New power conversion technology for single-phase UPS

Abstract

This paper describes a new power conversion method for single-phase uninterruptible power supplies (UPSs). Existing power conversion methods for UPSs can be divided into three categories; off-line, line-interactive and on-line methods. Generally, the line-interactive methods have better efficiency than the on-line method, while the on-line methods give better input and output characteristics than the line-interactive methods. The proposed method has the merits of these methods and provides a high efficiency with maintaining an excellent input and output characteristic. The main circuit based on this new method consists of three phase arms, which operates as a boost converter, a step-down converter, and a power active filter, respectively. Switching loss is significantly reduced by operating the two converters in PWM mode only when necessary. Testing results on a commercialized 1kVA UPS based on the proposed method show a maximum overall efficiency of 94%. Moreover the input and output characteristics are as good as those of the traditional on-line UPSs.