Reduced-Order Multi-Subsystems of Power Systems with Grid-Following and Grid-Forming Converters for Small-Signal Stability Analysis

The continuous integration of power electronics converters (PECs) based renewable energy leads to unknown stability issues. The well adopted analysis pertaining to the small signal stability of the system incorporating grid-following (GFL) and grid-forming (GFM) PECs is mainly conducted on the two-machine systems, whereas this being applied to large-scale power systems remains inadequate. This paper, thus, introduces the concept of stability-equivalent multi-subsystems (SEMSs) for power systems that integrate heterogeneous PECs with GFL and GFM control schemes. The SEMSs achieve the decoupling of a complicated system into multiple small-signal stability equivalent two-machine subsystems with clear physical meanings. The SEMSs retain the interactions between GFL and GFM PECs, and between PECs and the network. On this basis, the stability characteristics of the original system can be inferred based on the stability analysis of each SEMS. A concomitant concise stability criterion is proposed. The proposed criterion incorporates the characteristics of network and PECs, providing an insight of their independent impact on the overall system stability. This reduces the computational burden of the large-scale systems' stability analysis. Hardware-in-loop (HIL) test results and simulations of a real-world power system verify the effectiveness and applicability of the proposals.