A Reliable Single-Phase Bipolar Buck-Boost Direct PWM AC-AC Converter with Continuous Input/Output Currents

In this article, a single-phase bipolar buck-boost direct pulsewidth-modulated ac-ac converter is proposed, comprised of six insulated-gate bipolar transistors, a small film capacitor, and input/output LC filters. The converter can provide discrete noninverting buck (NIBu) and boost (NIBo) operations with voltage gains of D and 1/(1 - D), respectively. Moreover, it provides symmetric noninverting buck-boost (NIBB) and inverting buck-boost (IBB) operations with voltage gains of D/(1 - D) and -D/(1 - D), respectively. It supplies both continuous input/output currents, and it is well suited for reactive loads. It is immune from the commutation problem, and thus, has enhanced the reliability. The various modes of operation of the proposed converter make it suitable for diverse applications, including the following: 1) application as a direct ac voltage regulator when operating in NIBu and NIBo modes; 2) IBB operation can be utilized along with NIBu/ NIBo or NIBB operation to compensate both voltage sag and swell, when used as dynamic voltage restorer; and 3) symmetric NIBB/IBB operations can provide step-changed frequency output, similar to the single-phase matrix converters, for applications as induction motor drive or high-gain ac-dc rectifier. Extensive circuit analysis, component design guidelines, and appropriate comparisons are provided, followed by experimental results obtained using a laboratory prototype.