受端混联型多端直流输电系统逆变侧交流故障特性分析及协调控制策略

受端混联型多端直流输电系统具有很好的工程应用前景，但受端不同换流站在交流故障时的耦合特性复杂，其控制策略应能适应各站交流故障穿越的需求。首先研究了受端混联系统逆变侧并联模块化多电平换流器(modular multilevel converter, MMC)侧交流故障时的电流不平衡、过压过流机理，以及电网换相换流器(line commutated converter, LCC)侧交流故障时的功率返送机理。然后，基于故障特性提出了一种简单的协调控制策略，即通过在MMC从站配置基于有功不平衡量的电压补偿来实现并联站间电流平衡，通过设计合适的LCC定电流整定控制来解决严重过压问题。最后基于白鹤滩—江苏多端直流输电工程实际参数的电磁暂态仿真结果，验证了对故障机理分析的正确性和所提控制策略的有效性。协调控制策略不仅能有效解决MMC功率和电流不平衡问题、减小过压过流和避免功率返送，还能改善系统恢复性能，提升系统安全稳定性。

AC fault characteristics analysis and coordinated control strategy on the inverter side of a receiving-end hybrid multi-terminal HVDC system

The receiving-end hybrid multi-terminal HVDC transmission system has good engineering application prospects, but the coupling characteristics of the receiving-end when AC faults occur in different converter stations are complex, and the control strategy should be able to adapt to the AC fault ride-through requirements of each station. First, this paper studies the fault mechanisms of current imbalance, over-voltage and over-current when an AC fault occurs in the parallel modular multilevel converter (MMC) side of the inverter side of the receiver-side hybrid DC system, and the power return mechanism when an AC fault occurs in the LCC side of the receiver side. Then, based on the fault characteristics, a simple coordinated control strategy is proposed. That is, the current balance between parallel stations is realized by configuring voltage compensation based on active power imbalance in MMC slave stations; the serious overvoltage problem is solved by designing appropriate LCC constant current setting control. Finally, an electromagnetic transient simulation based on the actual parameters of the Baihetan-Jiangsu multi terminal HVDC transmission project verifies the correctness of the fault mechanism analysis and the effectiveness of the proposed control strategy. The coordinated control strategy can not only effectively solve the power and current imbalance problem of the MMC, reduce over-voltage and over-current and avoid power return, but also improve the recovery and security and stability of the system.