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

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, research works on DBAC converters are mainly concentrated around unipolar topologies. In a few developed bipolar topologies to 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 (v(in) + v(o) and i(in) + i(o)) 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 for pulsewidth modulation dead times, and elimination of high-frequency conduction of mosfet's body diodes and related slow reverse recovery issues. The proposed converter provides distinct types of efficient inverting and noninverting buck and boost operations, with smaller switch voltage/current stresses (v(in )/ v(o) and i(in )/ i(o)) and passive component ripples. Combined inverting and noninverting buck-boost 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 nonresistive loads. Extensive theoretical analysis is presented followed by practical verifications on a 400-VA laboratory circuit.