A novel design method for a family of single-phase frequency estimators based on discrete oscillator for micro-grid application.

• A clear input–output relationship for the family of frequency estimators is derived based on time-domain feedback analysis. It is revealed that the family of frequency estimators possesses inherent complex-coefficient comb filtering ability. The essential difference of all frequency estimators based on discrete oscillator can be obtained through the established input–output relationship. • An optimized DOM is further derived from the perspective of designing a complex-coefficient comb filter, which makes the frequency estimators have a high harmonic filtering ability near the nominal frequency. This design is simple and easy to understand because the filtering ability of DOM can be analytically expressed by the complex-coefficient comb filter. • An enhanced pre-filter is proposed to expand the frequency range. Different from cascading the same FIR filters at the nominal frequency in previous works, the enhanced pre-filter is tuned at different frequency for simpler digital implementation and flatter attenuation across a wide frequency range. 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. [ABSTRACT FROM AUTHOR]