A Gallium-Nitride-Device-Based Switched Capacitor Multiport Multilevel Converter for UPS Applications

A novel topology of a modular uninterruptible power supply (UPS) system, based on switched capacitor circuit and wideband gap (WBG) devices, is proposed. This paper deals with the development of a multilevel, multiport, single-phase, transformerless online UPS with universal input/output voltage rating (120-240 V) for main utility and (200-400 V) for the battery packs. The proposed converter mainly relies on capacitors and switching devices to accomplish the task of energy transfer and storage. Compared to conventional topologies, which have multiple power conversion stages, this topology has only one-stage power conversion from ac to dc to ac. The ac output voltage contains five levels whose magnitude comes with a boost functionality. The circuit also does not require the use of inductors or transformers to operate, enabling this topology to be small and lightweight. Moreover, size, cost, and efficiency are improved due to the reduced number of switching devices, passive components, and lack of need for isolation transformers in the multilevel operation. A complete set of simulation and experimental results based on a 2 kVA lab prototype of the proposed UPS is presented to demonstrate its performance under different operating conditions. A peak efficiency of 98.3% has been achieved.