Flux-Weakening Control of IPM Motors With Significant Effect of Magnetic Saturation and Stator Resistance

In this paper, we propose a systematic optimization approach to flux-weakening control of interior permanent-magnet (IPM) motors, which operate in magnetic saturation. The current commands are chosen to be optimal so as to minimize power loss not only in the constant-torque region but also in the constant-power region. Our approach aims at the same objective as the previously known flux-weakening control. Furthermore, the motor torque of an IPM motor in magnetic saturation can be made exactly linear with respect to the torque command. Thereby, our systematic approach can provide not only maximal power efficiency but also torque linearity. In doing so, we consider a more general situation than that considered in prior literature. Specifically speaking, the physical constraints in stator currents and voltages, and the effect of stator resistance are all taken into full account. As a result, the optimization problem becomes very complicated. Nonetheless, we have successfully found the approximate optimal solution, which can be readily implemented on a usual high-speed microprocessor. The practical effectiveness of the proposed control method is also demonstrated through various simulation and experimental results.