Improved High current source of Synthetic Test Circuit for HVDC thyristor valve

Synthetic Test Circuit (STC) system for thyristor valve of current-type High Voltage Direct Current (HVDC) typically consists of a low-voltage high-current and a high-voltage low-current source. In order to provide the isolation between each source, auxiliary valve should be inserted, and its voltage and current ratings are greater or equal to those of the test thyristor valve. To ensure the turnoff of that auxiliary valve additional voltage source is necessary to apply reverse voltage to the auxiliary valve at turn-off instant. This paper describes a new high-current source to minimize turn-off time of the auxiliary valve. The proposed system consists of two chopper, auxiliary valve, auxiliary IGBT, diode, resistor, and capacitor. Computer simulation and experimental results show the validity of the proposed scheme.