ANALYSIS AND CONTROL OF TORQUE RIPPLES IN INVERTER-FED PERMANENT-MAGNET SYNCHRONOUS MOTORS USING THE ELECTROMECHANICAL SPRING-STIFFNESS COEFFICIENT DELTA-T(E) DELTA-THETA/

The application of the static electromechanical-spring-stiffness coeff icient partial derivative T(e)/partial derivative theta to the analysi s of torque ripple is presented. Torque ripples of inverter-fed perman ent-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 t he nonuniform-airgap permanent-magnet synchronous motor (PMSM). Contro lling the currents i(d) and i(q) in the manner proposed in the paper, based on the analysis, will result in torques with low ripple content for PMSMs with both uniform and nonuniform airgaps.