Pulsating torque reduction for permanent magnet AC motors

Control methods for pulsation of torque reduction for the surface-mounted permanent magnet motors are discussed in the paper. The pulsation torque is a consequence of the non-sinusoidal flux distribution and due to interaction of the rotor's permanent magnets with the changing stator reluctance. Proposed control method is estimator based. To assure parameter convergence Lyapunov's direct method is used in estimator design for the flux Fourier's coefficients. Novel nonlinear torque controller based on flux/torque estimate is introduced to reduce the influence of the flux harmonics. The influence of the cogging torque is considerably reduced at lower motor speed using internal model principle and adaptive feedforward compensation technique. Overall control scheme and experimental results are also presented.