A Novel Design Method for a Family of Single-Phase Frequency Estimators Based on Discrete Oscillator for Micro-Grid Application

The family of frequency estimators based on discrete oscillator is believed to be the simplest one for single-phase grid voltage. In order to make this family of frequency estimators more feasible in micro-grid, a novel design is proposed in this paper. The novelty includes a clear input-output relationship for the family of frequency estimators based on discrete oscillator, an optimized design of discrete oscillator model (DOM) and an enhanced pre-filter. Firstly, the input-output relationship is established by the time-domain feedback analysis, and it reveals the frequency estimators have the inherent complex-coefficient comb filtering ability. Then an optimized DOM design is given and it makes the frequency estimators have high filtering ability near the nominal frequency. Lastly, an enhanced pre-filter is proposed to match this optimized DOM for high filtering ability in a wide frequency range. The proposed design method does not bring any stability problems, and also has very low computational burden. Compared with the previous methods, the proposed method has higher frequency estimation accuracy and similar response speed in micro-grid with large frequency fluctuation and harmonic pollution, which is verified by experimental results.