Anti-islanding method and system for distributed power generation systems

A method for controlling a power supply system connected to a power grid, the power supply system including an electrical power source, an inverter connecting the electrical power source to the power grid, and a load connected to the inverter, the method comprising:

• delivering power to the load;
• detecting a characteristic indicative of an islanding condition of the system;
• when the characteristic is detected, imposing a temporary variation in the power level delivered by the inverter,
• detecting a characteristic indicative of an islanding condition of the system while there is a temporary variation in the power level delivered by the inverter;
• and
• interrupting the delivery of power to the load in response to detecting a characteristic indicative of an islanding condition of the system while there is a temporary variation in the power level delivered by the inverter.

A method for controlling a power supply system connected to a grid, the power supply system including an electrical power source, an inverter connecting the electrical power source to the grid and a load connected to the inverter, comprising the following phases:

• delivering power to the load;
• determining a symptomatic condition of islanding of the system;
• when a symptomatic condition of an islanding situation is determined, imposing a variation in the power level delivered by the inverter;
• if the variation in power level delivered by the inverter causes a variation beyond a pre-set limit of an electrical parameter of the system, causing interruption of the power delivery via the inverter.

An electrical power supply system connected to a local load and to an electrical grid comprising:

• at least one source of electrical power;
• an inverter which receives power from the electrical source and delivers power to the local load;
• a connection to the electrical grid;
• a control unit functionally connected to the inverter, the control unit comprising interrupt logic functional to interrupt the delivery of power;
• the control unit further comprising anti-islanding logic functional to detect at least one symptom of an islanding condition of the system and, when the symptom is detected, to cause a variation in the power delivered by the inverter;
• and
• wherein the anti-islanding logic is further functional to cause the interrupt logic to interrupt the delivery of power when at least one symptom of an islanding condition of the system is detected when the power delivered by the inverter is varied.