Simulation of A Direct Torque Controlled PMSM Drive Incorporating Structural and Saturation Saliencies

The direct torque controlled permanent magnet synchronous motor (PMSM) drive system has become competitive compared with other types of drive systems, because of its simple and sensorless control algorithm. The practical application of the system, however, is handicapped by the difficulty of starting under full load due to the unknown initial rotor position. The most versatile methods for initial rotor position detection make use of the structural and magnetic saturation saliencies of the PMSM. Since the conventional PMSM model does not incorporate the saturation saliency, when developing a new method for the initial rotor position detection, it is not possible to numerically simulate the method, and the experimental trial and error method is widely employed. This paper presents a nonlinear model of PMSMs which incorporates both the structural and saturation saliencies to enable the numerical simulation of new rotor position detection algorithms. In this model, the self and mutual incremental inductances of the phase windings are expressed by Fourier series as functions of the stator current and rotor position. The experimental measurement of the incremental inductances is outlined in the paper. Based on the model, the direct torque control scheme is simulated using the Matlab/Simulink package. To verify the validity of the new model, the simulation results are compared with the results of the conventional PMSM model in the Simulink library.