A Versatile Power Electronic Interface for a Fuel Cell and Ultra-Capacitor Energy Buffer for a DC Micro-grid System

Micro-grid systems are small-scale power supply networks that are designed to provide electricity to a local community from local generators. Micro-grids operate with a common AC or DC bus, and power converters are key components for interfacing the generators and storage devices (and sometimes the loads) to the common bus. The aim of this research study is to investigate and develop high-efficiency power electronic converters for the interconnection of fuel cells and ultra-capacitors to a DC micro-grid for stationary power distribution systems. The converter for the fuel cell and its dynamic control have been designed, simulated, and further improved by introducing a new modified active clamp circuit that enhances performance and increases the efficiency of the converter. This new modification has been designed and verified by PSpice/Simulink approach and implemented using dSPACE. To control the power flow status of the ultra-capacitor, a bidirectional DC–DC converter is required. A number of different alternative DC–DC converter topologies were compared. It was concluded that, the bidirectional voltage–fed topology is better suited for dealing with the fast dynamic response of the ultra-capacitor. However, this topology exhibits a higher circulating power flow and higher conduction losses. Based on this limitation, a modulation scheme that minimises the circulating power flow in the converter was introduced and this was verified by simulations. The hardware for the ultra-capacitor (bi-directional) converter has also been designed and implemented. The test results demonstrate the ability of the converter for fast and bidirectional power flow. The development of simulation models and the control system are experimentally implemented in dSPACE.