Seamless Transition to Sensorless Control of EV Traction IPM Motors Using Virtual High-Frequency Voltage Injection

Due to the possible malfunction or failure of the position sensor mounted on an electrical vehicle (EV) traction motor, a backup position sensorless torque control strategy is required. The switching-on-the-fly seamless transition from sensored mode to sensorless mode is particularly challenging at low-speed operation, where high-frequency injection (HFI) is usually employed to estimate the rotor position and speed through a tracking observer that must be properly initialized. Therefore, this paper proposes a virtual high-frequency voltage injection technique that is able to achieve a seamless transition between sensored mode and sensorless mode for interior permanent magnet (IPM) motors in EV traction drives. Detailed experimental validation is provided for a 157kW EV traction IPM motor mounted on a test rig.