基于交叉熵的海上风电经柔性低频送出系统海缆纵联保护

Pilot Protection Scheme of Submarine Cable in Flexible Low-Frequency Transmission System Based on Cross Entropy Algorithm

柔性低频输电系统交流海缆线路两侧为电力电子换流器,故障电流特性由换流器控制策略决定,与传统同步电源存在差别,导致传统电流差动保护存在不正确动作风险。为解决此问题,基于海上风电经柔性低频输电送出系统海缆线路的故障电流特性,对传统电流差动保护进行了动作性能分析,揭示了动作性能下降的原因,提出了一种基于交叉熵算法的新型纵联保护方案。该方案先对一侧电流采样值进行虚拟负电容补偿和相反数处理,再计算其与另一侧电流的交叉熵,根据交叉熵的变化判断区外和区内故障。硬件在环实验结果表明:该方案能在海缆发生各种类型故障时正确动作,抗高过渡电阻的能力强,同时对TA测量误差具备良好的耐受能力,可作为柔性低频输电海缆的主保护。

There are power electronic converters on both sides of the AC submarine line of flexible low-frequency transmission system,and the fault current characteristics are determined by the converter control strategy,which is different from the traditional synchronous power supply,which will lead to the risk of incorrect operation of the traditional current differential protection.Based on the fault current characteristics of offshore wind power transmission system cable line,this paper analyzes the operational performance of traditional current differential protection and reveals the reasons for the decline of operational performance.In this paper,a novel pilot protection scheme based on cross entropy algorithm is proposed.In this scheme,virtual negative capacitance compensation and negative number processing are carried out on the sampled current of one side,and then the cross entropy between the sampled current and the current of the other side is calculated.According to the change of cross entropy,external and internal faults are judged.The hardware in-loop test results show that the scheme can operate correctly when various types of faults occur in the submarine cable,and has strong resistance to high transition resistance.It can also operate correctly when there are measurement errors in TA.It can be used as a primary protection for flexible low-frequency transmission submarine.