Effects of Nonlinear MPPT Control and PV Array on Stability Analysis for a Utility-Scale PV Energy System

Various studies have focused on the stability analysis of PV energy systems. However, the majority of these methods rely on a linearized model around an equilibrium point, which cannot exactly reveal the influence of the nonlinear power controller and PV array on the PV energy system at low frequencies. To conquer this gap, this article contributes to providing intuitive insight into stability analysis and establishing a complete system model including the PV panel, boost converter, DC line, central inverter and AC grid. The describing function (DF) of the nonlinear discontinuous element in PV and the transfer function of the linear elements in the system are derived to determine the system stability. To support the stability hypothesis based on the DF-based stability analysis method, a comparative study in contrast to existing stability analysis methods is provided. The impedance-based method may not be accurate when the division of the 'source-load' subsystem is different. The proposed DF method can offer further concluding remarks on MPPT control, the number of PV panels, DC/DC converter, etc. Based on a hardware-in-the-loop (HIL) operation, the proposed model is explicitly validated under different constraints, and the influence of control and circuit parameters on system stability are illustrated.