Analytical Loss Minimization Control for IPMSM Using Linearized Torque and Loss Modeling

Copper loss minimization schemes are widely used to control interior permanent magnet synchronous motors. In the field-weakening region, the maximum torque per ampere cannot be used due to the voltage limit set by the inverter DC-link voltage. It can be avoided when a high-voltage battery or a boost converter is used in the upstream of the inverter. In such cases, copper loss decreases as the current magnitude decreases. However, higher voltages may increase iron losses. In this article, a control method is investigated to minimize the sum of copper and iron losses. The loss sum is derived as a second-order function of a single flux variable, and the local minimum is determined analytically using the proposed approximation method. The proposed method offers several advantages, including high computational efficiency through analytical determination of the optimal operating point, reliable performance with acceptable approximation errors across various torque and speed conditions, and cost-effectiveness by eliminating the need for extensive dynamometer-based testing. Finally, the study is extended with an application to electric vehicle traction motors. Through simulation and experimental results, the benefits of the proposed control scheme are verified.