Research on dynamic modeling and transient characteristics of hybrid DC switch

DC contactor is one of the key equipment in DC rail traction system. This paper proposes a 2 kV hybrid DC contactor based on natural current transfer. The topology consists of mechanical switch, solid-state switch, passive RCD circuits for snubber and dynamic voltage balancing, and MOV for absorption. Transient characteristics of current transfer, snubber and absorption are studied by theoretical analysis. The dynamic model of hybrid DC contactor is built and impact of model parameters, including stray inductance, snubber capacitance and balancing circuit parameters are discussed in detail. Results show that small stray inductance ensures fast current transfer and large capacitance improves the reliability of IGBT and MOV. For series-connected IGBTs, consistency of snubber capacitances and turn-off trigger times should be improved. Verification experiments are carried out for control signal coordination, current transfer process, snubber and absorption process and series dynamic voltage balancing. As the indicator of electrical endurance, Arc energy of hybrid contactor is less than ten thousandth of the mechanical contactor, which indicates hybrid DC contactor has higher electrical endurance.