A Novel Full-Speed Sensorless Control Strategy Based on Electric Vehicle PMSM

In view of the unsteady transition between the high-speed and low-speed sensorless control strategies in the full speed range of the Electric Vehicle (EV) permanent magnet synchronous motor (PMSM), the sectional current reduction rate (SCRR) method and the direct switching method (DSM) are proposed to achieve the smooth transitions in the starting and braking process, respectively. To start with, the I/F control method is adopted to realize the startup successfully. And then in order to offer a smooth transition from I/F control method to Sliding Mode Observer (SMO) control mode, the given rotor current is reduced by SCRR, at the same time the synchronous rotating reference frame is close to the real rotor reference frame gradually. When the frames coincide with each other as far as possible, the two control methods complete the switching. In the braking state, the motor would be controlled by DSM, which switches the control method from the SMO to I/F method, to ensure the ride comfort of EV. Finally, the simulation not only verifies the feasibility of SCRR and DSM, but also compares the SCRR method with DSM to the traditional one-section current reduction rate method (OSCRR) without DSM. The results show that comparing with the traditional OSCRR, SCRR can accelerate the starting switching process of the motor and ensure a smooth and no-impact procedure. In addition, chatter in the braking state is eliminated effectively by DSM and the system has good anti-load-disturbance, dynamic and static response capability in various applications.