Evaluation of the Sub-Synchronous Control Interaction Based on the Elastic Energy Equivalent System

This paper proposes an Elastic Energy Equivalent System (EEES) for analyzing the sub-synchronous control interaction (SSCI) in the power system integrated with power electronic converters. The EEES can analyze the energy interaction between the series compensation and the converters' controller, and quantitatively assess the impact on SSCI induced by the converters' controller from the view of elastic energy. First, inspired by the vibration process of a spring-damper system, we establish the EEES to imitate the electromagnetic oscillation, so as to explore the SSCI phenomenon in power systems by analyzing the energy composition of EEES. Then, an equivalent damper of EEES is used to model the controllable dissipated energy of the converters' controller, so a criterion can be developed to evaluate the damping effect for stabilizing the system. Finally, the effectiveness of the proposed EEES is validated on a power system integrated with the doubly-fed induction generator controlled by the virtual synchronous generator. The results demonstrate that the virtual synchronous generator can provide positive damping to the SSCI under specific sub-synchronous frequencies. However, this positive damping is limited due to the noticeable negative damping effect on SSCI induced by the rotor-side converter controller.