A Novel Torque Harmonics Suppression PWM Method of High-Speed PMSG for Microturbine Power Generation System

As microturbine (MT) power generation systems usually operate at high speeds, the switching-to-fundamental frequency ratio (SFR) reaches excessively low due to the limited switching frequency of the pulsewidth modulation (PWM) rectifier, resulting in undesirable electromagnetic torque harmonics that seriously hinder the torque performance and stability of the system. To restrain the electromagnetic torque harmonics under high speeds and low SFRs, this article proposes a novel torque harmonic suppression PWM (THSPWM) method for high-speed permanent magnet synchronous generators (HSPMSGs) in MT power generation systems. In this article, the analytical electromagnetic torque equation is derived in the $dq$ coordinate system as a function of the stator voltage under synchronous modulation, which takes the salient pole ratio and the load angle of HSPMSGs into consideration. Based on the derived analytical torque equation, a torque harmonic evaluation index is proposed as the optimization objective, and the THSPWM method can be established by optimizing the switching angles of the stator voltage to minimize torque harmonics. Finally, the effectiveness in suppressing torque harmonics of the proposed THSPWM method is verified on the HSPMSG platform.