Abstract

Applications that require exchange of power from the source to the load and vice-versa have conventionally been implemented with two uni-directional converters; each processing the power in one direction. With growing emphasis on compact, smaller and efficient power systems there is increasing interest in the possibility of using bi-directional converters, especially in DC power based applications like space, telecommunication and computer systems. A bi-directional dc-dc converter, capable of bilateral power flow, provides the functionality of two uni-directional converters in a single converter unit. This thesis proposes a topology for a bi-directional dc-dc converter for use in low power applications. The implementation of this converter topology for a battery charger/discharger circuit, with applications in DC UPS systems, demonstrates its feasibility and advantages when compared to the conventionally used circuits. The topology is based on a half-bridge on the primary and a current fed push-pull on the secondary side of a high frequency isolation transformer. The small signal and steady state analyses of the proposed topology are presented. Characteristic curves generated from the analysis aid the design of a laboratory prototype as demonstrated by a detailed design example. Experimental results from the prototype, under different operating conditions, validate and evaluate the topology. Achieving bi-directional flow of power using the same power components provides a simple, efficient and galvanically isolated topology for a low power bi-directional dc-dc converter.