Asymmetrical multilevel inverter topologies

Abstract

Renewable energy sources such as solar, wind, tidal, or biomasses are utilized to generate electrical energy without CO2 emission. Most of the generated energy, either AC or DC, is requested to be converted to AC for industrial use. Inverters, which are studied for achieving higher efficiency and reliable systems, are classified based on output voltage levels as two level for conventional and multilevel for recent inverter topologies. Multilevel inverters provide three or more levels at the output voltage and current waveforms. The conventional multilevel inverter topologies, known as diode clamped, flying capacitor, and cascade H-bridge, involve different requirements such as separate DC sources or clamping devices. The asymmetric multilevel inverters are based on conventional topologies using different magnitudes of DC voltage ratios and separated DC sources. Such an operating principle provides a rational increment at the output waveform level by using the same or a lower number of switching devices compared to conventional symmetrical topologies. Asymmetric multilevel inverter topologies are classified according to structural properties such as cell form and polarity changer modules. All the asymmetric topologies can be used in symmetric mode. When the magnitude ratio of the voltage sources is increased as a power of two (i.e., Vi, 2Vi, 4Vi, 8Vi), this type of inverter is called the binary asymmetrical topology, while the trinary topology is comprised of a power of three at separated DC voltage levels, as Vi, 3Vi, 9Vi, 27Vi. This chapter introduces asymmetrical multilevel inverter topologies, with simplified, switched capacitor, cascaded asymmetrical, and similar other applications presented in detail. In addition to regular topologies, novel asymmetrical multilevel inverters are discussed.