Generalized Circuit Averaging Technique for Two-Switch PWM DC-DC Converters in CCM

Abstract

Design of DC-DC converters like Cuk and SEPIC, which are fourth-order converters, play a vital role in the design of electric vehicle (EV) charging systems and drivers for LED. These converters possess a unique feature of input current being continuous due to the presence of an inductor in series with the supply voltage. In the present work, a generalized approach for obtaining the frequency response of the transfer function of the duty cycle to output voltage (Gvd) for converters operating in continuous conduction mode (CCM) having two switches is proposed. A practical Cuk converter and SEPIC operating in CCM were selected and their analyses in open loop were studied using the LTSpice simulation tool. The behavior of the output voltage and inductor currents under variable ESR’s (equivalent series resistance) of inductors was studied. It was observed that Gvd of these converters was unstable. Hence, an appropriate controller to stabilize the system and achieve a proper gain margin and phase margin in closed-loop operation is required.