PLL performance under frequency fluctuation-compliance with standards for distributed generation connected to the grid

Grid frequency fluctuation from the nominal value is expected by the standards related to distributed generation (DG) and smart grid (SG) systems. The Phase Locked Loop (PLL) estimates a signal synchronized with the fundamental frequency of the grid voltage that will be used by the controllers of the power converter of a DG system. A discrete model for the PLL, including the phase detector harmonic generation, is proposed. Poor low pass filtering of the PLL phase detector output signal can lead to PLL output distortion and slow time response. This paper analyses and compares the operation of moving average (MAV) filters, and two strategies of adaptive MAV filters, proposed in the literature, under frequency variation. The PLL controller and its tuning presented in these papers are also discussed. An improved PLL based on adaptive MAV filter and a better tuned controller is presented. Simulation and experimental results are provided.