Robust Delay Compensation Strategy for LCL-Type Grid-Connected Inverter in Weak Grid

Capacitor-current-feedback active damping has been widely adopted in digitally controlled LCL-type grid-connected inverters (GCIs). However, their digital control delay causes the system stability to deteriorate within a negative range. Particularly, weak grid, such GCIs are prone be unstable against grid impedance variation. To address above problem, compensation strategy is proposed for an GCI, which second-order low-pass filter (LPF) inserted into capacitor-current-feedback path. This increases virtual-positive-resistance-region from one-sixth of sampling frequency almost Nyquist frequency. Therefore, robustness inverter can significantly enhanced Furthermore, ensure and improve injecting current tracking performance, proportional complex integral (PCI) adopted. More specifically, analysis conducted under discrete domain. Finally, 2-kW prototype constructed, experimental results confirm effectiveness theoretical expectations.