A converter topology to interface low voltage Solar/Fuel Cell type energy sources to electric utility

Solar and fuel cells are some of the most promising energy sources for future energy generation. However due to their variable and low magnitude voltage a power conditioner capable of providing a large voltage gain is required. This is especially true in applications supplying power to AC loads or the electric grid in which a voltage gain around 8 p.u. is required. The traditional approach to implement the power conditioner in single phase applications is by cascading an isolated DC-DC converter with a DC-AC inverter. However this results in a system of larger size and cost due to the need of a high frequency transformer and the presence of a large second harmonic component in the DC link current. An alternative to the traditional approach is presented in this paper in which a high gain transformer-less DC-DC converter and Z-source inverter are used. It is shown that due to inductor losses the maximum voltage gain of the Z-source inverter is limited. And therefore a two stage approach is a more suitable solution. It is also shown, by means of simulations, that by combining the Z-source inverter with the transformer less DC-DC converter a system with improved performance is obtained.