Frequency Adaptive Multistage Harmonic Oscillator for Renewable-Based Microgrid Under Nonideal Grid Conditions

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Diurnal and seasonal variability associated with the renewable power generation is disinterested by grid integration. However, for the cases of developing and underdeveloped countries, the utility grids are relatively weak and exacerbate the issues related to power quality, frequency jumps, grid voltage distortion, sag, and swell. To deal with these issues of weak grid-integrated hybrid-renewable-power-generation-based microgrid and to ensure reliable and effective operation, the frequency adaptive multistage harmonic oscillator (MSHO) control is used in this article. This control comprises of multistage filter with dc bias rejection loop and frequency-locked loop. The multistage filter is tuned to dominant lower order harmonic and allows the selective elimination of the harmonics. An MSHO is used for assessing the fundamental constituent from harmonics and dc-bias-infected grid voltage. It also extracts the positive-sequence constituent from distorted/unbalanced grid voltages while maintaining the balanced grid currents. It effectively overcomes the frequency perturbations and nonlinear load compensation and significantly increases the overall reliability and quality of power. A set of back-to-back associated power converters provide a flexible speed operation of the wind power generation system. Different functionality modes are incorporated in order to address round the clock operation of the microgrid, enabling the reactive power compensation capability and mitigation of the harmonics demanded by the nonlinear load connected at the distribution side. The maximum power operating point for both wind and solar photovoltaic arrays is acquired by the individual implementation of the perturb and observe technique. The performance investigation of the system is carried out on a developed laboratory prototype. The aptness and the functionality of the control algorithms are noticeable from the experimental results. The issues of loss of supply, estimation of grid voltage signal, effects of weak grid, variability of renewables with curtailable load are addressed, and the power quality standard IEEE-519-2014 is satisfied.