Analysis and control of torque ripples in inverter-fed permanent-magnet synchronous motors using the electromechanical spring-stiffness coefficient ∂Te/∂&thetas;

The application of the static electromechanical-spring-stiffness coefficient ∂T_e/∂θ to the analysis of torque ripple is presented. Torque ripples of inverter-fed permanent-magnet synchronous motors with uniform and nonuniform airgaps are analysed. It is shown that the quadrature current not only contributes to the electromagnetic torque but also affects the torque ripple in the nonuniform-airgap permanent-magnet synchronous motor (PMSM). Controlling the currents i_d and i_q in the manner proposed in the paper, based on the analysis, results in torques with low ripple content for PMSMs with both uniform and nonuniform airgaps