Torque Control of IPMSM in the Field-Weakening Region With Improved DC-Link Voltage Utilization

In the field weakening region, the voltage is utilized to the maximum to minimize the current amplitude. In this paper, the hexagonal voltage limit is considered to increase the voltage and to decrease the current, as a result to reduce the copper loss. At first, an intersection between the hexagonal voltage limit and torque curve was found. Because the intersection lies on the boundary of the hexagon, the equations of the sides of the hexagon were derived. Since the hexagonal voltage limit rotates in the synchronous reference frame, they are a function of the rotor position. Finally, the voltage angle was calculated from the intersection. To reduce the torque ripple, d-axis current feedback was added to the voltage angle. In the simulation and experiment results, an increase of voltage and a decrease of current were observed. In addition, an improvement of the motor and inverter efficiencies was also achieved.