Endurance test circuit for power capacitors

Power capacitors used in high-power circuits like GTO turn-off snubbers need severe endurance tests to ensure their reliability in today's very demanding applications. A special test circuit has been developed and built in order to apply to the capacitors the voltage and current waveforms that are required to reproduce its real operating conditions. It consists essentially of a full bridge circuit, made by many IGBT modules in series/parallel connection: the capacitor under test is connected to the AC side, through a series inductor, and a DC power supply is connected to the DC side of the bridge. Each of the four IGBT switches that form the bridge is divided into two blocks that can be series or parallel connected, in order to accommodate a broad range of operating voltage and current for the capacitor under test.