Hybrid SHM-SHE Modulation Technique for a Four-Leg NPC Inverter With DC Capacitor Self-Voltage Balancing

This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Abstract—In this paper, SHM (Selective Harmonic Mitigation) and SHE (Selective Harmonic Elimination) modulation techniques have been combined to produce appropriate pulses for four-leg three-level NPC (Neutral Point Clamped) inverter. In the proposed hybrid method, SHM technique is applied to phase legs in order to mitigate non-triplen harmonics (5 th , 7 th , …) and the fourth leg is controlled by SHE principle to eliminate important low order triplen harmonics (3 rd , 9 th , …) completely. In this context, it is demonstrated that using SHM instead of SHE modulator for phase legs leads to reduce vast range of harmonic orders in the NPC output voltage, significantly. Moreover, it is proved that presented hybrid switching technique has the ability of DC bus capacitors voltages balancing, inherently. Furthermore, analyses are performed to calculate the DC bus capacitances accurately to show 5% voltage ripple acceptably. Simulation and experimental results validate good dynamic performance of proposed hybrid modulation technique in firing the NPC inverter switches to generate low harmonic voltage waveforms supplying balanced and unbalanced loads while balancing the DC capacitors voltages in four-wire network with small DC link capacitors.