Optimal Control Strategies for Speed Control of Permanent-Magnet Synchronous Motor Drives

The permanent magnet synchronous motor (PMSM) is very useful in many applications. Vector control of PMSM is popular kind of its control. In this paper, at first an optimal vector control for PMSM is designed and then results are compared with conventional vector control. Then, it is assumed that the measurements are noisy and linear quadratic Gaussian (LQG) methodology is used to filter the noises. The results of noisy optimal vector control and filtered optimal vector control are compared to each other. Nonlinearity of PMSM and existence of inverter in its control circuit caused that the system is nonlinear and time-variant. With deriving average model, the system is changed to nonlinear time-invariant and then the nonlinear system is converted to linear system by linearization of model around average values. This model is used to optimize vector control then two optimal vector controls are compared to each other. Simulation results show that the performance and robustness to noise of the control system has been highly improved. Keywords—Kalman filter, Linear quadratic Gaussian (LQG), Linear quadratic regulator (LQR), Permanent-Magnet synchronous motor (PMSM). NOMECLATURE , d q i i d-q Stator currents , d q v v d-q Stator voltages r ω Electrical speed (rad/s) r θ Electrical position (rad) L T Load torque (N.m) R Phase resistance (Ω) L Phase inductance (Henry) J Rotor inertia (kg.m) D Damping coefficient (N.m.s/rad) φ Permanent magnet flux linkage (N.m/A) N Number of pole pairs