交直流混合电力系统的安全校正策略

The Security Correction Strategy in AC and DC Hybrid Power System

随着交直流混合电力系统的迅速发展,直流闭锁或线路故障引发系统连锁故障的风险增加,故需要根据电网运行状态采取相应的控制措施避免潮流进一步过载。在智能电网背景下,考虑将直流和可控串联补偿器(TCSC)也作为控制措施以进一步减少负荷切除量。制定安全校正策略常用的方法有灵敏度法和优化规划法。灵敏度法便于在线切机切负荷控制,分析了直流功率和TCSC电抗值的支路潮流灵敏度是控制量的函数并非定值,故在交直流混合电力系统的安全校正策略制定中应用灵敏度法有一定困难。针对优化规划法优化变量多、计算时间长、难以在线实施,提出采用启发式搜索原理缩减优化变量数量的优化规划法,该方法基于负荷转移因子(LSF)筛选出对待调节支路控制效果最好的发电机和负荷节点,将这些节点的功率与直流功率以及TCSC电抗值一同作为优化变量,以负荷总切除量最小即经济性最佳为目标函数建立优化模型并采用智能优化算法求解,能够在较短时间内得到安全校正方案。基于改造的IEEE30节点算例系统,通过与不采用启发式搜索以及不考虑将直流功率和TCSC电抗值作为优化变量得到的结果相比较,该方法的有效性及优越性得到验证。

With the rapid development of AC-DC hybrid power system, the risk of cascading failures caused by DC block or line tripping is also increasing. Relevant control measures should be taken to avoid further overload according to the operation status of power grid. In smart grid, HVDC and thyristor controlled series capacitor（ TCSC） can also be taken as control measures to further reduce the amount of load shedding. The sensitivity and optimization based methods are often utilized to formulate the security correction strategies. The sensitivity based method functions well in online generation rescheduling and load shedding. However,the power flow sensitivities of DC power and TCSC reactance are discovered to vary according to control variable rather than being constant. So it＇s difficult for the sensitivity based method to be applied to security correction strategy of AC / DC hybrid power system. A modified optimization method, which uses heuristic search principle, is proposed against the defects of excessive optimization variables and heavy computational burden,which results in the limitation for online application. Based on load shift factor（ LSF）,few generator and load nodes are rapidly selected to control overload effectively. Aiming at the minimum amount of load shedding,an optimization model is proposed,in which HVDC power and reactance of TCSC, in addition to the power of the selected nodes are taken as optimization variables. Intelligent optimization algorithm is adopted to obtain security correction scheme. Based on modified IEEE 30-node benchmark, the validity and superiority of the proposed method is verified by comparing the result obtained by the proposed method with those without utility of heuristic search or without taking DC power and TCSC reactance into consideration.