Consequences of internal short-circuits in very high power converters

As a rule, very high power converters are custom designed. One of the most important problems is a phenomenon of high current flow during internal short circuits caused by semiconductor device breakdown. This situation may result in device package explosion and other damage caused by the destructive action of electrodynamic forces. The proposal of fast fuses elimination, commonly used as short-circuit protection, requires the determination of device explosion strength characteristics (peak value of case destroying current vs. time). Then it is necessary to design such a level of the converter load that the device current will not exceed the admissible value before the tripping of the AC supply circuit-breaker. In the paper, overcurrent protection methods are analysed. Some experiences and test results in this field are given. The mechanisms of destruction of power semiconductor devices caused by very high short-circuit currents are discussed. In conclusion, guidelines for the design of power electronic equipment without fast semiconductor fuse overcurrent protection are given.