考虑功率裕度的VSC-MTDC系统改进下垂控制策略

A Novel Droop Control Strategy Taking into Account the Available Headroom for VSC-MTDC System

针对VSC-MTDC系统下垂控制策略未考虑到换流站实际运行工况这一不足之处,提出一种考虑功率裕度的改进下垂控制策略。改进策略中主导站下垂系数的选取与换流站容量无关,而是由功率裕度决定,可以避免主导站出现不必要的满载现象;同时,在定有功功率站中引入偏差下垂控制,避免直流网络的功率不平衡过大导致直流电压失稳的情况。PSCAD/EMTDC环境下的仿真结果表明,该方法保证了初始功率裕度较小的换流站分担较少的不平衡功率,初始功率裕度较大的换流站承担较多的不平衡功率,实现了不平衡功率的合理分配。

The DC voltage droop control strategy of VSC-MTDC system can ensure proper distribution according to the converter ratings.However,it does not consider the actual loading condition. In order to solve this defect,a novel scheme for appropriate power sharing taking into account the available headroom of each converter station was proposed,and possible overloading was avoided. The margin droop control strategy was introduced in the active-power controller to ensure the stability of DC voltage. Transient simulations in PSCAD / EMTDC showed that the converters which are already operating close to the limits would try to share less burden of the loss to the extent of the other converters with higher spare capacity or headroom and thus the unbalanced power would be appropriate assigned.