基于V-I特性的多端柔性直流输电系统的控制策略

Control of multi-terminal VSC-HVDC system based on V-I characteristics

针对典型的分布式电站如大型海上风电场的柔性直流输电接入和控制问题,本文建立了一个具有两个发送端和两个接收端的多端柔性直流输电系统,说明了针对该多端直流输电系统的框架结构与运行原理,给出了一种各个换流站之间的协调控制策略。该控制策略对送端换流站采用定交流电压与定频率控制,对受端换流站,通过分析其直流网络特性,并基于受端换流站的电压-电流(V-I)特性曲线,得到了各受端换流站吸收的功率之比与其V-I特性曲线的斜率之间的关系。在此基础上提出了一种在电压外环采用比例控制的方法,推导得出了比例系数与受端换流站的V-I特性曲线的斜率之间的关系,给出了调节功率分配的方法。通过PSCAD/EMTDC仿真验证了该控制方法的正确性,仿真表明该控制方法具有良好的稳态特性和动态性能。

This paper presents control strategies of multiterminal HVDC transmission system （MTDC） using volt age source converters （VSCs） for integrating large distributed power system, such as large offshore wind farms. Theframework and operation principles of the proposed system are described and control strategies for coordinating vari ous VSCs are proposed. DC voltage control based on the DC voltagecurrent （VI） droop characteristics of grid side converters is implemented to ensure stable system operation and flexible power dispatch between various onshore AC grids. To validate the performance of the proposed control strategies, a typical four terminal MTDC network, which connecting two offshore wind farms with two onshore AC grids, is established in PSCAD/EMTEC. Simulation re sults under normal and abnormal operation conditions verify the satisfactory performance of the proposed control strategy and correctness of the theoretical analysis.