate control circuit 13.
Given to the GTO.

As described above, in the event of a short-circuit accident, the GTO's stroke and disconnection current are immediately calculated, and it is judged whether or not it can be disconnected.
The gate is turned off to protect the device, and when it is not possible, the gate off of the GTO is prohibited to prevent the device from being destroyed by cutting off or cutting off the current above the controllable current. Optimum protection according to the situation is possible.

In the above description, the short-circuit detecting means detects a short circuit when the overcurrent level is exceeded.
It is also possible to adopt a short circuit detection method by detecting the level of di / dt. The present invention can also be applied to self-turn-off devices other than GTO thyristors.

〔The invention's effect〕

According to the present invention, when the short circuit accident occurs, the semiconductor device breaks or breaks current is calculated, and if the current is less than the controllable current, the breakage current of the GTO is cut off or cut off by itself, so that the GTO's breakage or breaking ability is fully utilized. Since protection is possible, the overcurrent protection device is operated unnecessarily every time a short-circuit accident occurs, degrading the protection device, or a large surge current is passed through the semiconductor to shorten the device life. There are advantages that can be prevented.

[Brief description of drawings]

FIG. 1 is a main view which best shows the features of the present invention, and FIG.
FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a second diagram.
FIG. 4 is a flow chart for explaining the operation of the processing device in the figure, FIG. 4 is a configuration diagram showing a conventional example of a power conversion device protection system, and FIG. 5 is a reference diagram for explaining an example of the protection operation in FIG. , FIG. 6 is a reference diagram for explaining another example of the protection operation in FIG. Symbol description 1 ... DC power supply, 2 ... Overcurrent protection device, 3 ... Filter reactor, 4 ... Filter capacitor, 5 ... Reflux diode, 6 ... Limiting reactor, 7 ... Damping resistance,
8 ... Bridge inverter, 10 ... Load, 11 ... Current detector, 12 ... Short circuit monitoring circuit, 13 ... Gate control circuit,
14 ... Gate drive circuit, 15 ... Voltage detector, 91 ... Short-circuit detection means, 92 ... Disconnection / disconnection current calculation means, 93 ... Disconnection / disconnection determination means, 94,95 ... A / D converter , 96 …… input port, 97 …… processing unit, 98 …… output port, G1 to G6 …… gate turn-off thyristor (GTO), D
1 to D6 ... Diode, CPU ... Central processing unit, ROM ... Read-only memory, RAM ... Random access memory.

Claims (1)

[Claims] 1. A voltage detector that detects an input voltage of a power conversion device that uses a self-extinguishing element, a current detector that detects a current flowing through the element, and an accident occurs by monitoring the current. A short-circuit detecting means for detecting the fact that the voltage and current are detected at the time of detecting the short-circuit, and the element is calculated by a predetermined arithmetic expression based on the time from the detection of the current to the actual output of the gate-off signal. And a determination means for comparing the calculation result with the controllable current value of the element to determine whether or not the short-circuit current can be interrupted. When it is below the control current value, it is determined that the device can be interrupted, and a gate-off signal is output in order to interrupt the current in the element. Then Den Short-circuit protection method in a power conversion apparatus characterized by generating a gate inhibit signal so as not to block.