Abstract：With the increasing penetration of large-scale renewable energy generation, the synchronization stability of grid-forming (GFM) converters exerts a profound influence on power system transient stability. When the system encounters large disturbances, such as severe voltage sags, significant load variations, and metallic ground faults, the converter current will increase significantly. It threatens the safe operation of power electronic devices and can lead to large-scale tripping of converter-based power sources. Therefore, effective fault current limiting control is one of the key measures to ensure the stable operation of GFM converters. However, conventional current limiting control strategies commonly reduce the equivalent deceleration area of GFM converters, thereby decreasing the transient stability margin. This paper proposes a novel fault current limiting strategy for converters based on improved funnel control (IFC). The main contributions of this paper can be summarized as follows. The equivalent model of the GFM converter under significant disturbance is established, and the adverse effect of the current saturation algorithm (CSA) is revealed through the analysis of power angle stability. It is found that the introduction of CSA reduces the deceleration area of the GFM converters during significant disturbances. Moreover, simulation results indicate that overcurrent would occur during the fault when the virtual resistor (VR)-based current limiting strategy is adopted. Considering that the funnel control scheme can accurately track the reference value of the objective variable and the tracking error can be flexibly controlled, the IFC current limiting strategy achieved by utilizing switching logic is designed, which can restrict the fault current amplitude within the pre-defined error funnels. The relative degree in the single-input single-output (SISO) system established by the circuit formulation of the converter is obtained, making it feasible to use a first-order funnel controller for direct fault current regulation due to the first-order relative degree. Moreover, a switch strategy is also designed for recognizing the overcurrent and the voltage recovery. The converter switches to IFC current limiting mode when the overcurrent appears and switches back to GFM control mode after the grid voltage recovers. To ensure the converter is protected from the hazards of constant faults, the proposed control strategy is capable of issuing a converter shutdown command after identifying long-term faults. Furthermore, the boundedness of the tracking error is proved by theoretical analysis. Single-phase output currents are investigated by simulations on Matlab/Simulink with different fault current reference values. IFC, CSA, and VR current limiting methods are compared by hardware-in-the-loop (HIL) experiments under symmetrical and asymmetrical faults. The following conclusions are obtained. (1) Compared with the CSA and VR current limiting algorithms, the proposed IFC strategy shows superior current limiting performance. On one hand, it does not affect the transient stability ability of the system. On the other hand, this algorithm has an adjustable current limiting amplitude from 0.8(pu) to 1.1(pu), which can ensure that the system maintains stable operation during faults. (2) The proposed strategy can suppress the asymmetric fault current without injecting negative sequence current and maintain three-phase symmetrical operation despite the asymmetric fault. Meanwhile, the implementation of the IFC algorithm is simple and requires no changes to the existing controller structure.
李昊恒, 刘洋, 武艳秋, 陈金聪. 一种基于改进漏斗控制的构网型换流器故障电流限制策略[J]. 电工技术学报, 2026, 41(6): 2045-2058.
Li Haoheng, Liu Yang, Wu Yanqiu, Chen Jincong. A Fault Current Limiting Strategy for Grid-Forming Converters Based on Improved Funnel Control. Transactions of China Electrotechnical Society, 2026, 41(6): 2045-2058.
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