柔性直流电网潮流转移特性及安全运行影响分析

直流电网潮流大范围转移可能导致换流站运行于安全边界之外,进而引发直流系统连锁故障。为厘清不同情况下直流系统潮流分布转移特性及其对安全运行的影响,首先在主从控制、下垂控制方式下分别对故障线路切除和换流站注入功率改变后潮流转移特性进行了理论分析,并得出了不同运行方式下潮流转移定量计算方法。然后基于PQ功率域分析了复杂直流电网中各站的安全运行边界,明确了不同运行方式及不同控制模式受潮流转移及安全边界双重影响的规律。最后,通过CIGRE柔直电网测试模型对所提计算方法及安全边界分析结论进行了仿真。基于PSCAD软件的仿真结果验证了理论分析的正确性。

Analysis of power flow transfer characteristics and influence on the safety operation of a flexible DC grid

The large-scale transfer of DC power flow may cause a converter station to operate outside safety limits. This may cause cascading failures in the DC system. In order to clarify the power flow distribution and transfer characteristics of a DC system under different conditions and its impact on safe operation, first, this paper analyzes the characteristics of power flow transfer after removing the faulty line or changing the injected power of a converter station under master-slave control and droop control. It obtains a quantitative calculation method for power flow transfer in different operational modes. Then, based on PQ power domain, the safe operation boundary of each station in a complex DC grid is analyzed. The rules of different operational and control modes affected by power flow transfer and safety boundary are clarified. Finally, this paper simulates the proposed calculation method and the conclusion of security boundary analysis through the CIGRE DC grid test model. The simulation results based on PSCAD software confirm the correctness of the theoretical analysis. This work is supported by the National Key Research and Development Program of China (No. 2018YFB0904600).