Impact of VSC-ESS with VSG control on SSR of nearby synchronous machine

Traditional methods for power system analysis and control are facing more and more challenges with the increasing penetration of systems containing VSCs (voltage source converters, e.g. high voltage DC transmission systems, PV or wind farms). Considering the difference between VSCs and synchronous generators, researchers have proposed a control scheme named virtual synchronous generator (VSG) to emulate the inertial characteristics of a real synchronous machine (SM) to tackle the problem of frequency stability. When disturbances occur in the system, VSGs may exhibit oscillatory behaviors in the same way as real SMs, while it also has interaction with SMs due to power exchange as well as frequency and angle synchronization. Under this circumstance, how the existence of VSGs influences subsynchronous resonance (SSR) becomes an important issue. Based on the equivalence theorem, this article focuses on the impact on SSR of a VSG interconnected with a multi-mass SM. After a VSG being equivalently integrated into the SM, it is evident that there are changes of the equivalent inertia and armature impedances, both of which affect the behaviors of the oscillation as a result.