Protection Analysis Of AC - DC Converter With Low - Voltage Fuse

1. Protection required by converter

Converters (such as rectifiers, inverters, frequency conversion equipment, etc.) are usually composed of multiple power electronic components. The ideal protection equipment should ensure that the following conditions are met: once the semiconductor equipment fails, the circuit should be disconnected as soon as possible to prevent other equipment from being damaged (experience shows that in this regard, the semiconductor fails due to short circuit and leads to high current). For other faults in the equipment, it is recommended to disconnect the circuit before damaging the semiconductor equipment. Before damaging semiconductor equipment, it is recommended to cut off the overcurrent that may cause damage.

2. Low voltage fuse for semiconductor protection

The fuse for semiconductor protection complies with gb/t13539.4 (iec60269-4) "Supplementary requirements for fuse links for the protection of low voltage fuses for semiconductor equipment". Through the narrow diameter design of the melt, it runs faster than other protective appliances under the specified current. At the same time, by selecting and grinding the arc extinguishing filler, the open circuit overvoltage during arc extinguishing can be reduced to a very low level. Therefore, the action of the semiconductor fuse can not only quickly disconnect the fault current, but also should not cause unacceptable Overvoltage on any semiconductor equipment. In short, Semiconductor Fuses should meet the following requirements:

(1) Fast;

(2) The allowable passing energy of overcurrent is small;

(3) Large carrying capacity;

(4) Low power consumption;

(5) The breaking voltage is moderate.

Gb/t13539.4 (iec60269-4) "Supplementary requirements for fuses for low voltage fuse protection of semiconductor equipment" defines two application categories of semiconductor equipment characteristics according to the disconnection range, R and s:

(1) Compared with S-type, R-type moves faster, and the allowable energy i2t of overcurrent is smaller;

(1) Compared with the R-type, the S-type has lower power consumption.

If the equipment fails, the fault current flowing through the semiconductor device needs to be interrupted before causing damage to the device. In order to achieve this, the allowable conduction energy i2t of the fault current of the fuse needs to be less than the allowable limit value of the protected semiconductor. The allowable energy value of operation (operation i2t: the sum of energy of pre arc time and arc starting time) depends on the recovery voltage. The corresponding curve is provided by the fuse manufacturer.

The breaking voltage of the low-voltage fuse during operation shall not exceed the withstand voltage of the semiconductor pn junction. According to the manufacturer's data, the switching voltage (fuse working voltage) can also be reduced when the recovery voltage is lower than the rated voltage of the fuse. The working current, possible fault current and recovery voltage depend on the position and working mode of the fuse installed in the converter circuit.

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