Permanent magnet synchronous motor drive for HEV propulsion: optimum speed ratio and parameter determination

The main objective of this paper is to determine the optimum speed ratio (i.e., the ratio of maximum to rated speed) of PMSM applied to hybrid electrical vehicle (HEV) propulsion while taking into account motor performance figures of merit (i.e., peak power, continuous power, total weight (volume), loss components, and average efficiency). PMSM are designed for different rated speeds using scaling equations to compute loss components, total weight and motor dimensions. The direct-axis reactance, quadrature-axis reactance and PM back-emf are determined using a procedure that minimizes the motor continuous power. Under certain flux-weakening operating conditions, the total armature current may increase over the current at peak power and rated speed regardless of the motor power and speed. At high speeds (frequencies), the eddy-current loss becomes predominant, reducing the high-efficiency advantage that the PMSM finds in constant-speed applications. The paper shows that the PMSM performance is very sensitive to the speed ratio and the motor parameters, which for HEV traction applications require careful design selection.