Robust Constant Switching Frequency-Based Field-Weakening Algorithm for Direct Torque Controlled Reluctance Synchronous Motors

This paper presents an improved direct torque controlled reluctance synchronous motor drive for field-weakening applications. The contribution of this paper is twofold. First, a modified direct torque control (DTC) algorithm is proposed to enable a constant switching frequency, reducing the torque ripples significantly while simultaneously retaining the simplicity of the DTC. Conventional field weakening entails the knowledge of the machine parameters that inevitably degrades the robustness and stability of the overall drive system. To circumvent this problem, an improved field-weakening method robust to the machine parameter variations is also presented. These two methods are combined to achieve a robust field-weakening algorithm for direct torque controlled reluctance synchronous motor drives with constant switching frequency and reduced torque ripples. The validity of the proposed algorithm is verified by simulation and experimental results supplemented in this paper.