Sensorless Control Strategy of the Wound Rotor Synchronous Machine for EV Powertrains

Electric vehicle manufacturers are increasingly adopting the non-rare-earth Wound Rotor Synchronous Machine (WRSM) due to its relatively low cost, wide speed range, and adjustable power factor. However, the operating conditions with torque disturbances and continuous speed variations present challenges to the robustness and dynamic performance of the powertrain control strategy while necessitating considering system energy losses. This paper investigated a field-oriented control strategy based on maximum torque per ampere (MTPA) control to maximize the output of electromagnetic torque while minimizing stator current, thereby reducing machine copper losses. Additionally, a sliding mode observer was developed to estimate rotor speed and position, serving as software redundancy for speed sensors and enabling sensorless control in fault modes to enhance system reliability. Finally, the control strategy and sliding mode observer were validated using a powertrain simulator in the MATLAB/Simulink environment. Results indicate that MTPA control exhibits a higher power factor and better disturbance rejection. The sliding mode observer can estimate rotor speed and position during non-zero and non-extremely low-speed operation, demonstrating robustness and reliability against disturbances.