Reconfigured passivity-based control strategy of LCL-type grid-connected inverter under complex grid conditions

LCL-type grid-connected inverters have seen extensive use of the passivity-based control (PBC) system. However, traditional PBC systems rarely take time delay into account while designing the system or doing a stability study. Therefore, utilizing Lyapunov's criterion to conclude that the system is stable is not accurate. The analysis revealed that the differential terms of PBC loops with the Euler-Lagrange (EL) mathematical model could induce instability considered control delay for LCL-type grid-connected inverter system. Compared with traditional EL-PBC method, this paper proposed a reconstructed EL-PBC scheme by properly optimizing the noise term. Then, the equivalent output impedance of the grid-connected inverter system with proposed controller is analyzed with frequency domain passivity theory. The controller parameters are also optimized to ensure both the internal stability of LCL-type grid-connected inverter and the risk of interactive resonance in complex weak and nonideal grid. Results from simulation and experimentation support the modified control structure's efficacy and performance.