AC-AC Converters

AC-AC converters broadly define a set of power electronic topologies employed to obtain AC output of variable amplitude and frequency from fixed AC input without employing bulky reactive components. The converters that give variable amplitude AC and an unchanged frequency are known as voltage controllers and those that produce variable frequency AC are classified as cycloconverters and matrix converters (MCs). The cycloconverters commonly employ naturally commutated thyristors, while the MCs employ integrated gate bipolar transistors that are forced commutated. Variation of the frequency in the cycloconverters is restricted to only a fraction of the supply frequency. In contrast, MCs are employed for an unrestricted frequency change but with less voltage transfer ratio. MC employs fast switching bidirectional switches and consists of two types, namely direct MC (DMC) and indirect MC (IMC). This chapter discusses the single-phase and three-phase AC-AC voltage regulators in detail. Then, a detailed discussion on single-phase and three-phase cycloconverter operation is presented. Further, the 3×3 DMC circuit and its modulation schemes are discussed in detail and complemented with simulation in the MATLAB environment. New advances in the AC-AC technology are discussed. The new topologies in the field of MCs are multilevel MC, multimodular MC, and sparse MCs. Z-sourced DMC and IMC are considered as they boost the voltage transfer ratio and reduce commutation problems. AC-AC converters have a wide range of applications, from traction to household voltage regulators. However, MCs are restricted to the niche applications like military tanks and more electric aircraft due to the absence of intermediate energy storage.