Improved phase-locked loop-based control for grid-integrated PV system

This work presents an improved phase-locked loop (IPLL)-based control for grid-integrated photovoltaic (PV) system (GIPVS). It is used to extract amplitude, frequency, and phase angle of distorted load currents to control PV-grid-interfaced voltage source converter (VSC). The VSC controls active and reactive powers at unbalances and distortions in the grid voltages. The control algorithm of VSC includes power feed-forward term, DC-link voltage, and grid voltages. The feed-forward term improves the dynamic performance of a GIPVS and enhances the utilisation of VSC. Three-phase IPLLs extract the in-phase components of three-phase load currents at utility frequency. Further, these in-phase components of load currents are used for estimation of reference-grid currents. The proposed IPLL-based control algorithm offers good dynamic response even under unbalanced load condition. The efficient working of IPLL-based control algorithm is realised by extracting maximum power from PV-grid system and through its power-quality improvement. The perturb and observe (P & O) control algorithm is used for optimum utilisation of a PV array. A developed prototype of PV-grid system is used to implement an IPLL-based control algorithm under different operating conditions.