Distinction of weak and strong AC grids for emerging hierarchical-infeed LCC-UHVDC systems is important for planning and operation departments. However, accuracy of earlier distinction methods is limited as they were ...Distinction of weak and strong AC grids for emerging hierarchical-infeed LCC-UHVDC systems is important for planning and operation departments. However, accuracy of earlier distinction methods is limited as they were developed by empirical reasoning without rigorous theoretical analysis. Hence in this letter, hierarchical-infeed interactive effective short-circuit ratio (HIESCR) index is first used for strength evaluation of HIDC systems with complex inter-inverter interactions considered. Boundary HIESCR (BHIESCR) is also introduced in the proposed distinction method of weak and strong AC grids. That is, weak (or strong) AC grids are, respectively, identified when HIESCR is less (or greater) than BHIESCR. Second, it is shown BHIESCR remains almost unchanged as 3.0 versus various system parameters and rated operation variables based on rigorous theoretical analysis. This salient feature makes the proposed method more accurate than earlier methods. Finally, the proposed method is validated by simulations based on the PSCAD/EMTDC program.展开更多
This paper deals with the operation and performance of VSC （voltage source converter） based HVDC （high voltage direct current） interconnecting two extremely weak AC networks, the experience of Caprivilink project....This paper deals with the operation and performance of VSC （voltage source converter） based HVDC （high voltage direct current） interconnecting two extremely weak AC networks, the experience of Caprivilink project. It is shown in the paper that the HVDC converter automatically provides the supreme voltage and frequency stabilizing function when a critical situation is detected, no matter the disturbances appeared in sending end or receiving end AC networks. This supreme voltage and frequency stabilizing function makes it possible to avoid the blackout even if all the generators are tripped under an extra-ordinary worst contingency. By plots of recorded transients, the paper will show how the eventual blackouts are avoided.展开更多
新能源汇集经柔性直流输电(voltage source converter based high voltage direct current,VSC-HVDC)技术送出是促进新能源消纳的有效方式。但新能源渗透率的持续增加导致电网强度不断下降,采用传统跟网型(grid-following,GFL)换流技术...新能源汇集经柔性直流输电(voltage source converter based high voltage direct current,VSC-HVDC)技术送出是促进新能源消纳的有效方式。但新能源渗透率的持续增加导致电网强度不断下降,采用传统跟网型(grid-following,GFL)换流技术已无法满足系统稳定运行需求。为提高系统弱电网适应性,满足大规模新能源接入弱同步支撑柔直系统应用场景需求,提出在柔直系统送端换流站采用VSG控制策略。首先,建立整流侧控制小信号数学模型,利用根轨迹法深入研究虚拟阻抗对系统稳定性的影响。其次,提出利用交流电压变化率及电压差值等电气量构建虚拟电抗自适应调整项的改进VSG控制算法,在保证系统等效阻抗呈感性的同时,可提高送端交流系统的等效短路比,达到改善系统整体性能的效果。最后,通过PSCAD/EMTDC电磁暂态仿真验证所提控制策略的有效性。展开更多
In recent years,the penetration of renewable resources into AC power systems has increased tremendously,creating a significantly impact on the latter’s operations and stability.In this respect,it is also important to...In recent years,the penetration of renewable resources into AC power systems has increased tremendously,creating a significantly impact on the latter’s operations and stability.In this respect,it is also important to gain a basic analytical understanding of such impact on the steady-state stability of power systems with electrically weak AC/DC interconnections,but such works are not very evident in the literature.Therefore,a classical analytic model of the single and multi-infeed HVDC system which now incorporates renewable resources is proposed.Then the well-established concept of voltage sensitivity of the AC/DC interconnection is applied to analyze the impact of the renewable resources on the steady-state stability of these composite system models,as well as on the influence of system conditions and parameters.This impact is also compared with that arising from other types of shunt devices alternatively connected at the same AC/DC interconnection,therefore their relative beneficial or negative impacts will also be benchmarked.展开更多
Based on subsynchronous oscillation(SsO)caused by the connection of a direct drive wind farm to a weak alternating current(AC)grid,a complex torque model is proposed.By dividing the wind farm into a direct current cap...Based on subsynchronous oscillation(SsO)caused by the connection of a direct drive wind farm to a weak alternating current(AC)grid,a complex torque model is proposed.By dividing the wind farm into a direct current capacitor and electrical control part,the analytical expression of damping torque for the electrical control part is deduced and the mechanism of system subsynchronous oscillation is analyzed from the perspective of damping.The system stability is determined based on a damping coefficient less than O,and the influence laws of grid strength,operating conditions,and control parameters on system damping characteristics are analyzed,based on additional subsynchronous oscillation damping control(SSDC)to suppress SsO.Furthermore,the complex torque model of the parallel access system for multiple sub-wind farms is established,and the dynamic interaction between multiple sub-wind farms is preliminarily explored.The time-domain simulation model is built in EMTDC/PSCAD to verify the correctness of the theoretical analysis.展开更多
小水电群富集的地区电网与主网的交流联络较弱时,容易引起系统低频振荡问题。用电压源换流器型直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)异步联接小水电群电网与主网的方式可...小水电群富集的地区电网与主网的交流联络较弱时,容易引起系统低频振荡问题。用电压源换流器型直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)异步联接小水电群电网与主网的方式可消除小水电群引起的低频振荡问题。但小水电群电网属于弱交流系统,此场景下VSC-HVDC有必要参与弱交流系统的电压和频率控制。该文设计了一种改善交流系统暂态稳定性的VSC-HVDC交流电压–频率协调控制策略,该策略的首要控制目标是保证VSC-HVDC设备的安全,第二控制目标是提高交流系统的电压稳定性,第三控制目标是提高交流系统的频率稳定性。设计的协调控制器结构能够确保暂态过程中多个控制目标按照优先级顺序实现。以云南电网的实例分析表明:VSC-HVDC异步联网方案能够有效提高系统的小扰动稳定性水平;VSC-HVDC交流电压–频率协调控制策略能够改善交流系统的暂态稳定性。展开更多
当逆变侧交流系统发生故障引发换相失败时会导致送端母线出现过电压,特别是针对于弱送端交流电网,其过电压情形更加严重。提出了一种基于晶闸管全桥耗能子模块(thyristor full bridge power-consumption sub module,PCT-FBSM)的直流斩波...当逆变侧交流系统发生故障引发换相失败时会导致送端母线出现过电压,特别是针对于弱送端交流电网,其过电压情形更加严重。提出了一种基于晶闸管全桥耗能子模块(thyristor full bridge power-consumption sub module,PCT-FBSM)的直流斩波器(DC Chopper)拓扑结构,可以有效地抑制由换相失败引发的送端暂态过电压。文中首先分析了DC Chopper抑制过电压的机理,介绍了DC Chopper子模块的6种工作模式,然后设计了子模块在不同工况下的控制策略,并提出了子模块参数的设计方法,最后在PSCAD/EMTDC环境中搭建了相应的仿真模型,对所提拓扑结构对暂态过电压的抑制效果以及系统的运行特性进行了仿真分析,仿真结果表明所提DC Chopper可以有效抑制弱送端电网的暂态过电压。展开更多
基金supported in part by the National Natural Science Foundation of China(51907067)in part by the Industrial Research Chair Program of the Natural Sciences and Engineering Research Councilof Canada。
文摘Distinction of weak and strong AC grids for emerging hierarchical-infeed LCC-UHVDC systems is important for planning and operation departments. However, accuracy of earlier distinction methods is limited as they were developed by empirical reasoning without rigorous theoretical analysis. Hence in this letter, hierarchical-infeed interactive effective short-circuit ratio (HIESCR) index is first used for strength evaluation of HIDC systems with complex inter-inverter interactions considered. Boundary HIESCR (BHIESCR) is also introduced in the proposed distinction method of weak and strong AC grids. That is, weak (or strong) AC grids are, respectively, identified when HIESCR is less (or greater) than BHIESCR. Second, it is shown BHIESCR remains almost unchanged as 3.0 versus various system parameters and rated operation variables based on rigorous theoretical analysis. This salient feature makes the proposed method more accurate than earlier methods. Finally, the proposed method is validated by simulations based on the PSCAD/EMTDC program.
文摘This paper deals with the operation and performance of VSC （voltage source converter） based HVDC （high voltage direct current） interconnecting two extremely weak AC networks, the experience of Caprivilink project. It is shown in the paper that the HVDC converter automatically provides the supreme voltage and frequency stabilizing function when a critical situation is detected, no matter the disturbances appeared in sending end or receiving end AC networks. This supreme voltage and frequency stabilizing function makes it possible to avoid the blackout even if all the generators are tripped under an extra-ordinary worst contingency. By plots of recorded transients, the paper will show how the eventual blackouts are avoided.
文摘新能源汇集经柔性直流输电(voltage source converter based high voltage direct current,VSC-HVDC)技术送出是促进新能源消纳的有效方式。但新能源渗透率的持续增加导致电网强度不断下降,采用传统跟网型(grid-following,GFL)换流技术已无法满足系统稳定运行需求。为提高系统弱电网适应性,满足大规模新能源接入弱同步支撑柔直系统应用场景需求,提出在柔直系统送端换流站采用VSG控制策略。首先,建立整流侧控制小信号数学模型,利用根轨迹法深入研究虚拟阻抗对系统稳定性的影响。其次,提出利用交流电压变化率及电压差值等电气量构建虚拟电抗自适应调整项的改进VSG控制算法,在保证系统等效阻抗呈感性的同时,可提高送端交流系统的等效短路比,达到改善系统整体性能的效果。最后,通过PSCAD/EMTDC电磁暂态仿真验证所提控制策略的有效性。
文摘In recent years,the penetration of renewable resources into AC power systems has increased tremendously,creating a significantly impact on the latter’s operations and stability.In this respect,it is also important to gain a basic analytical understanding of such impact on the steady-state stability of power systems with electrically weak AC/DC interconnections,but such works are not very evident in the literature.Therefore,a classical analytic model of the single and multi-infeed HVDC system which now incorporates renewable resources is proposed.Then the well-established concept of voltage sensitivity of the AC/DC interconnection is applied to analyze the impact of the renewable resources on the steady-state stability of these composite system models,as well as on the influence of system conditions and parameters.This impact is also compared with that arising from other types of shunt devices alternatively connected at the same AC/DC interconnection,therefore their relative beneficial or negative impacts will also be benchmarked.
基金supported by Integrated project of National Natural Science Foundation of China(No.U1866601)Science and Technology Project of State Grid Corporation of China(5230DK20004V)。
文摘Based on subsynchronous oscillation(SsO)caused by the connection of a direct drive wind farm to a weak alternating current(AC)grid,a complex torque model is proposed.By dividing the wind farm into a direct current capacitor and electrical control part,the analytical expression of damping torque for the electrical control part is deduced and the mechanism of system subsynchronous oscillation is analyzed from the perspective of damping.The system stability is determined based on a damping coefficient less than O,and the influence laws of grid strength,operating conditions,and control parameters on system damping characteristics are analyzed,based on additional subsynchronous oscillation damping control(SSDC)to suppress SsO.Furthermore,the complex torque model of the parallel access system for multiple sub-wind farms is established,and the dynamic interaction between multiple sub-wind farms is preliminarily explored.The time-domain simulation model is built in EMTDC/PSCAD to verify the correctness of the theoretical analysis.
文摘小水电群富集的地区电网与主网的交流联络较弱时,容易引起系统低频振荡问题。用电压源换流器型直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)异步联接小水电群电网与主网的方式可消除小水电群引起的低频振荡问题。但小水电群电网属于弱交流系统,此场景下VSC-HVDC有必要参与弱交流系统的电压和频率控制。该文设计了一种改善交流系统暂态稳定性的VSC-HVDC交流电压–频率协调控制策略,该策略的首要控制目标是保证VSC-HVDC设备的安全,第二控制目标是提高交流系统的电压稳定性,第三控制目标是提高交流系统的频率稳定性。设计的协调控制器结构能够确保暂态过程中多个控制目标按照优先级顺序实现。以云南电网的实例分析表明:VSC-HVDC异步联网方案能够有效提高系统的小扰动稳定性水平;VSC-HVDC交流电压–频率协调控制策略能够改善交流系统的暂态稳定性。
文摘当逆变侧交流系统发生故障引发换相失败时会导致送端母线出现过电压,特别是针对于弱送端交流电网,其过电压情形更加严重。提出了一种基于晶闸管全桥耗能子模块(thyristor full bridge power-consumption sub module,PCT-FBSM)的直流斩波器(DC Chopper)拓扑结构,可以有效地抑制由换相失败引发的送端暂态过电压。文中首先分析了DC Chopper抑制过电压的机理,介绍了DC Chopper子模块的6种工作模式,然后设计了子模块在不同工况下的控制策略,并提出了子模块参数的设计方法,最后在PSCAD/EMTDC环境中搭建了相应的仿真模型,对所提拓扑结构对暂态过电压的抑制效果以及系统的运行特性进行了仿真分析,仿真结果表明所提DC Chopper可以有效抑制弱送端电网的暂态过电压。
