A Virtual Converter Control Scheme Achieving Fast Fault Current Injection With Minimal Impact on Stability in Grid-Following Converters

Abstract

Fast fault current injection (FFCI) is a critical requirement for fault ride-through compliance in voltage source converters (VSCs). A common approach to improving fault current response speed involves increasing the phase-locked loop bandwidth, however, this can significantly compromise system stability. Thus, achieving enhanced FFCI performance without stability degradation remains a major challenge. This paper proposes a FFCI-virtual converter system (FFCI-VCS) control scheme, based on a virtual converter integrated with a virtual impedance network. The proposed method improves the rise time and magnitude of the fault current, enabling fast fault current injection within the first cycle (20 ms) of a grid fault, while maintaining flexible steady-state tracking of the current reference and minimizing the impact on system stability. The system's sequence impedance is analytically modelled and validated using Simulink simulations, demonstrating that stability remains unaffected under specific parameter settings. Simulation results showing the impact of the FFC-VCS on distance protection is presented to demonstrate how it can improve protection performance efficacy. Furthermore, hardware experiments verify the real-time performance of the proposed FFCI-VCS.