Comparison of Fault Ride-Through and Fast Fault Current Injection Capabilities of Grid-Forming Converters With Different Control Strategies

Grid-forming (GFM) converters possess advantages in stabilizing the grid compared with the commonly used grid-following (GFL) converters in the modern power system. Various control strategies for GFM converters under normal operating conditions have been proposed and well-studied. However, research on their Fault Ride Through (FRT) capabilities and Fast Fault Current Injection (FFCI) abilities under fault conditions is not yet comprehensive. Issues such as fault current injection, current limitation, increased system complexity, and difficulty handling unbalanced faults are noteworthy shortcomings. Existing control strategies addressing these issues for GFM converters during ac faults primarily fall into two categories: 1) Switched Operation to GFL mode during faults (SOGFL), and 2) the use of additional auxiliary current-limiting (ACL) control loops. This paper models these two representative control approaches and compares their FRT and FFCI performance by analyzing their transient responses under both balanced and unbalanced fault scenarios using Simulink. The SOGFL approach demonstrates the flexibility of current injection but requires switching operation mode and faces related challenges, such as extended recovery time and increased system complexity. The ACL approach has a relatively simple structure and low sensitivity requirements for fault detection, however, it offers limited current injection flexibility and constrained capabilities to adjust to different grid requirements.