VSC-MTDC系统下垂控制优化策略

直流电压稳定和系统功率平衡是直流输电系统稳定运行的关键条件。下垂控制不依赖于站间高速通信,为远距离输电提供了有效的技术支持,但其存在直流电压控制刚性较差,下垂系数设置不当易造成系统控制不稳定和换流站过载运行等一系列问题。为解决这类问题,先求解出三端柔性直流输电直流网络的V-I特性关系,分析下垂系数的作用原理,随后求取V-I特性曲线边界条件,最后提出一种下垂控制优化策略,对下垂系数设置影响因子,使系统根据需要动态改变下垂系数,从而运行在适宜的工况。使用PSCAD/EMTDC平台搭建了三端柔性直流输电仿真系统,经过稳态分析和暂态分析证明了所提出优化策略的正确性和有效性。

Optimized Droop Control Strategy for Voltage Sourced Converter Based Multi-terminal HVDC

The balance between DC voltage stability and system power is a prerequisite for the stable operation of HVDC system.Since drop control does not depend on the high-speed communication between stations,it provides effec?tive technical support for long-distance power transmission.However,its DC voltage control rigidity is relatively poorer,and the improper setting of droop coefficient will easily leads to problems such as the instability of system control and the overload operation of the converter station.To solve this kind of e problems,the relation between voltage and current of a three-terminal flexible HVDC network is solved at first.Then,the action principle of droop coefficient is analyzed,and the boundary condition of the V-I characteristic curve is obtained.Finally,an optimized droop control strategy is pro?posed,in which an influencing factor is set on the droop coefficient,so that the system can dynamically change the droop coefficient according to needs.In this way,the system can always run in suitable working conditions.A three-terminal flexible HVDC transmission simulation system is built on the PSCAD/EMTDC platform,and the correctness and effec?tiveness of the proposed optimized strategy are verified by steady-state and transient analyses.