Torque analysis and control of a double-layer interior permanent-magnet synchronous motor for electric vehicle propulsion applications

In the first part of the paper, the electromagnetic torque of a double-layer interior permanent-magnet synchronous motor (DLIPMSM) for electric vehicle (EV) propulsion is analyzed using the finite-element field solution in the motor cross-section. Pulsating torque components are then evaluated, and a practical method to mitigate them by step-skewed PM-rotor design is applied in order to improve the electromagnetic torque quality. In the second part of the paper, the hysteresis-based direct torque and flux control (DTFC) scheme of DLIPMSM for EV propulsion applications is argued, and a novel approach for generating the reference stator flux-linkage vector magnitude is proposed to insure DLIPMSM extended torque-speed envelope with maximum torque-to-stator current ratio operation in the constant-torque region below the base speed, as well as constant-power flux-weakening operation with highest available torque in the region above the base speed. Experimental results for DLIPMSM steady-state characteristics and dynamic torque response under the new hysteresis-based DTFC over wide-speed operating range are provided and discussed.