An approach to improve the torque performance of IPMSM by considering cross saturation applied for hybrid electric vehicle

Permanent magnet synchronous machines are known as a good candidate for hybrid electric vehicles (HEV) due to their unique merits. This paper introduces a method for calculating the output torque by considering the cross saturation between direct-axis (d-axis) and quadrature-axis (q-axis) of an interior permanent magnet synchronous motor (IPMSM). The conventional two-axis IPMSM model is modified to include the cross saturation effect by adding the cross-coupled inductance terms. This paper also calculates the cross-coupled inductance values as well as self-inductance values in d- and q axes. The analyzed motor is suitable machine that offers high torque per ampere per core length at low speed and weakened flux at high speed, which was developed for the traction motor of a hybrid electric vehicle. Using the fact that the motor parameters are nonlinear and significantly vary with direct and quadrature current operating points, a new scheme is generated. This scheme combines the maximum torque per ampere (MTPA) curve, current limit circle, and maximum torque per volt (MTPV) curve, voltage limitations, and torque calculation under the nonlinear parameter variations. As a result, new feedforward tables are generated, which make full use of measured motor parameters. The new torque and flux regulators built around the feedforward tables provide a fast dynamic response and accurate steady-state torque/power production. The proposed controller was implemented and successfully tested on an 18-kW IPM motor hybrid electric drive used in electric vehicle program.