Anti-Islanding Systems and Methods Using Harmonics Injected in a Rotation Opposite the Natural Rotation

A system, comprising:

• a) at least one local power source;
• b) at least one power converter, connected to draw power from the local power source and to drive power onto multiple phase lines of a power bus which is at least sometimes connected to a utility power grid;
• wherein the power converter also operates to add in a current component, on the output terminals, at the nth harmonic of the predetermined base frequency, with a distinctive phase sequence which is different from that normally present in the nth harmonic;
• and
• c) control circuitry which monitors the voltage on the multiple phase lines of the power bus, and controls the operation of the power converter accordingly;
• while also testing whether a voltage corresponding to said nth harmonic and said distinctive phase sequence exceeds a threshold value on the output terminals, and, if so, indicating an islanding condition.