A Robust Three-Phase Pre-Filtered Phase Locked-Loop for the Sub-Cycle Estimation of Fundamental Parameters

This paper shows a proposal for a non-adaptive pre-filter based three-phase type-I synchronous reference frame-based phase locked-loop (PLL) algorithm. This solution is simpler than the widely accepted type-II PLL algorithms, which require a great deal of effort as regards tuning the proportional-integral gains. In the proposed approach, a type-I controller that is merely a proportional gain with a fixed magnitude is employed. Moreover, improvements are made to the implementation of the non-adaptive demodulation based pre-filtering approach, which consist of moving average filters and delayed signal cancellation operators. In the event of a fault, the improved pre-filter structure is still incapable of rejecting the fundamental negative sequence (FNS) component. We propose to overcome this issue by using a non-adaptive computationally simplified structure to improve the immunity to the adverse effects of FNS. It is consequently possible to avoid the dependence on the frequency feedback loop while involving a simple and fast feed-forward error compensation approach. Finally, the performance of the proposed PLL is experimentally verified using a real time controller to demonstrate its feasibility for grid synchronisation applications.