Electric Propulsion Systems

Electric propulsion systems are at the heart of EVs and HEVs. They consist of electric motors, power converters, and electronic controllers. The electric motor converts the electric energy into mechanical energy to propel the vehicle or vice versa, to enable regenerative braking and/or to generate electricity for the purpose of charging the on-board energy storage. The power converter is used to supply the electric motor with proper voltage and current. The electronic controller commands the power converter by providing control signals to it, and then controls the operation of the electric motor to produce proper torque and speed, according to the command from the driver. The electronic controller can be further divided into three functional units—sensor, interface circuitry, and processor. The sensor is used to translate the measurable quantities, such as current, voltage, temperature, speed, torque, and flux, into electric signals through the interface circuitry. These signals are conditioned to the appropriate level before being fed into the processor. The processor output signals are usually amplified via the interface circuitry to drive power semiconductor devices of the power converter. The functional block diagram of an electric propulsion system is illustrated in Figure 6.1.