4.7. Commutation Overlap Phenomenon of Diodes

Fig. 4.24(a) shows a power circuit of a three-phase half-bridge rectifier which will be used to explain the commutation overlap phenomenon of the diodes. The commutation overlap is the undesired simultaneous conduction of two diodes which leads to a short circuit between any two input ac phases. This phenomenon is caused by the input source inductances which affect the increase and decrease rate of rise of the current flowing through each diode when switching between forward- and reverse-biased states. This short-circuit phenomenon, shown in Fig. 4.24(a), is called commutation overlap phenomenon. For example, let's assume that diode D1 is conducting supplying the load with a pure dc current of I¯

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