Highly Efficient Dual-Buck Structured Buck–Boost AC–AC Converter With Versatile Identical Inverting/Noninverting Operations

Abstract

Single-phase dual-buck ac-ac (DBAC) converters are gaining attention due to their intrinsic protection from shoot-through and open-circuit problems of conventional ac-ac converters. However, researches on DBAC converters are mainly concentrated around unipolar topologies. In a few developed bipolar topologies till date, the inverting buck-boost operations (for series voltage injection and step-variable frequency outputs) are inefficient and burdened by large voltage and current stresses ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v_in + v_o</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_in</i> + <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_o</i> ) of switching devices and ripples of passive elements. In this article, an efficient dual-buck structured buck-boost ac-ac converter is proposed, with the following features: no voltage source shoot-through and inductor open-circuit problems, natural attainment of safe-commutation without additional protection circuitry or complex control, no need of PWM dead-times, and elimination of high-frequency conduction of MOSFET's body diodes and related slow reverse recovery issues. The proposed converter provides distinct type efficient inverting and non-inverting buck (EINIBu) and boost (EINIBo) operations, with smaller switch voltage/current stresses ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v_in</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v_o</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_in</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_o</i> ) and passive component ripples. Combined inverting and non-inverting buck-boost (CINIBB) operations are also proposed with separate tuning of buck and boost voltage transfer ratios. A simple adaptable switching strategy provides the switch control pulses for all circuit operations by modulating the buck and boost control reference signals. The proposed converter provides sustained input/output currents and performs well with non-resistive loads. Extensive theoretical analysis is presented followed by practical verifications on a 400-VA laboratory circuit.