一种基于模块化多电平换流器的多端高压直流输电系统协调控制方法

针对基于模块化多电平换流器的多端高压直流输电系统(modular multilevel converter based multi-terminal DC,MMC-MTDC)中,交流区域的负荷波动导致该区域功率短暂不平衡,造成区域内电网频率波动的问题,首先提出一种基于虚拟同步发电机(virtual synchronous generator, VSG)的换流器控制方法。其次,针对在应用VSG策略调频过程中会改变换流站的输出功率,打破直流侧的功率平衡,而导致直流电压偏差过大,当存在线路阻抗时影响尤为明显的问题,将VSG控制与改进下垂控制相结合,形成MMCMTDC系统多站综合协调控制策略。该控制方法不仅可以为交流区域提供频率支持,还能优化直流母线上不平衡功率的分配,提高系统直流电压的稳定性。最后,基于Matlab/Simulink构建5端MMC-MTDC系统进行仿真,仿真结果验证了所提控制策略的有效性。     

柔性直流输电系统中虚拟同步发电机技术研究综述

虚拟同步发电机技术(VSG)通过对同步发电机(SG)的惯性响应和有功-频率下垂特性的模拟,可为交流网络提供频率支撑。介绍了基于电压源换流器的柔性直流输电(VSC-HVDC)系统的发展以及换流器控制方式,对能为本地交流网络以及互联的异步交流网络提供频率支撑的VSG技术进行了解释;基于现有学术研究,对VSC-HVDC系统中VSG控制技术的应用进行综述;阐述了VSG控制中引入直流电压控制以及采用多VSG并联控制有可能会出现的问题,指出如何克服或减小该问题的影响是未来研究的方向。     

Integrated reliability of travel time and capacity of urban road network under ice and snowfall conditions

In order to evaluate and integrate travel time reliability and capacity reliability of a road network subjected to ice and snowfall conditions,the conceptions of travel time reliability and capacity reliability were defined under special conditions.The link travel time model(ice and snowfall based-bureau public road,ISB-BPR) and the path choice decision model(elastic demand user equilibrium,EDUE) were proposed.The integrated reliability was defined and the model was set up.Monte Carlo simulation was used to...