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

The direct torque controlled (DTC) permanent magnet synchronous motor (PMSM) drive has become competitive compared with other types of drive systems because of its simple and sensorless control algorithm. The application of the system, however, is handicapped by the difficulty of starting under full load due to the unknown initial rotor position. This paper presents a nonlinear model of PMSMs which incorporates both the structural and saturation saliencies to enable the numerical simulation of initial rotor position detection algorithms. In this model, the phase inductances are expressed by Fourier series as functions of the stator current and rotor position. The inductances of a surface mounted PMSM is measured with different rotor positions and DC offset currents, which emulate the effect of the three phase stator currents. By using the proposed model, the DTC PMSM is simulated and the results are compared with those obtained by the PMSM model in the Simulink library. With the model, an initial rotor position estimation scheme using voltage pulses is investigated by numerical simulation. The scheme is also experimentally tested and the results are compared with the inductance variation to verify the validity of the method. The effectiveness of the scheme to estimate the initial rotor position for the testing SPMSM is analyzed and verified by numerical simulation before physical implementation