14 - AC-AC Converters

Abstract

Ac-ac converters broadly define a set of power electronic topologies that are employed to obtain ac output of variable amplitude and frequency from fixed ac input without employment of bulky reactive components. A converter that gives variable amplitude ac is known as a voltage controller and that employed for variable-frequency ac is known as cycloconverter. Depending on the operation of thyristors, cycloconverters can be naturally commutated (NCC) or forcefully commutated (FCC). Variation of the frequency in the NCC is restricted to only half of the supply frequency. In contrast, FCC is employed for unrestricted frequency change but with less voltage transfer ratio. Matrix converter (MC) is a kind of FCC that employs fast switching bidirectional switches and is of two types, namely, direct (DMC) and indirect MC (IMC). New topologies in the field of MCs are multilevel MC, multimodular MC, and sparse MCs. Z-source DMC and IMC are considered as it boosts up in the voltage transfer ratio and reduces the commutation problems.