A Modified Direct Torque Control Using Space Vector Modulation (DTC-SVM) for Surface Permanent Magnet Synchronous Machine (PMSM) with Modified 4-order Sliding Mode Observer

For the original DTC-SVM methods, torque would decrease in steady state which could deteriorate the system performance. To fix this problem, the paper proposed a modified DTC-SVM method by introducing additional speed feedback. In the proposed strategy, the prediction of stator flux is divided into two parts which can make PI controller work more effective. Then the authors modified the sign function in the 4-order sliding mode observer and used it for surface-PMSM to obtain stator flux and speed information. The simulation results show that system performance can be improved both in steady state and dynamic state with the modified control method and the chattering of estimated speed can be greatly reduced with the modified sliding mode observer.