A Novel Welding Monitoring and Detection Strategy for High Voltage Contactors in Electric Vehicles 2021-26-0166

DC fast charging brought a paradigm shift in EV & HEV battery charging with reduced charging times. The high voltage contactors are the major components in the DC fast charge controller and provide reliable and fast switching of DC power from EVSE to battery. However, unstable voltages, high inrush currents, poorly designed surge protectors, end of electrical endurance lifetime etc. cause welding of contactors while operating with high voltages. In general, welding detection algorithms, the voltages across contactors are compared. Current welding strategy has limitations as it does not detect high voltage contactor welding during charging, initiates power shut off, safe state is not reached and welding factor not used for contactor lifetime calculation. This paper proposes a novel strategy to monitor and detect welding using contact resistances and lifetime counters to detect and report welding even before the contactors are normally triggered to open. The safe state is ensured and DC power transfer is shut down before contactor open triggers. The work focuses on continuously monitoring contactor resistance for not welded, partially welded and welded conditions and use resistance measurements to calculate contactor life time data with additional factor of wear and tear obtained from resistance measurements. This is advantageous to EVs as partial welding and welding probabilities are predicted in this strategy. The lifetime prediction algorithm is combined with welding so as to get more accuracy.