Switching loss reduction of AC-AC converter using three-level rectifier and inverter for UPS

This paper proposes an AC-AC converter, which consists of T-type three-level rectifier and inverter, for an on-line UPS. The switching loss of the proposed AC-AC converter is drastically reduced because the proposed converter is driven at a very low switching frequency which is six times of input side frequency. The T-type rectifier separates the maximum phase-voltage, medium phase-voltage and minimum phase-voltage from the input voltage. Next the output waveform is built by the T-type inverter from each maximum phase-voltage, middle phase-voltage and minimum phase-voltage. The proposed circuit can achieve not only high efficiency, but also short instantaneous interruption time. Furthermore, the proposed AC-AC converter compensates a voltage dip with changing an operation mode of a rectifier. In this paper, the fundamental operation of the proposed converter is confirmed by simulations and experiments. In addition, the power loss of the proposed converter is compared to a conventional on-line UPS and the efficiency of the proposed converter is 97.1% at rated load in an experiment.