柔性直流互联电网的孤岛频率快速控制技术

区域小电网同时通过交流及柔性直流输电通道与其他大电网连接的互联电网,当交流输电通道故障导致区域小电网孤岛时,柔性直流系统的定有功功率控制方式限制了大电网对孤岛的支援能力。根据柔性直流系统具有潮流控制快速可靠的特点,设计了一种基于离线计算与在线判断相结合的柔性直流互联电网的孤岛频率快速控制方案。首先,通过离线策略初步确定功率缺额,随后根据在线频率变化率判定采取粗调或精调的实际控制措施,用于粗调的离线计算结果使得在线判断时计算量小、采样少,动作快速;用于精调的频率限制控制器(frequency limit controller,FLC)可以实现无差调节,能够对粗调结果进行补充,增强可靠性,并能与区域电网的切机(负荷)措施紧密配合。仿真结果表明,所提的故障孤岛频率快速控制方案能够有效解决孤岛系统频率稳定问题。

Fast Control Technology of Isolated Frequency for VSC-HVDC Interconnected Grid

The regional power grid is connected with other large power grid through the AC and VSC-HVDC transmission channels.When AC transmission channel fault leads to the regional power grid isolated,active power control mode of VSC-HVDC limits the ability of large power grid to support regional power grid.According to the fast and reliable characteristics of VSC-HVDC power flow control,this paper designs an isolated frequency fast control scheme of VSC-HVDC interconnected grid based on the combination of offline calculation and online judgment.First of all,through the offline strategy we preliminarily determine the power shortage,and then select coarse or fine tuning actual control measures according to the on-line frequency change rate.The off-line calculation results for coarse tuning make online judge have small computation,less sampling,fast action;the frequency limit controller (FLC) for fine tuning can achieve non differential regulation,supplement the coarse tuning results,improve the reliability and work closely with the regional power grid cut off generator (load).The simulation results show that the proposed frequency fast control scheme of fault island can effectively solve the problem of frequency stability.