JPH07170759A - Detecting method of short circuit of bridge circuit in power converter - Google Patents

Abstract

PURPOSE:To realize the detection of the short circuit of a bridge circuit in a power converter through a simple detecting method. CONSTITUTION:In a power converter constituted by connecting a bridge circuit consisting of a capacitor 2 and two semiconductor switching elements 4 and 5 connected in series in parallel at both ends of a DC power supply 1, both end voltage of the arm of the bridge circuit is detected and compared with the reference value of a voltage frequency divider circuit 8 in a comparator circuit 9, thus detecting the drop of voltage with a short circuit. A drive signal to the semiconductor switching element 5 from a gate drive circuit 11 through an interrupting circuit 10 is interrupted by an output signal from the comparator circuit 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a short circuit in a bridge circuit in an inverter, a converter or the like which constitutes a power converter.

[0002]

2. Description of the Related Art A short circuit between upper and lower arms in a bridge circuit composed of semiconductor switching elements has been detected by the method shown in FIG. In FIG. 3, a diode 107 is provided between a negative terminal of a capacitor 102 connected in parallel to both ends of a DC power supply 101 and an emitter terminal of a semiconductor switching element 105 in a bridge circuit composed of two semiconductor switching elements 104 and 105 connected in series. Is inserted in advance, and a circuit including the Hall CT 103 connected in series with the resistor 106 in parallel with the diode 107 is provided. When the semiconductor switching elements 104 and 105 are turned on at the same time, a short-circuit accident occurs between the upper and lower arms, so that a short-circuit current is supplied from the DC power supply 101. This short circuit current is detected by Hall CT103,
The detection voltage converted through the hole CT 103 is compared with the reference voltage 108 in the comparison circuit 109 to detect the occurrence of a short circuit accident. The detection signal from the comparison circuit 109 is input to the cutoff circuit 110, and the drive signal output from the gate drive circuit 111 that controls ON / OFF of the semiconductor switching elements 104 and 105 is output by the command signal from the cutoff circuit 110 to the semiconductor switching element 104, 1
05 was blocked at the same time or one of them was blocked.

[0003]

In the above-described method for detecting a short-circuit current in which the hole CT is inserted, the power source impedance is large due to the hole CT 103, the resistor 106, the diode 107, and the wiring connecting these components, which constitute the detection circuit. Therefore, the snubber loss of the semiconductor switching element also increases. Further, although electrostatic noise is likely to occur in the inverter input section, the Hall CT 103 has a drawback that it is weak against electrostatic noise. Therefore, it is not appropriate to use the Hall CT for detecting the short circuit current of the bridge circuit which constitutes the inverter. As a means for detecting the short-circuit current, there is a method of detecting the discharge current of the capacitor by AC CT, but there is a drawback that the configuration of the detection circuit becomes complicated. The present invention has been made in order to solve the above-mentioned drawbacks of the prior art, and provides a method for detecting a short circuit voltage by detecting the voltage across the arm of a bridge circuit and comparing the voltage drop across the arm with a reference value. It is a proposal.

[0004]

In order to achieve the above-mentioned object, a method of detecting a short circuit of a bridge circuit in a power conversion circuit according to the present invention detects a voltage at both ends of an arm of the bridge circuit and detects both ends due to the short circuit. A short circuit is detected by comparing the amount of voltage drop with a reference voltage.

[0005]

When the voltage across the arms of the bridge circuit is detected, the voltage drops by 0.5E _DC (E _DC is the DC power supply voltage) or more in the case of an arm short circuit, so that the short circuit can be detected by comparing with the reference voltage.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment according to the present invention, in which a DC power supply 1 is connected at both ends thereof in parallel with a bridge circuit constituted by connecting a capacitor 2 and two semiconductor switching elements 4 and 5 in series. The voltage across the bridge circuit is detected by the detection circuit 14. The drop of the voltage across the parallel capacitor 2 when a short-circuit current flows is about 0.1E _DC when the DC power supply voltage is E _DC as shown in FIG. 2A, but the voltage across the arm of the bridge circuit is 2E is about 0.5E _DC even when the wiring inductance is as small as 70 nH, and becomes 0.5E _DC or more when the wiring inductance is 70 nH or more, as shown in FIG. 2B. That is, even if the inductance of the wiring is large, the voltage drop across the arm is expected to be 0.5E _DC when a short circuit occurs, so it is easy to detect a short circuit, and the gate drive is performed via the comparison circuit 9 and the cutoff circuit 10. The drive signal of the circuit 11 is cut off.

Next, details of the short circuit detection circuit and the cutoff circuit of the semiconductor switching element will be described. In FIG. 1, the voltage across the arms of the bridge circuit is input to the comparison circuit 9 via the detection circuit 14 and to the comparison circuit 9 via the average value voltage detection circuit 13 and the voltage divider circuit 8. The DC power supply voltage E _DC is averaged by the average value voltage detection circuit 13, and further divided by the voltage division circuit 8 to become the reference voltage of the comparison circuit 9. For example, if the voltage divider circuit 8 is divided by 1/2, the voltage of 1/2 of the DC power supply voltage E _DC becomes the reference value, so that the voltage across the arms of the bridge circuit when a short-circuit current flows When is less than 0.5E _{DC, the} occurrence of short circuit is detected.
The frequency division ratio of the voltage divider circuit 8 is adjusted according to the circuit characteristics so that the occurrence of short circuit can be detected accurately.

When a short circuit is detected in the comparison circuit 9, the drive signal from the gate drive circuit 11 to the semiconductor switching element 5 is cut off by the cutoff circuit 10 by the output signal from the comparison circuit 9 to the cutoff circuit 10, and semiconductor switching is performed. The element 5 is turned off. The semiconductor switching element 4 is configured to be on / off controlled by the gate drive circuit 11 without the interruption circuit 10.

[0009]

As described above, the method for detecting a short circuit in the bridge circuit in the power converter according to the present invention detects the voltage across the arms of the bridge circuit and detects the occurrence of a short circuit by the amount of drop in the detected voltage. To do. Therefore, the size of the detection device is smaller than that of the short-circuit detection method using the Hall CT, and the inductance of the wiring can be reduced, so snubber loss is also reduced. Further, unlike the Hall CT, troubles due to electrostatic noise do not occur, and an economically excellent short-circuit current detection method with less conversion loss can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a short circuit detection method according to the present invention.

FIG. 2 is a voltage waveform diagram when a short circuit occurs.

FIG. 3 is a block diagram showing a conventional short circuit detection method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Capacitors 4, 5 Semiconductor switching element 8 Voltage divider circuit 9 Comparison circuit 10 Breaking circuit 11 Gate drive circuit 13 Average value voltage detection circuit 14 Detection circuit

Claims (1)

[Claims] 1. A bridge circuit in a power conversion device comprising two semiconductor switching elements connected in series, wherein the voltages across the two semiconductor switching elements forming the arm of the bridge circuit are detected and input to a comparison circuit. A short circuit detection method for a bridge circuit in a power conversion device, comprising detecting a short circuit in the bridge circuit by comparing a drop amount of the voltage across both ends with a reference voltage in a comparison circuit.