Distributed Generation and Islanding – Study on Converter Modeling of PV Grid-Connected Systems under Islanding Phenomena

Thailand government has launched a 15-year (2008-2022) strategic plan on new and renewable energy. Possible electricity generated from solar photovoltaic has been estimated with a potential of 50,000 MW, whereas at present the cumulative installed wattage is only 32 MW. Under the Plan, numbers of measures and incentives are provided for participation of private very small power producers (VSPP) generating and selling the electricity into the utilities. Most VSPPs generate electricity from renewable sources such as mini-hydro, biogas and biomass, wind and solar. Examples of measures and incentives are the Renewable Portfolio Standard (RPS) for the generating utility and independent power producers (IPP), a feed in tariff with an extra adder, soft loans and tax reduction. The past decade in Thailand has seen shifts from PV used in the public market through government demonstration projects to the consumer market, installations of PV VSPPs and domestic roof-top grid connected PV units gain momentum. With the government incentive more households will be attracted to produce electricity from solar PV and wind energy. As domestic roof sizes are limited, PV roof-top grid-connected units will be of small capacity, less than 10 kW. It is this possible large expansion of market for thousands of small PV rooftop grid-connected units or wind systems in Thailand, and eastern Asia, that draws our attention to the study of single phase distributed generator grid-connected systems. Our focus will be on the anti-islanding protection, which is of concerns to Thai electrical utilities. In order to know the behavior and the effect of anti-islanding techniques, the converter modeling of PV grid-connected systems under islanding phenomena is studied. The approach of modeling is to model a dc-ac full bridge switching converter PV grid-connected system under islanding phenomena using two mathematical modeling techniques. One corresponds to a state-space averaging technique (no linearization) and the other a piecewise technique. The former technique applies a state-space averaging techniqu