A Fast Response Fault Current Limiter for Flexible DC System
Yuan Jiaxin1,2, Liu Yuxi1,2, Zhou Hang1,2, Liu Jiajia1,2, Li Xuzhe1,2
1. State Key Laboratory of Power Grid Environmental Protection Wuhan University Wuhan 430072 China; 2. School of Electrical Engineering and Automation Wuhan University Wuhan 430072 China
Abstract：In flexible DC transmission systems, the large-scale integration of a high proportion of renewable energy sources sharply increases the grid short-circuit capacity. The system exhibits low inertia, resulting in fault currents that rise extremely rapidly and pose a severe threat to equipment safety. However, traditional fault-current-limiting methods, primarily using smoothing reactors, generally have a fixed inductance. This limitation forces a compromise: a large inductance is required to suppress the steep rise of short-circuit currents, but the same large inductance slows the system's dynamic response during frequent source-load interactions and power-flow fluctuations. Recently, some superconducting or solid-state limiters have been presented, but most suffer from high manufacturing costs, complex control strategies, or an inability to handle bidirectional power-flow reversals effectively. Therefore, this paper proposes a fast response DC fault current limiter (FR-FCL) to accurately distinguish between fault conditions and power-flow adjustments, thereby optimizing the impedance state. Firstly, the topology of the FR-FCL is constructed from two PM-biased iron-core modules connected in a cross configuration within the main current-limiting branch. Hence, regardless of the current direction (positive or negative), one module remains in a deep saturation state while the other automatically desaturates. Secondly, during a short-circuit fault, the surge in current induces a magnetic flux that opposes the PM bias in the working module, causing it to instantaneously exit saturation and enter a high-inductance state. This passive physical characteristic naturally suppresses the rate of rise of fault current without requiring complex detection delays. Thirdly, for scheduled power-flow adjustments, a coordinated control strategy employs an energy-dissipation branch comprising IGBTs and metal-oxide arresters (MOA). Upon receiving a system command to reverse power, this branch is activated, bypassing the main inductive modules. Finally, the current is transferred to the low-impedance path, allowing the system to track the reference power value rapidly. In this integrated model, the combination of passive magnetic limiting and active electronic bypassing addresses the trade-off between fault suppression and dynamic response. Accordingly, the energy-dissipation requirements for the DC circuit breaker (DCB) are significantly reduced. Simulation results on a multi-terminal MMC-HVDC system show that, under a severe pole-to-pole fault condition, the peak fault current with the proposed FR-FCL is limited to 11.61 kA, 52.3% reduction compared to 24.33 kA with a traditional 50 mH smoothing reactor. As the fault persists, the coordinated operation allows the DCB to isolate the fault within 6ms, reducing the required breaking capacity and lowering the overall protection cost by approximately 3.18 million CNY. During power-flow adjustments in the simulation, the system with FR-FCL reaches a stable state within 0.15 s, whereas a traditional reactor requires 0.26 s due to magnetic energy storage. Experimental results from a scaled-down prototype further validate these findings. In the power flow adjustment test, the FR-FCL's response time is less than 1ms, drastically faster than the 5ms observed with the reactor. Furthermore, the prototype effectively limited the fault current to 3.24 A, compared with 11.63 A in the benchmark test. The following conclusions can be drawn. (1) Compared with traditional smoothing reactors, the proposed FR-FCL significantly enhances the fault current limiting capability by over 50% and reduces the stress and cost associated with DC circuit breakers. (2) The proposed model utilizes a cross-connected topology that enables effective bidirectional fault handling without the risk of PM demagnetization, making it more practical than single-direction saturation limiters. (3) The integrated control strategy allows the device to bypass its inductance during normal power flow regulation, achieving a rapid response time (<1 ms) that meets the flexibility requirements of modern rich renewable DC grids.
袁佳歆, 刘宇西, 周航, 刘嘉佳, 李旭哲. 一种快速响应型柔性直流故障限流器[J]. 电工技术学报, 2026, 41(14): 4933-4946.
Yuan Jiaxin, Liu Yuxi, Zhou Hang, Liu Jiajia, Li Xuzhe. A Fast Response Fault Current Limiter for Flexible DC System. Transactions of China Electrotechnical Society, 2026, 41(14): 4933-4946.
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2026, Vol. 41 
