Closed Loop Control of Induction Motor Operated with Hybrid PWM(SVM+SOPWM) at Low Switching Frequency for Traction Applications

This paper addresses challenges related to harmonic distortion in closed-loop control systems for high-power traction motors operating at low switching frequencies (<400 Hz) using a 2-level inverter. While low switching frequencies aim to minimize semiconductor switching losses, they often lead to increased harmonic distortion, motor losses, and torque ripple. To tackle these issues, the paper proposes a novel pulse width modulation (PWM) technique that integrates asynchronous and synchronous space vector modulation (SVM) with synchronized optimal modulation for a 2-level inverter. The PWM method incorporates various pulse numbers, including SVM-based asynchronous pulse numbers, SVM-based synchronous pulse numbers (21, 15), and synchronous optimal (SOPWM) pulse numbers (11, 9, 7, 5, 3). The SOPWM technique exclusively employs continuous optimal switching angles for true optimality through nonlinear constrained optimization, without considering post-optimization techniques. Furthermore, the proposed PWM technique enhances the fundamental voltage without the need for pre-modulation. Experimental results, demonstrating the efficacy of the PWM technique in reducing harmonic distortion and improving motor performance, are presented for a two-level inverter feeding an induction machine in a closed-loop control manner across the entire speed range.