风电经架空线双极MMC-HVDC并网的直流故障穿越协调控制策略

Coordinated Control Strategies for DC Fault Ride-through of Wind Power Integration via Bipolar MMC-HVDC Overhead Lines

采用架空线柔性直流输电技术进行远距离输电是大规模风电场友好型并网的有效手段。针对架空线路易发生故障的问题,采用对称双极主接线并配置直流断路器是其主要解决方案之一。该文基于双极接线方案运行方式灵活及直流断路器的故障清除能力,提出风电经架空线基于模块化多电平换流器的柔性直流输电(modular multilevel converter based high voltage direct current,MMC-HVDC)并网的直流故障穿越协调控制策略。根据非故障极的功率转带能力,将故障清除后的不平衡功率分配划分为自消纳情景和非自消纳情景。针对自消纳情景,通过合理切换双极MMC的控制模式,可在提高非故障极功率转带能力的同时自主消纳不平衡功率,进而有效降低转移功率的影响范围;针对非自消纳情景,设计考虑风机转速约束的风电场超速减载协调控制策略,优化分配各风电机组承担的减载功率,充分利用其转子动能和捕获风功率的变化实现精确减载;同时通过控制模式切换使非故障极MMC自主运行于满载状态,减小单极退出运行对受端交流系统的影响。最后,基于Matlab/Simulink仿真模型验证所提直流故障穿越协调控制策略的有效性。

Modular multilevel converter based high voltage direct current(MMC-HVDC)technology using long-distance overhead lines is an effective means for large-scale wind farm integration.Aiming at the problem that overhead lines are vulnerable to faults,one of the main solutions is to use symmetrical bipolar main wiring and configure DC circuit breakers.Based on the flexible operation mode of bipolar wiring scheme and the fault clearance capability of DC circuit breakers,coordinated control strategies for DC fault ride-through of wind power integration via MMC-HVDC overhead lines were proposed.According to the power transfer capability of non-fault poles,the unbalanced power redistribution after fault clearance can be divided into self-absorption scenario and non-self-absorption scenario.For self-absorption scenario,by switching control mode of bipolar MMC reasonably to improve the power transfer capability of non-fault poles,which can actively absorb unbalanced power,and reduce the influence range of transfer power effectively.For non-self-absorption scenario,a coordinated control strategy for over-speed load-shedding of wind farms considering speed constraints was designed to achieve the optimal distribution of load-shedding power among wind turbines,so the accurate load shedding can be achieved by making full use of rotor kinetic energy and the change of captured wind power.At the same time,the non-fault pole MMC actively operates at full load state by switching control mode to reduce the impact of unipolar withdrawal on the receiving end system.Finally,effectiveness of the coordinated control strategies for DC fault ride-through is verified by Matlab/Simulink simulation.