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.