Direct Flux Vector Control of Synchronous Motor Drives: Accurate Decoupled Control with Online Adaptive MTPA and MTPV Evaluation

Direct flux vector control (DFVC) 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 paper 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 (MTPA) and maximum torque per volt (MTPV) control laws, enabling to track the optimal control laws without the need for pre-processed look-up-tables (LUTs). The proposed scheme is experimentally validated on a 1.1 kW synchronous reluctance (SyR) machine test bench.