Abstract：When the collection line of the flexible direct current (DC) transmission system of a new energy mega-base experiences a fault, the flexible DC converter station may, due to overcurrent blocking, result in the disconnection of the entire connection to the new energy source. For the existing approach, either setting a threshold for the setting value directly limits the amplitude, but the set threshold will cause a clipping phenomenon on the reference current, which will result in distortion of the output current of the converter in asymmetric faults; Either the current reference value can be proportionally reduced by limiting. This method can cause overcurrent in non fault phases during asymmetric faults, and the output current level of the fault phase is low, which cannot fully utilize the fault current output capability of the converter. There are also methods that suggest that the proposed segmented voltage reduction control method mainly achieves segmented voltage reduction by setting multiple criteria. This method is suitable for asymmetric faults and can achieve current limiting in the steady-state stage, but there are overcurrent problems in the transient stage; Alternatively, the virtual impedance value can be uniquely calculated based on port faults, and the voltage reduction amplitude can be adjusted by combining the current reference value with the degree of exceeding the limit. Due to the large and unique setting value of the virtual impedance in this method, the system voltage may be too low under mild faults. To address these issues, this paper, considering the control characteristics of the new energy grid-connected converter, analyzes the necessity of retaining the voltage outer loop during the low penetration control period of the flexible converter station. Subsequently, a method for low voltage ride through of the collection system is proposed based on sequence current limitation and equivalent impedance. This involves separating the reference currents output by the outer loop into positive and negative sequences, then transforming them into the three-phase coordinate system to achieve independent processing of the output currents for each phase, thus solving the problem of asymmetrical fault transient overcurrent of the faulted phase. Simultaneously, the paper utilizes the equivalent impedance method to adaptively adjust the reference values of the outer loop voltage, avoiding the drawback of the outer loop control exiting due to saturation after the inner loop current limiting section becomes effective. This helps prevent overcurrent blocking of the flexible DC converter station during the fault steady-state period. The authors constructed a refined model of the AC collection system for the new energy mega-base connected to the flexible converter station in PSCAD and validated the effectiveness of the proposed control method through simulation experiments.
刘昊霖, 贾科, 毕天姝, 钮厚敏, 李伟涛. 接入新能源大基地汇集系统的柔直换流站低电压穿越方法[J]. 电工技术学报, 2025, 40(3): 759-770.
Liu Haolin, Jia Ke, Bi Tianshu, Niu Houmin, Li Weitao. Low Voltage Ride Through Methods for Flexible DC Converter Stations Connected to the Gathering System of New Energy Base. Transactions of China Electrotechnical Society, 2025, 40(3): 759-770.
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2025, Vol. 40 
