A Two-Degree-of-Freedom Elastic Energy Equivalent System for Evaluating Interactions in Power Systems With Multiple DFIG-Based Wind Farms

Abstract

This paper proposes a two-degree-of-freedom elastic energy equivalent system (2DOF-EEES) to assess the sub-synchronous control interactions in the series compensated network integrated with multiple doubly-fed induction generator (DFIG)-based wind farms. Unlike traditional impedance-based aggregation approaches, the proposed 2DOF-EEES employs a two-degree-of-freedom elastic structure to intuitively characterize interactions between wind farms and the power network. Initially, the 2DOF-EEES is derived through an analogy between parallel RLC circuits and a two-degree-of-freedom spring-damper system, enabling a mechanical interpretation of oscillatory interactions. Subsequently, the 2DOF-EEES for power systems with multiple DFIG-based wind farms is developed by deriving its analytical expressions of common and differential-mode energy. Finally, integrating the analytical expressions of the 2DOF-EEES and the measured oscillatory information, the oscillatory stability and the damping distribution of the wind power systems are evaluated online. The results further demonstrate that the differential-mode energy influences common-mode energy via the equivalent elastic structure in the 2DOF-EEES, thereby affecting the interaction between the wind farms and the network.