Comparison of Symmetrical and Asymmetrical Cascaded H-Bridge Inverter with Single DC Source

Abstract

This paper presents the comparison of traditional cascaded H-bridge inverter with isolated DC sources (symmetrical arrangement) and the proposed cascaded H-bridge inverter with single DC source (asymmetrical arrangement). Also, fundamental switching strategy is used to generate the control pulses. A conventional cascaded H-bridge (CHB) inverter requires ‘n’ numbers of DC sources for 2n + 1 levels. Without requiring transformers, the scheme proposed here allows the use of a single DC power source (e.g., a battery or a fuel cell stack) with the remaining (n−1) DC sources being capacitors. By maintaining unequal voltage ratios according to a geometric progression with a factor of 2 or 3 at the capacitor voltage, it is possible to obtain the more number of voltage levels with the same number of switches as in the conventional CHB inverter. It is shown that one can simultaneously maintain the DC voltage level of the capacitors and choose a fundamental switching pattern to produce a nearly sinusoidal output and the reduced total harmonic distortion (THD).

Keywords:  Cascaded H-bridge multilevel inverter, fundamental frequency switching, separate DC sources, single DC source.