Commutation phenomena in a static power convertor

A systematic experimental and theoretical study was made of the effect of various inherent and extraneous circuit parameters on the commutation oscillations and on the period of commutation overlap in a static power convertor. The initiation of oscillations by a voltage jump occurring across a convertor device at the start and at the end of commutation overlap was analysed for a variety of conditions, and the theoretical deductions were experimentally verified. The period of commutation overlap in a convertor without extraneous capacitances and in steady-state operation was shown to be determined by the sum of the instantaneous values of direct current prevailing at the start and the end of the overlap. Enforced reductions of the period of commutation overlap were found to be obtained by an appropriate adjustment of the magnitudes of the relevant parameters in a controlled-rectifier circuit either with capacitors connected between the anodes of the convertor devices or with capacitors connected between the input terminals of the convertor transformer in the presence of series inductances in the a.c. supply lines.