New field weakening technique for high saliency interior permanent magnet motor

This paper describes a novel field weakening technology of IPMM (interior permanent magnet motor) for the extended torque control capability. The proposed method controls the magnitude of flux according to the speed and DC link voltage without losing the ability to regulate the command torque. The control adjusts the d and q-axis current reference toward the operating point with a reduced field magnitude along the constant torque curve. Moving along the constant torque curve insures proper torque linearity even in the field-weakening region. By combining closed-loop control using the output voltage and feed-forward control with the pre-calculated tables, the proposed strategy can achieve fast dynamic control as well as parameter insensitivity in the field-weakening region. The proposed field weakening algorithm is implemented and tested using both a 6 kW IPMM designed for the 42 V ISG (integrated starter generator) application and a 70 kW IPMM used for the electric vehicle propulsion application. The experimental results are presented herein to validate the steady state and dynamic performance of the proposed algorithm.