Design and Implementation of a Bipolar AC-AC Converter with Solving the Commutation Problems

In this paper, a single-phase direct AC-AC buckboost converter with pulse-width modulation is proposed, comprising four IGBTs with diodes, two IGBTs without diodes, four fast diodes, a small film capacitor, and an input/output LC filter. The converter is capable of operating in three modes: noninverting buck, non-inverting boost, and inverting buck-boost, with gain values of $D, 1 /(1-D)$, and $-D /(1-D)$, respectively. High reliability is achieved in this converter through the elimination of commutation problems, such asthe risk of short-circuiting between the capacitor and input source, as well as the opencircuiting of inductor current, which could otherwise cause severe voltage spikes across the semiconductors. Since no deadtime is required between complementary switches, high-quality output voltage can be generated. The various operating modes of this converter make it suitable for applications as a voltage regulator and as a DVR to compensate for voltage sags and swells in the grid. Theoretical analysis, operating modes, switching strategy, and component design are provided, along with a 500 W experimental prototype and its results.