Transformerless double-conversion UPS using a regenerative snubber circuit

This paper proposes a transformerless double-conversion UPS, which uses a regenerative Undeland snubber to regenerate the energy from switching losses to the dc bus. The regenerative circuit uses a simple buck-boost QSC (quasi-square-wave) ZVS (zero voltage switching) converter. This auxiliary commutation circuit includes only one active switch and its operation is independent of the UPS operation mode. A detailed methodology is included to design the main components of the auxiliary commutation circuit. Experimental results based on a 1.3 kVA prototype are presented for distinct operation modes to verify the feasibility of the proposed UPS.