适用于海上风电接入的多端柔直网内不平衡功率优化分配控制策略

Control Strategy on Optimal Redistribution of Unbalanced Power for Offshore Wind Farms Integrated VSC-MTDC

针对海上风电场接入的基于电压源变流器的多端柔性直流输电系统中风能波动频繁引起的功率不平衡问题,提出一种考虑不平衡功率经济分配的自适应、分层改进电压下垂控制策略。详细推导了换流阀侧物理量所表示的不平衡功率产生后附加发电费用的等效表达式。基于公共直流参考电压和等效附加耗量成本的微增率曲线,所设计的控制策略能够在不依赖通信和中央控制的情况下,自适应实现不平衡功率的经济分配。结合控制特性分析和稳定性分析研究了控制器参数的选取原则。最后,在PSCAD/EMTDC仿真平台中搭建了辐射状4端柔直模型,验证了改进控制策略的有效性。仿真结果表明,该策略在正常工况下的附加发电成本显著降低,在故障工况下仍可维持直流电压稳定和有功功率平衡。

In this paper,for a voltage source converter based multi-terminal DC transmission(VSC-MTDC)system connected with offshore wind farms,a self-adaptive and hierarchical control scheme was proposed to consider the optimal allocation of imbalanced power when wind energy fluctuation occurred frequently.The equivalent extra cost function in the form of active/reactive power and voltage on the valve side was deduced firstly in details.Based on the incremental cost curve of extra generation and DC voltage at the point of common coupling(PCC),the scheme can locally make the unbalanced power be shared economically without central controller,having similar effect to the equal increment principle(EIP).Principles of control parameters setting was discussed based on control characteristic analysis and stability analysis.Finally,a 4-terminal radial system was used to verify the effectiveness in PSCAD/EMTDC simulation platform.The results show that the proposed scheme can reduce the extra generation cost effectively under normal conditions,and maintain DC voltage stability and power balance when the fault occurs.