Direct Flux Vector Control of Synchronous Motor Drives: Accurate Decoupled Control With Online Adaptive Maximum Torque Per Ampere and Maximum Torque Per Volts Evaluation

Direct flux vector control has an unique advantage in facilitating flux-weakening operation due to the choice of controlled variables: stator flux linkage magnitude and torque producing current. However, the dynamics in stator flux oriented reference frame is heavily affected by the nonlinear cross-coupling between the two axes. This article presents a nonlinear transformation method to decouple the axes for a uniform bandwidth at all operating points. Respect to the literature, the proposed transformation takes magnetic saturation into account without approximation. Furthermore, the auxiliary-flux and auxiliary-current vectors are introduced to design a new adaptive evaluation of maximum torque per ampere and maximum torque per volt control laws, enabling to track the optimal control laws without the need for preprocessed lookup tables. The proposed scheme is experimentally validated on a 1.1 kW synchronous reluctance machine test bench.