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 the discrete oscillator, an optimized design of the 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 that the frequency estimators inherently possess complex-coefficient comb filtering ability. Then, an optimized DOM design is presented to enhance the frequency estimators' 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 has no stability issues and a very low computational burden. Compared with previous methods, the proposed method demonstrates higher accuracy in frequency estimation and similar response speed in micro-grid with significant frequency fluctuation and harmonic pollution, verified by experimental results.