6 Summary

Contactors are widely used in EV and HEVs to connect and break power supply lines. The required current curve generated by the coil driving the circuit is mandatory to ensure proper operation of the contactor. Attention should be paid to EMC issues due to high current and high frequency. In addition, smart contactors with special controls and diagnosis features are already used by some customers.

Meanwhile, there is a trend that solid-state switches replace electromechanical contactors for low noise, high reliability, and a long lifetime. In general, the contactors can fail by welding closed while the failure mode of solid-state switches is mostly open. However, there are also some drawbacks for the solid-state switches. The cost of solid-state switches is currently high and there is a fixed-value voltage drop on output due to internal impedance. Also, there is a leakage current even in OFF mode. That is why it is stipulated that at least one electromechanical contactor must be retained at a pole while a solid-state switch is used in the other pole.