基于电压与电流强度的跟网型/构网型混合系统小信号稳定性评估与增强

With the rapid development of renewable energy, power systems are witnessing an increasing penetration of power converters. Currently, converters widely employ grid-following (GFL) control, while grid-forming (GFM) control is considered as a grid-friendly strategy to accommodate large-scale power converters. Hence, GFL-GFM hybrid systems (GGHSs) will prevail in the future. However, such systems may encounter small-signal stability issues across a wide frequency range due to the closed-loop interactions among the power network, GFL, and GFM converters. To address this problem, this paper first introduces the concept of grid current strength, a metric that quantitatively characterizes the stability of GFM converters, thereby extending the traditional grid voltage strength. We derive low-dimensional GFL and GFM subsystems to represent the dynamics and stability of the original high-dimensional system. On this basis, a two-dimensional strength index is proposed to quantitatively assess the stability margin of the GGHSs in a tractable manner. Based on this index, we analyze the impact of the proportions of GFL and GFM converters on system stability and demonstrate that inappropriate proportions may lead to instability. Finally, we propose a method to rapidly identify the critical GFL or GFM devices that dominate the system stability using participation factors. On this basis, we introduce stability enhancement strategies for GGHSs in both the system planning and system operational stages. The efficacy of the proposed assessment and enhancement methods is validated through time-domain simulations and hardware-in-the-loop (HIL) tests.