ABSTRACT
Islanding refers to the condition of a distributed generation generator continuing to power a location even though power from the electric utility is no longer present. Islanding can be dangerous to utility workers, who may not realize that the solar facility is still powered even though there is no power from the grid. For that reason, distributed generators must detect islanding and immediately stop producing power. Islanding can be detected by passive and active methods resident in the inverter, and by methods not resident in the inverter but present at the utility levels. When the grid is connected and if the grid impedance is smaller than the load impedance, the harmonic current at a particular frequency flows through the grid and no voltage variation is noticed. When the grid disconnects, this current flows through the load. Frequency bias is easily implemented in inverters with a microprocessor-based controller.
