An innovative, efficient current-fed push-pull grid connectable inverter for distributed generation systems

Environmentally friendly power sources such as photovoltaic solar cells, small scale wind turbines and fuel cells are particularly suitable for distributed generation systems, but typically produce a relatively low magnitude DC voltage output that can vary significantly as operating conditions change. Hence a power electronic inverter is required to condition this output into a more conventional constant magnitude AC supply voltage. Such an inverter should be light weight, low cost, efficient, and provide galvanic isolation between the source and the AC output/grid connection. It is also often preferable that the inverter draws constant DC current from the input energy source, which means it must smooth out the double-fundamental-frequency energy flow of a single phase AC load connection. These requirements can be met with a double conversion system incorporating a high frequency DC-DC step up converter to produce a relatively constant high voltage DC output from the varying DC input, and a high voltage DC-AC inverter and filter to produce the final AC output. This paper describes the winning entry inverter developed by the Monash University FEC undergraduate team for the 2005 IEEE Future Energy Challenge to meet these requirements. The specifications for the inverter were quite challenging in terms of input voltage range, efficiency, volume weight and cost. Design details, innovations, and simulation and experimental results are included in the paper.