A Novel Flux-Torque Decoupling Based Direct Torque Control Strategy for Surface Permanent Magnet Synchronous Motor Drives

Direct torque control (DTC) is increasingly attracted for high performance control of surface permanent magnet synchronous motors (SPMSMs) due to its easy implementation and fast dynamic response. However, the conventional switching-table-based method inevitably produces large torque and stator flux ripples because the selection of inverter's active-voltage vector is depending on the sign of torque and flux errors through hysteresis comparators regardless of their amplitude errors. To resolve these problems, a novel DTC strategy based on flux-torque decoupling is proposed in this paper. With the proposed method, two desired voltage vectors are firstly constructed to achieve the decoupling control of stator flux and torque by analyzing the relationships between applied voltage and torque and stator flux derivative. Afterwards, by applying vector synthesis to analyze the generation of two desired voltage vectors, the corresponding inverter's active-voltage vectors and their duty ratios are determined, so as to achieve the precise regulation of stator flux and torque with little ripples. Furthermore, in order to minimize the influence of machine parameters variations, a simple and real-time identification method for the ratio between permanent magnet flux linkage and stator inductance is presented. Finally, the experimental results indicate the effectiveness and feasibility of the proposed strategy.