Off-line UPS system with optimum utilization of power elements

In this paper, a new configuration of an offline UPS system is presented. The system is designed with the least number of power components, which are the most expensive elements of the system, implying optimum utilization of these components. A simple booster winding is connected in series with the high voltage winding of the system transformer during the inversion mode to satisfy the load requirements. The control circuitry of the system is designed to facilitate this arrangement, and to ensure soft and synchronized transfer of the load from and to the mains. A systematic procedure is developed to select the ratings of the power elements of the system, including the booster winding. The availability of these elements, the sensitivity of the load to voltage fluctuations, and the control strategy of the inverter circuit are involved in this procedure. The proposed system was practically implemented, tested, and proved to operate satisfactorily under different loading conditions. It has the features of reduced weight, size, cost and improved reliability.