The use of digital phase locked loops for estimation of instantaneous frequency rate in distributed power networks

A power system disturbance scenario which is of particular interest is that which occurs when one or more generators in a distributed power system is ´taken out´. Under such circumstances the load becomes especially great on the remaining generators and the speed of rotation will rapidly decrease changing the frequency of a mains signal. Fast and accurate instantaneous frequency rate (IFR) estimation algorithms are used for disturbance detection, to allow enough time for introduction of appropriate control measures that will prevent system failure. The main application would be in the load shedding scheme. Some recent work has suggested estimating the IFR by use of the ambiguity function and cubic phase function algorithms. The method presented in this paper estimates instantaneous frequency drifts with the use of digital phase locked loop (DPLL). Simulations show that DPLL based methods can estimate the IFR with a lower mean square error (MSE) than existing maximisation methods.