Simulation studies of islanded behavior of grid-connected photovoltaic systems

Simplified computer models are presented for predicting the run-on time of self-commutated inverters operating in a utility interactive mode. The inverter receives DC power from a photovoltaic (PV) array and delivers AC power to a local load or the utility lines. The models represent the dynamics of a phase-locked loop control circuit that is designed to destabilize the inverter operation and shut down the power-conditioning subsystem when a phase discrepancy between the line and some reference signal is detected. The sustained isolated operation (or islanding) of the PV system poses a possible safety concern to utility personnel and potential damage to utility-connected equipment. Two computer models, the TESLACO model and the APCC model, were implemented on an IBM PC using Pascal. They provide results compatible with experimental evidence and more elaborate computer modeling techniques.<>