A Practical Analytical Expression and Estimation for Average Torque of High Saturation Permanent Magnet Synchronous Motor for Special Vehicles

Torque is a significant parameter in the design and control of permanent magnet synchronous motor (PMSM). Torque measurement systems are usually expensive, which correspondingly require extra room and add weight. Alternatively, torque can be estimated by the product of the measured current and the estimated magnetic flux. In general, the conventional torque estimation method for PMSM is established based on ignoring core saturation. However, in special vehicles, due to the high power density and narrow installation space of the motors, the saturation degree of the core is high, and the nonlinear characteristic between torque and current is more prominent, which would bring significant errors to the conventional torque estimation method. In order to solve the aforementioned problem, this paper studies on the torque from the perspective of magnetomotive force (MMF). A saturation coefficient is proposed to modify the conventional torque model by considering the core reluctance. Then, a practical analytical expression of average torque and an improved torque estimation method are proposed. Compared with the conventional method, the proposed method significantly improves the accuracy of the estimation. At last, comprehensive simulation and experimental results based on a prototyped 300 kW interior PMSM have fully demonstrated that the proposed method can get accurate torque under different load conditions.