Stability Improvement of an LCL-based Photovoltaic Power Conditioning System Connected to Weak Network Using Capacitor Voltage Feedforward Compensation

In this paper, the performance of a weak-grid-connected photovoltaic power conditioning system with an LCL filter is investigated. Inverter-side current feedback and capacitor voltage feed-forward are used to control the grid-connected inverter, which requires only two sensors and has lower complexity. The use of digital control in conjunction with the conventional strategy results in an inverse resonance phenomenon within the loop gain, ultimately leading to system instability. To address this issue, a phase compensator is introduced in the capacitor voltage feed-forward path to maintain the stability of the LCL-filter-based photovoltaic power conditioning system against variations in weak grid impedance. The parameters of this compensator have been selected through a precise analysis to ensure the proper performance of the system. A sensitivity analysis has been conducted for the LCL filter parameters, which demonstrates the high reliability of the proposed system. The proposed method has been compared to existing methods in terms of the passive performance of the grid-connected inverter. Under the conventional strategy, the grid current THD is ۶.۲۲%, whereas the proposed strategy reduces it to ۱.۴۲%. The simulation of the proposed system is carried out in the Simulink environment of MATLAB, and the results demonstrate correct operation of the proposed system in terms of maximum power point tracking, maintaining system stability in a weak grid, and ensuring high quality of the current injected into the grid. The maximum power of the solar array is ۴۵۸۱ W at an irradiance of ۱۰۰۰ W/m² and ۳۶۲۹ W at an irradiance of ۸۰۰ W/m².