Evaluation of grid-forming converter's impact on distance protection performance

Motivated by the net-zero carbon emission target, the GB transmission system has seen a massive increase in the amount of Converter Based Resources (CBRs). Grid-Forming Converters (GFMs) have attracted significant interests for supporting the future system operability with high penetration of renewables due to their various more desirable properties compared with Grid-Following Converters (GFLs), e.g., stronger capability to operate in weak grids. Recent research work has found that Fault-Ride Through (FRT) strategies of CBRs have significant impact on the distance protection performance, and comprised protection operation was observed when synchronous generation sources were replaced with CBRs. However, existing research work has mainly focused on the impact of the GFLs' FRT on distance protection, while the impact of GFMs, which could have very different FRT strategies, has not been comprehensively investigated. In this paper, a GFM with two typically used FRT implementations, i.e., the current control based FRT and the virtual impedance based FRT, is developed in the Real-Time Digital Simulator (RTDS) and the impact of the two FRT methods on distance protection is investigated for both balanced and unbalanced fault conditions. By comparing the relay performance with two FRT strategies, it is found that the distance protection appears to have better performance in terms of faulty phase selection, accurate impedance measurement and impedance measurement stability when the virtual impedance-based FRT is adopted by the GFM.