Harmonic Elimination Technique in Three-Phase Five-Level Cascade H-Bridge Multilevel Inverters from Three-Phase Perspective

This paper proposes an alternative approach to finding the unknown switching angles of three-phase five-level cascade H-bridge multilevel inverters using the selective harmonic elimination PWM technique from the three-phase perspective over a wide range of modulation indices to improve Total Harmonic Distortion (THD). A mathematical model is introduced to find the pre-calculated angles using a three-phase modulation perspective in the interval (0, pi/3) to eliminate selective harmonics on single-phase topologies that are used to construct three-phase inverters in high-power application. Looking from the three-phase perspective in the interval (0, pi/3) to find the unknown angles improves the output in comparison with the interval (0, pi/2) when looking from the single-phase perspective. Both approaches eliminate the selected harmonics; however, the proposed approach decreases the output voltage THD by 25% and increases the minimum value of the fundamental component by 125%. Further, finding the angles using the proposed method guarantees the desired shape of the voltage signal, further guaranteeing a minimum amplitude for the output generated voltage at low modulation indices. Simulation and experimental results are presented to validate the proposed method.