ONLINE SHE TECHNIQUE FOR CASCADED MULTILEVEL INVERTERS WITH ADJUSTABLE DC SOURCES

Piyush L. Kamani and Mahmadasraf A. Mulla

Keywords

Cascaded H-bridge inverter, multilevel inverter, pulse-amplitude modulation (PAM), selective harmonic elimination (SHE), total harmonic distortion (THD)

Abstract

This paper presents a selective harmonic elimination pulse-amplitude modulation (SHE-PAM) technique for medium- and high-power cascaded multilevel inverters, where the low switching frequency is of prime interest. Instead of nonlinear transcendental SHE equations, this technique calculates switching angles and voltage of dc sources using linear equations formulated by balancing the volt-second area. This reduces computational complexities to a great extent, enabling the online implementation of this technique for an inverter with a higher number of levels, particularly in solar photovoltaic (PV) and STATCOM applications. The suggested SHE-PAM technique controls the output voltage by varying the voltage of dc sources with fixed switching angles. This technique provides the solution for the complete working range of the modulation index. The proposed technique eliminates more harmonics offering reduced total harmonic distortion (THD) compared with the conventional SHE techniques. The theoretical analysis and performance characteristics of the introduced technique are verified with simulation and experimental studies.

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