Yilan Yu

Inverter-based resources are widely integrated into power systems, which may interact with each other and induce the risk of oscillation. This paper introduces a two-degree-of-freedom elastic energy equivalent system (2DOF-EEES) to assess interactions in power systems integrated with multiple inverter-based resources. Unlike traditional impedance-based analysis, the 2DOF-EEES intuitively represents the interactions between multiple inverters and the power network by constructing an equivalent elastic structure with two degrees of freedom. Initially, by equating parallel RLC circuits to a two-degree-of-freedom spring–damper system, the 2DOF-EEES is established. Subsequently, the 2DOF-EEES for the power system, integrated with multiple inverter-based resources, is developed by deriving analytical expressions for common and differential-mode energy. The effectiveness of this method in accurately assessing the oscillatory stability of the system is validated through time-domain simulation. The results further reveal that the differential-mode energy influences the common-mode energy via the equivalent elastic structure in the 2DOF-EEES, thereby affecting the interaction between the wind farm and the network.

This paper proposes a control strategy of the multi-terminal grid-forming soft open point (MGSOP), aimed to ensure uninterrupted power supply during distribution feeder outages. Unlike existing approaches, the proposed control does not rely on an ideal DC voltage assumption, master-slave structure, or control mode switching. In the MGSOP, the AC-DC and DC-DC converters are used for multi-feeder interconnections and energy storage integration. The MGSOP control system comprises local and coordinating controllers, used to implement the proposed control strategy, which is made up of three sections: 1) Grid-forming AC voltage control implemented by local controllers, which ensures the independent construction of AC voltage and prevents control switching between grid-connected and standalone modes. 2) Hierarchical DC voltage control collaborated by both local and coordinating controllers. Based on the multi dynamic of DC voltage ( $\Delta U_{dc}$ and dU_dc/dt), the control ensures dynamic DC power balance and DC voltage stability, avoiding system instability and restoration failures caused by the shutdown of the master converter under traditional master-slave control. 3) Coordinated control for the power regulation among multiple feeders, which reduces the consumption of energy storage during supply restorations. Finally, the effectiveness of the proposed control strategy is validated by simulations.