Robust Current Controller for IPMSM Drives Based on Explicit Model Predictive Control With Online Disturbance Observer

To improve the performance of a current loop, this paper presents a novel current control scheme for an interior permanent magnet synchronous motor (IPMSM) based on the model predictive control (MPC) algorithm in a synchronous rotating frame (dq-frame). The recently developed explicit MPC (EMPC) is introduced to ensure the feasibility of real-time implementation in the control hardware. To achieve feasible reformulation of the current control problem using EMPC, a coupled nonlinear IPMSM mathematical model is linearized using an augmented model with disturbance. Furthermore, to approximate the related quadratic stator current and voltage constraints in the dq-frame, they are also transformed into a series of linear inequalities. We propose an improved disturbance observer based on the augmented model, in conjunction with the concept of offset-free MPC, to estimate both the disturbance terms and the state variables from the predicted and measured outputs. All the influences of plant/model mismatches and un-modeled nonlinear terms are removed by the estimated total disturbance within the closed-loop framework of EMPC. The proposed EMPC scheme not only improves both the dynamic performance and the steady-state precision of the current loop, but it also exhibits robustness against parameter uncertainties. The proposed method has been proven and verified successfully in both simulation and experiment.