Research on Control Strategies for LCL-Type Grid-Connected Inverters

As the share of renewable energy generation systems in power grids increases, grids are exhibiting weak or even extremely weak grid characteristics, posing severe challenges to the stable and efficient operation of renewable energy grid-connected generation systems. In weak grids, harmonic voltages at the point of common coupling (PCC) and grid impedance cannot be ignored. LCL grid-connected inverters may experience resonant frequency shifts due to grid impedance variations, and harmonic voltages can affect voltage feedforward control. To address these issues, an active damping control method using a negative first-order low-pass filter for capacitor current is proposed to enhance the adaptability of LCL grid-connected inverters under varying grid impedance. This method improves system static performance without compromising stability. MATLAB simulations demonstrate its effectiveness.