Torque Ripple Reduction in Interior Permanent Magnet Synchronous Machines Using the Principle of Mutual Harmonics Exclusion

The interior permanent magnet (IPM) synchronous machine is vulnerable to developing significant amounts of current-induced ripple torque depending on the details of the machine design. Building on the contributions of earlier researchers, this paper approaches the problem of torque ripple reduction in IPM machines by applying the principle of mutual harmonics exclusion. First, this paper develops a useful analytical expression for the torque ripple that highlights the stator-rotor harmonic interactions. Next, an analytical design procedure for IPM rotors with multiple flux barriers is proposed that applies the mutual harmonics exclusion principle in combination with stator windings that use odd numbers of slots per pole pair. Finally, the technique is applied to two example IPM machines to investigate the effectiveness of this approach using finite element analysis. Promising results predict that a low peak-to-peak torque ripple can be achieved using relatively small numbers of stator slots and rotor flux barriers for the full range of current control angles, including deep flux weakening.