Bi-directional Zero-current Soft-switching Technique Applied for Bi-directional DC-DC Converter in Energy Capacitor Systems

Abstract

In our previous work, we proposed the current-source energy capacitor system (CS-ECS), which consists of an electric double-layer capacitor, current-source inverter, and bi-directional four-quadrant DC-DC (FQ DC-DC) converter to control active/reactive power that can achieve the output leveling of wind energy system. However, this system had low conversion efficiency due to hard-switching losses. The improvement of conversion efficiency and performance are indispensable to implement the CS-ECS. This article proposes the soft-switched FQ DC-DC converter with a simple L-C resonant circuit for the CS-ECS. Since the insulated gate bipolar transistors of the converter softly turns on and off by using current-mode resonance, the conversion efficiency for the proposed system improves. In order to illustrate the operating principle of the proposed system, we analyze the transition of conversion efficiency with charge and discharge operation in detail through a theoretical approach and computer simulations with MATLAB/SIMULINK and SimPowerSystems Toolbox.