Pulsating torque reduction for permanent magnet AC motors

Control methods for the pulsation of torque reduction for the surface-mounted permanent magnet motors are discussed. 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. The proposed control method is an estimator based. To ensure parameter convergence the Lyapunov direct method is used in the estimator design for the flux Fourier coefficients. A novel nonlinear torque controller based on the 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 the internal model principle and adaptive feedforward compensation technique. An overall control scheme and experimental results are also presented.