Fault Ride-Through Control Method for VSC-HVDC Balancing between DC Voltage Security and Reactive Power Support
Ouyang Jinxin1, Chen Jiyu1, Li Ang1, Chen Yujie1, Xiao Chao2
1. State Key Laboratory of Power Transmission Equipment Technology Chongqing University Chongqing 400044 China; 2. Electric Power Research Institute of State Grid Henan Electric Power Company Zhengzhou 450052 China
Abstract：Voltage source converter-based high voltage direct current (VSC-HVDC) is essential for building modern power systems. The rapid rise of DC voltage under the three-phase fault in the receiving-end grid may trigger overvoltage blocking and threaten grid stability. The existing fault ride-through method based on the dynamic braking resistor (DBR) for VSC-HVDC uses DC voltage as the activation condition. It does not take into account the impact of the AC bus voltage and reactive power of the receiving-end converter (REC) on DC voltage security, which may lead to non-essential activation of DBR due to unreasonable activation conditions or excessive reactive power of REC, causing extra shocks to the AC-DC system and increasing energy dissipation. According to Davina's theorem, the faulty receiving-end grid is equated to a two-port network. Among them, the ideal voltage source and series impedance are the equivalent potential and the equivalent impedance of the receiving-end grid during normal operation, respectively. The parallel equivalent fault transition impedance is used to equate the effect of a short-circuited branch circuit on the equivalent impedance of the receiving-end grid. The analytical equations of the DC voltage and AC bus voltage of REC concerning the active and reactive power of REC are deduced. The power feasible domain of REC under the limitation of the maximum permissible AC current with the guarantee of DC voltage security is established to depict the power control capability of REC under the receiving-end grid fault. The minimum active power of REC that precisely guarantees DC voltage security increases with the increase in fault duration, and the range of active and reactive power of REC under the limitation of the maximum permissible AC current is constant, so that the power feasible domain of REC exhibits a shrinking characteristic. If the power feasible domain of REC under a certain fault duration has only one point, the fault duration is the critical clearing time of the receiving-end grid fault. Since REC can provide the maximum active power under the limitation of the maximum permissible AC current, the DC voltage will exceed its maximum permissible value at the critical clearing time. Therefore, the critical clearing time characterizes the security margin of the DC voltage under the receiving-end grid fault. The active current of REC required to maintain DC voltage stabilization cannot be increased without limit as the degree of AC bus voltage drop increases. The control reference value of REC shall be adapted to the different fault severities in the receiving-end grid. Suppose REC can provide a certain reactive current while restoring its active power to its initial value before the fault. In that case, the DC voltage can be kept stable, and REC can continue to use constant DC voltage control. When the receiving-end grid fault is more severe and the active power decreases due to the reactive power provided by REC, the DC voltage will continue to rise with the increase in fault duration. REC should be switched to the fixed active and reactive power control and cooperate with DBR. The coordination control point is the operating point of REC that can withstand the power imbalance for the longest time. The time required for DC overvoltage can be maximized when REC is operated at the coordination control point. If the critical clearing time exceeds the fault duration, the DC voltage during the receiving-end grid fault is less than the maximum permissible DC voltage. If the fault duration exceeds the critical clearing time, the unbalanced power is minimized, and the energy dissipated to ensure DC voltage security is minimized. Therefore, no matter how long the fault duration is, when the AC bus voltage of REC is lower than the switching threshold voltage, REC should be controlled to operate at the coordination control point and activate DBR according to the critical clearing time.
欧阳金鑫, 陈纪宇, 李昂, 陈宇捷, 肖超. 兼顾直流电压安全与无功支撑的柔性直流输电故障穿越控制[J]. 电工技术学报, 2024, 39(19): 6129-6144.
Ouyang Jinxin, Chen Jiyu, Li Ang, Chen Yujie, Xiao Chao. Fault Ride-Through Control Method for VSC-HVDC Balancing between DC Voltage Security and Reactive Power Support. Transactions of China Electrotechnical Society, 2024, 39(19): 6129-6144.
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2024, Vol. 39 
