Evaluation of a digital control system for a high-efficiency battery charger/UPS

This paper develops a comparison between two control strategies, one well-known analog control system and one digital control system, applied to a battery ZVT bi-directional charger for UPS's. The analog control system is implemented with various dedicated IC's whereas the digital control system, based on digital redesign approach, is implemented with a low cost single chip DSP controller. A prediction algorithm is used to minimize the computation time delay, and an algorithm to determine the sampling instants is developed to obtain the average values of the variables of interest, without noise caused by switching transitions. Experimental results based on a 580 W prototype have been obtained to verify the performance of these control systems.