2 Contactors Distribution in EVs and HEVs

The battery and the traction inverter are electrically isolated by main contactors when the vehicle is switched off for safety reasons. The main positive contactor is between the positive battery pole and the traction inverter while the main negative contactor is between the negative battery pole and the traction inverter. Both these contactors are required for safety robustness. The pre-charge contactor with a series current-limiting resistor is in parallel with the main positive contactor and used to charge the initially discharged DC link capacitor before closing the main contactors to avoid the high inrush current which might damage the battery, power contactors, and DC link capacitor. The two main contactors and one pre-charge contactor comprise an indispensable configuration for full HEVs.

In plug-in HEVs, a pair of additional AC charge contactors is inserted to establish a connection between the traction battery and the onboard charger. The onboard charger of the vehicle gets power from an AC charger, converts that AC power to DC to charge the battery.

For battery EVs, another pair of DC fast charge contactors is inserted to establish a connection between the traction battery and the DC fast-charge equipment. The DC fast charging is essential for long distance driving and large battery EV fleets. An auxiliary contactor like the electric heater for the passenger compartment is mandatory because there is no waste heat available from a combustion engine.

Main contactors, pre-charge contactors, and DC charge contactors are mostly located in the battery junction box (or battery disconnect unit). AC charge contactors are likely to be placed in the battery power distribution unit which is adjacent to the onboard charger.