A Coordinated Current Limiting Method for Flexible DC Grids Based on Source-Grid Limiting Contribution

Fault current limiting plays a crucial role in maintaining the safe operation of flexible DC grids. Nevertheless, existing fault current limiting techniques often focus on individual limiting devices, with few strategies tailored to coordinate with specific fault conditions. To maximize the effectiveness of current limiting devices, prevent converter station lockout, and reduce the fault interruption capacity of DC circuit breakers (DCCBs), this paper proposes an adaptive source-grid coordinated current limiting method based on limiting contribution in flexible DC grids. This method integrates the current limiting principles and objectives of modular multilevel converters (MMC) and introduces a control logic between quantitative indicators and MMC modulation coefficients to develop a source-side adaptive current suppression control method for flexible DC grids. For the coordinated method between source-side MMC and grid-side fault current limiters (FCL), the principle of “grid-side priority, source-side supplementation” is introduced to enhance the performance of the coordinated current limiting approach. Finally, a four-terminal flexible DC grid simulation was established using the PSCAD/EMTDC platform to validate its validity across a range of fault conditions.