New power conversion technique to obtain high performance and high efficiency for single-phase UPS

Existing power conversion methods for uninterruptible power supply systems (UPSs) can be divided into two categories, passive-standby and double-conversion methods. Generally, the passive-standby scheme has better efficiency while the double-conversion method gives better input and output characteristics. This paper describes a new power conversion method (power multiprocessing conversion method) for single-phase UPSs, which has the merits of both the schemes, providing a high efficiency while maintaining an excellent input and output characteristics. The main circuit based on this new method consists of three phase arms, which operate 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 trial manufactured 1 kVA 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 double-conversion UPSs.