Model Predictive Direct Self-Control for Six-Step Operation of Permanent-Magnet Synchronous Machines

Abstract

The optimization of voltage utilization can boost electric drives' power and torque capabilities, which is of particular interest in transportation applications. However, this is a weak point of most control approaches, like linear field-oriented control (FOC) methods using standard modulation schemes. This paper introduces the model predictive direct self-control (MPDSC) strategy, a modification of direct self-control (DSC) for its application in a digital implementation to achieve maximum voltage utilization (i.e., six-step operation) for permanent magnet synchronous machines. This solution is suitable for highly utilized machines with heavy magnetic (cross-)saturation and low sampling to fundamental frequency ratio. The modifications include using load angle regulation to control the selected operating point and model prediction to compensate for the actuation delay. The proposed system can achieve six-step operation with accurate torque control and robustness against disturbances and parameter estimation inaccuracies. Comprehensive simulation and experimental results demonstrate the performance of the proposed MPDSC while operating at the voltage constraint. In particular, a transient rise time of 2.3 ms to maximum torque, current reduction for equal torque-speed operating point of up to 18 %, and maximum torque increase for equal current amplitude of up to 15 % compared to conventional FOC have been empirically observed.