Power quality and stability analysis of large‐scale grid‐connected photovoltaic system considering non‐linear effects

Abstract

This study proposes to incorporate the non-linear factors, such as dead time and phase-locked loop (PLL), into the impedance model of large-scale grid-connected photovoltaic (PV) system and investigates their influence on the system power quality and stability considering the variation of PV capacity. The fundamental component of dead-time voltage can influence the inverter output impedance. The harmonics also have a vital effect on system power quality, especially when the inverter output admittance matches with the grid admittance. The increase of PV capacity can lower the influence of dead time on system phase margin, but may cause serious magnification of certain dead-time harmonics. PLL can make the system asymmetric and brings about the frequency coupling effect. The complex vectors and the transfer function matrix are used to convert the model of PLL from dq - to αβ -axis. The generalised Nyquist stability criterion is utilised to analyse the system stability. The variations of controller parameters in PLL can make the system oscillate. The increase of PV capacity may intensify this effect. Even the stable controller parameters are adopted, large PV capacity can trigger the system oscillation. Finally, the correctness of the theory is verified by simulation analysis and experiment.