Torque Harmonic Minimization Optimal Pulse Pattern Modulation Technique for Permanent-Magnet Synchronous Motors

Permanent-magnet synchronous motors (PMSMs) inherently exhibit torque oscillations due to their magnetic properties, impacting performance and causing increased noise and vibrations. While pulsewidth modulation (PWM) techniques commonly minimize current harmonics, they often overlook torque fluctuations arising from the interaction between current and back EMF harmonics in PMSMs. Therefore, achieving both minimal torque harmonic content and reduced switching frequency is essential to obtain a smooth torque and low switching losses. This article introduces a novel low-frequency optimal pulse pattern-based torque harmonic minimization (OPP-THM) method, designed to directly minimize torque harmonics in PMSMs, rather than solely focusing on current harmonics. By considering back EMF harmonics in the optimization of switching angles, the proposed approach effectively suppresses low-order torque harmonics without compromising the contribution of back EMF harmonics to average torque, thereby enhancing the PMSM performance. The effectiveness of the proposed method is demonstrated through validation on a 4-kW experimental PMSM drive employing field-oriented control (FOC) under steady-state and transient conditions.