Over Voltage Caused by Asynchronous Turn-on of Series Connected IGCTs in High Voltage MDCCB

High voltage mechanical dc circuit breaker (MDCCB) has been widely used in Voltage source converter based high-voltage dc transmission systems (VSC-HVDC). Series connected IGCTs are utilized in high voltage MDCCB to provide high blocking voltage. This paper analyzed the overvoltage problem during the turn-on process of series-connected snubberless IGCTs in high voltage MDCCB. First, a two-unit 2T- 3R model is developed to simulate the turn-on characteristics of series connected IGCTs without snubber and the effect of different gate delays on the anode voltage is analyzed. Then, a high-voltage DC circuit breaker circuit model is established using ideal switches to replace IGCTs and the influence of asynchronous turn-on on the overvoltage of submodules is analyzed. The results shows that more than 500 ns of turn-on time difference can cause voltage overshoot of IGCT devices. Several microseconds turn-on delay will cause significant over voltage on the latter turn-on sub-module.