In this paper, as in the control method for high-dynamics drives, the authors have designed a control system for UPS based on a double regulation loop, which allows the response time during load transients to be reduced. The main feature is the control of the current flowing through the filter capacitor so that it can be limited within a given range. This is enabled by the internal current loop. The external voltage loop makes it possible to obtain better dynamic response in comparison with conventional systems. The advantages of such a solution are the following: 1) very good dynamic responses to load variations; 2) simpler determination of the current in the switches. Digital simulations of both the power and the control systems have been performed using the EMTP general purpose program.