Switching-Cell Buck-Boost AC-AC Converter with Common-Ground and Noninverting/Inverting Operations

This article proposes a switching-cell-based bipolar buck-boost ac-ac converter that can provide multiple modes of operation, including noninverting buck operation, noninverting boost operation, inverting buck-boost operation, and adjustable noninverting buck-boost operation with two control duty ratios. Each fundamental switching-cell in the proposed converter is composed of a unidirectional buck circuit with no short-circuit or open-circuit problems, increasing its robustness. Hence, safe commutation is naturally realized without the use of RC snubbers or soft-commutation strategies, removing the need for pulsewidth modulation deadtimes. External fast recovery diodes are utilized, avoiding the high-frequency conduction of MOSFET's body diodes and eliminating their slow reverse recovery problem and corresponding power loss. The proposed converter shares a common ground between input and output ports, offers support for reactive loads, draws continuous sinusoidal current from ac mains, and delivers a continuous output current. The converter is suitable for ac voltage regulation applications, notably as a dynamic voltage restorer, compensating extensive magnitudes of both grid voltage sags and swells. Circuit operation and analysis are provided for all the proposed modes of operation. Experimental results obtained using a 400-W laboratory-scale hardware verify the theoretical analysis.