US Patent 7408268 Anti-islanding method and system for distributed power generation systems

An electrical power supply system connected to an electrical grid, includes at least one source of electrical power, an inverter which receives power from the electrical source and delivers power to a local load, and a connection to the electrical grid. The system also includes a control unit for controlling the inverter, which interrupts the delivery of power by the inverter when at least one electrical parameter of the system exceeds a threshold value. The system also includes anti-islanding logic which detects at least one symptom of an islanding condition of the system and, when the symptom is detected, to cause a variation in the power level delivered by the inverter.