The problems of voltage notch phenomena in power AC/DC converters

In this paper, voltage notch have been analyzed based on theoretical equations at during commutation time of a AC/DC converter. Depth of voltage notch in the converter busbar, depend on several parameters: feeder system impedances (Xs), converter impedance that placed between feeder and converter (Xt) and fire angle of controllable converters (Figure 1). By the way, characteristics variation of notch depth and wide according to system impedances and DC current of converter load, are presented. Main matter of this paper, discuss about oscillation frequency of converter voltages during commutation time. These frequencies depend on system impedances size (Xs+Xt), capacitor banks in network and capacitors size of snubber circuits. In final conclusion experimental results that obtained from a controllable AC/DC converter have been compared with simulation and theoretical results.