Optimal Capacity Configuration of VSM-Controlled Grid-Connected Inverters in a Multi-Inverter System Based on Hybrid-Mode Control Under Weak Grids

With the increasing penetration of renewable energy generation, the power grid shows weak grid characteristics, which seriously affect the stability of grid-connected inverters. For grid-connected inverters, there are two basic control modes: current source mode (CSM) and voltage source mode (VSM), also known as grid-following control and grid-forming control. Existing studies show that the CSM-controlled grid-connected inverters can operate stably under the strong grid, while the system stability margin decreases or even becomes unstable under the weak grid. The VSM-controlled grid-connected inverters are just the opposite. Some literature proposes a hybrid-mode control for the multi-inverter system under weak grids: the system contains both CSM-controlled grid-connected inverters and VSM-controlled grid-connected inverters, thus effectively improving the overall stability of the system. However, the existing literature does not quantify the capacity of the VSM-controlled grid-connected inverters in this system. Therefore, a stability analysis based on multi-performance-index constraints, such as stability margin and control bandwidth, is conducted for this hybrid-mode controlled system, and the optimal capacity configuration of VSM-controlled grid-connected inverters is obtained in this paper. Finally, the experimental results prove the correctness of the analysis.