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Pre‐filter phase‐locked loop: principles and effects with inter‐harmonic perturbation

The phase-locked loop (PLL) is an available synchronisation technique that can extract the fundamental frequency and phase of the grid. Benefited from the filter properties, pre-filter PLL is widely applied in voltage source inverters (VSIs) to enhance the accuracy of phase extraction. With the consideration of inter-harmonic perturbation, the principles between pre-filter PLL and VSI performance as well as the effects of pre-filter PLL on VSI are investigated in this study. Based on the conventional PLL, the small signal of pre-filter PLL is proposed. To fully represent the pre-filter PLL effects, the simplified VSI model is established and the current performance of VSI could be presented by the pre-filter PLL. From the angles of current total harmonic distortion, the effects of pre-filter PLL under inter-harmonic perturbation are clarified. The effects of pre-filter PLL on VSI are validated under the inter-harmonic perturbation based on the experiment platform. The results indicate that the current performance of VSI could be improved with the decreased bandwidth of both pre-filter and PLL, which shows a valuable application reference for the optimised design of VSI.