An Optimized Hybrid Unipolar PWM Technique for Ripple Reduction in Flying Capacitor of 5L-ANPC Converters

Abstract

Five-level active neutral-point-clamped (5L-ANPC) converters have emerged as promising solutions for various industrial applications owing to their outstanding performance and control simplicity. Unipolar pulse width modulation (PWM) is a widely adopted control strategy for these converters, known for its capability to generate a desired five-level output voltage while maintaining balanced dc-link and flying capacitor (FC) voltages. However, unipolar PWM frequently results in significant ripple currents in FCs, potentially diminishing their lifespan and overall system reliability. To address this challenge, this article proposes current ripple-reduction strategies over a wide modulation index (MI) range. Six ripple-elimination methods are presented and compared against the conventional unipolar PWM. These methods aim to significantly reduce FC current ripples while ensuring acceptable levels of output voltage distortion. A hybrid switching method tailored to accommodate various MI operations is suggested. It can enhance the performance and reliability of these converters in various industrial applications.