Online MTPA Operation of IPMSM Based on Dual-Loop Control in Polar Coordinates

In this article, a maximum online torque per ampere (MTPA) control is proposed for torque control of interior permanent magnet synchronous motors. First, torque and MTPA equations are derived based on flux variables, where the influence of magnetic saturation and cross-coupling effects is carefully considered. These equations can be described in polar coordinates, in which the output torque and MTPA operation are mainly determined by the current magnitude and current angle, respectively. Consequently, a dual-loop controller is proposed to solve the torque and MTPA equations in polar coordinates with a lower computational burden. It consists of a current magnitude and a current angle controller, where a torque reference limiter is embedded to satisfy the current limit. Moreover, the current angle is set within a stable range to avoid the stuck of the controller. The effectiveness of the proposed method is verified through simulation and experimental results. Applying the proposed algorithms, both MTPA operation and torque accuracy can be achieved with less computational burden.