The Propagation of VSC Damping Effect to Exploit AC Transmission Limit

Abstract

In this paper, the propagation of active damping and its implication of sizing a VSC stabilizer in AC transmission is investigated. In the context of PLL-based grid-following Voltage Source Converter (VSC) based AC transmission, the enabling design of stabilizer to exploit transmission limit of active power is presented. After analyzing the boundary of active transmission from VSC side, the effect is showcased by EMT time domain simulations, which reflects the coupling effect between the reach of effect and the magnitude of transient response. With frequency domain analysis, it reveals that the effect of stabilization diminishes when electrical distance from the stabilizer grows, whereas the required size of VSC stabilizer to withstand the transient current decreases. It is found that transient response of VSC stabilizer can be approximated with small signal impedance with the large-signal voltage angle corrected. This principle is numerically verified with time domain simulations. As an implication, this paper once again proves that PLL-based grid-following VSC is not fundamentally flawed in a low-SCR grid.