Stability Region Estimation and Decentralized Transient Control for Parallel Grid-Tied Grid-Forming Inverters

Renewable energyes are highly penetrated in power system through Grid-forming inverter (GFMI). Transient stability of single GFMI system under severe grid fault has been thoroughly analyzed in recent years, but quantitative analysis for parallel grid-tied GFMI system is rarely studied. To fill this gap, the large signal equivalent model of parallel system considering the interaction between inverters is newly built. Based on the model, the Lyapunov function incorporating kinetic energy, potential energy, damping dissipation, and interaction energy is constructed for accurate stability region estimation. Then, the effect of control parameters on stability region is analyzed, indicating that increasing damping, reducing inertia, and lowering reference power of one GFMI can deteriorate stability margin of parallel GFMI system due to the enlarged interaction power, which is distinct from single GFMI system. For this, a decentralized transient control that adaptively adjusts damping, inertia, and reference power is proposed to guarantee transient stability and achieve low-voltage ride-through (LVRT) for parallel system without relying on communication, system information. Finally, simulation and experimental tests validate the correctness of theoretical analysis and the effectiveness of proposed control.