Anti-islanding method and apparatus for distributed power generation

An anti-islanding apparatus for isolating a power source from a failed electrical grid, comprising:

• a power converter connectable between said power source and said grid;
• a means for measuring a frequency of said grid;
• a means for calculating a frequency trend in said grid frequency using a present grid frequency measurements and a prior grid frequency measurement;
• a means for calculating a positive feedback power converter control signal based on said frequency trend;
• a control circuit connected to said power converter, wherein said control circuit applies said control signal to said power converter;
• and
• a means of disconnecting said apparatus from said grid when said present grid frequency is outside pre-defined limits.

A method of preventing islanding of a power source on a distributed grid comprising the steps:

• measuring grid voltage;
• calculating a voltage trend in said grid voltage, using a present grid voltage measurement and a prior grid voltage measurement;
• calculating a power converter control signal in a same direction as said voltage trend;
• applying said power converter control signal to said power converter;
• and disconnecting said power source when said present grid voltage measurement is outside acceptable limits.

A method of preventing islanding of a power source on a distributed grid comprising the steps:

• measuring grid frequency;
• calculating a frequency trend in said grid frequency, using a present grid frequency
• measurement and a prior grid frequency measurement;
• calculating a power converter control signal in a same direction as said frequency trend;
• applying said control signal to said power converter;
• and disconnecting said power source when said present grid frequency measurement is outside acceptable limits.