An Isolated Bi-directional DC/DC Converter using Unregulated LLC Resonant Converter and Its Design

摘要

This paper presents an isolated bi-directional DC/DC converter comprised of two stages with a hard-switched nonisolated converter and an unregulated LLC converter. The LLC converter operates as an isolated voltage amplifier with a constant voltage gain and the output control can be achieved through the non-isolated converter. By separating functions, the unregulated LLC converter can be designed to have a low switching loss regardless of load conditions. It gives the size reduction of transformer by increasing the switching frequency and a good efficiency under wide load ranges. Furthermore, since the proposed converter uses same gate control scheme for bi-directional control, control is simple and similar efficiencies can be expected under operational modes. Design guidelines based on loss analysis and the experimental results with a 2 kW prototype converter are provided in this paper.