MMC-HVDC互联系统协调控制策略与频率响应分析

Coordinated Control Strategy and Frequency Response Analysis for Interconnected MMC-MTDC Transmission System

摘要:

模块化多电平换流器(modular multilevel converter,MMC)型直流输电技术是近年来新能源集中送出和远距离异步联网较好的解决方案。负荷变化通过直流电网对交流系统产生的频率响应是一个重点研究课题。研究了基于模块化多电平换流器的多端柔性直流输电(modular multilevel converter based multi-terminal high voltage direct current,MMC-MTDC)系统的协调控制策略,通过交流电网的频率下垂控制和MMC换流站的直流电压下垂控制实现瞬时功率的平衡。通过引入换流站附加频率控制策略,使某个换流站交流系统出现负荷-频率变化时其他交流系统可以通过直流电网参与功率和频率调整,并进行理论推导频率响应关系,得出频率响应矩阵。在PSCADX4/EMTDC仿真软件搭建四端直流电网模型进行验证,结果表明控制策略的有效性与频率响应分析的可行性。

关键词:MMC-MTDC;互联系统;协调控制;电压下垂控制;频率响应;

Abstract:

Modular multilevel converter based HVDC technology is a good solution to the centralized dispatch of new energy sources and remote asynchronous interconnection in recent years． The response of load /frequency variation to the AC system through the DC power grid is a key research topic． The coordinated control strategy of multi － terminal flexible DC transmission system based on modular multilevel converter ( MMC － MTDC) is studied，which realizes the balance of instantaneous power by means of frequency droop control of AC power grid and DC voltage droop control of MMC converter station． By introducing the additional frequency control strategy of converter station，the AC system can be used to participate in the power and frequency response through the DC power grid when the load frequency changes in the AC system of a converter station，and the frequency response matrix is obtained by theoretical derivation． The simulation results show that the effectiveness of control strategy and the feasibility of frequency response analysis are verified by the four terminal DC power grid model with PSCADX4 /EMTDC simulation software．

Key words:MMC － MTDC; interconnected system; coordinated control; voltage droop control; frequency response