Patent Number: 6,298,309

Title: Current based frequency tracking method and apparatus

Abstract: A method for measuring a fundamental frequency of a power system comprisessampling voltage and current waveforms associated with the power system,wherein the voltage and current waveforms are characterized by afundamental frequency component that may vary over time. Next, determinewhether, according to a prescribed frequency tracking criterion, a presentvalue of the fundamental frequency can be measured using voltage samples.If so, measure the fundamental frequency using the voltage samples, andset a best available value ("freq") equal to the measured value based onvoltage samples. If the fundamental frequency cannot be measured using thevoltage samples, determine whether, according to the prescribed frequencytracking criterion, the present value of the fundamental frequency can bemeasured using current samples. If so, measure the fundamental frequencyusing the current samples and set the best available value equal to themeasured value based on current samples. If the present value of thefundamental frequency cannot be measured using the voltage or currentsamples, determine whether previously measured values of the fundamentalfrequency based on current are stable according to a prescribed stabilitycriterion and, if so, set the best available value to a value based on thepreviously measured values for a limited period of time.

Inventors: Benco; Joseph (Germansville, PA), Das; Ratan (Allentown, PA), Downs; Cliff (Richboro, PA)

Assignee:

International Classification:

Expiration Date: 10/02/2013