Nonlinear Stability Analysis and Active Compensation of a Utility-Scale Single-Stage Grid-Connected PV System

This paper presents a comprehensive nonlinear stability analysis and active compensation method for a utility-scale single-stage grid-connected photovoltaic (PV) system. First, a describing function (DF)-based stability analysis is conducted considering the nonlinear dynamics of the incremental conductance (INC)-based maximum power point tracking (MPPT) algorithm and the effects of the PV generator operating point changes. Next, the analysis characterizes the impact of the MPPT sampling time and perturbation step size on oscillation magnitude and frequency. The study showed that a shorter sampling time and larger step size result in a faster response. However, an increase in the step size increases the oscillation magnitude; the latter does not change with the step size. Then, considering the INC-based MPPT nonlinear dynamics, the overall system’s damping and oscillatory modes are characterized under different photovoltaic generator operating conditions and system parameters using the DF method. The study showed that the system stability is reduced when the photovoltaic generator operating point moves to the left of the maximum power point and with the reduction of the dc-link capacitance and ac-side filter inductance. Therefore, an active compensation method is proposed to reduce the oscillations and improve the stability and dynamic performance at different operating conditions and in the presence of the MPPT nonlinear dynamics. Finally, detailed nonlinear time-domain simulation results are presented to validate the analytical results and the effectiveness of the proposed compensation method under various operating conditions.