Online Torque Control of IPMSM for Flux Weakening Operation Using Sequential Quadratic Programming

This paper presents an online torque control method for an interior permanent-magnet synchronous motor (IPMSM) operating in the flux weakening (FW) region. The torque control problem in FW operation is formulated as an optimization problem, considering constraints of voltage and current limits as well as a desired torque reference. The proposed method generates the current reference by solving the formulated problem with sequential quadratic programming (SQP) widely used as a solver for nonlinear optimization problem. The proposed method provides an analytic solution considering the effects of magnetic-saturation and variation of flux-linkage; therefore, it is possible to calculate the current reference in real time without pre-constructed look-up tables. In addition, a simplified version of the proposed method is also presented in this paper to implement in the embedded system where the computational burden needs to be minimized. By applying the proposed algorithm, fast torque control is achieved at the two times of base speed. The effectiveness of the proposed method is verified through experiments.