The close proximity and the necessity of coordination between multiple high-voltage direct currents(HVDCs)raise the issue of grid partitioning in multi-infeed HVDC systems.A multi-objective partition strategy is propo...The close proximity and the necessity of coordination between multiple high-voltage direct currents(HVDCs)raise the issue of grid partitioning in multi-infeed HVDC systems.A multi-objective partition strategy is proposed in this paper.Several types of relationships to be coordinated and complemented are analyzed and formulated using quantitative indices.According to the graph theory,the HVDC partition is transformed into a graph-cut problem and solved via the spectral clustering algorithm.Finally,the proposed method is validated for a practical multi-HVDC grid,confirming its feasibility and effectiveness.展开更多
In multi-infeed HVDC system, the interactions and influences between DC systems AC systems are complex as the electrical distances among DC converter stations which are relatively short. Multi-infeed interaction facto...In multi-infeed HVDC system, the interactions and influences between DC systems AC systems are complex as the electrical distances among DC converter stations which are relatively short. Multi-infeed interaction factor (MIIF) can effectively reflect the interaction among DC systems. The paper theoretically analyzes the impact factors of MIIF like the electrical distances between two DC converter stations and the equivalent impedance of the receiving end AC system. By applying the Kirchhoff’s current law on the inverter AC bus, the paper deduces the analytical expressions for MIIF. From the expression, it is clear how the equivalent impedance of AC system and coupling impedance can affect MIIF. PSCAD simulations validate the effectiveness and the correctness of the proposed expression and some useful conclusions are drawn.展开更多
More and more high voltage direct current(HVDC) converters are being located in a load area in the Yangtze River Delta Region in China. It's large transmission capacity and intensive placement are hardly seen in o...More and more high voltage direct current(HVDC) converters are being located in a load area in the Yangtze River Delta Region in China. It's large transmission capacity and intensive placement are hardly seen in other countries. Accurate and reliable study tools and methods are extremely needed for power system engineers and researchers to deal with such problems which were never met before and otherwhere. A novel approach on electromagnetic modeling of alternating current / direct current(AC/DC) system is proposed and simulation is carried out to replay a real AC 3-phase to ground fault on a multi-infeed high voltage direct current(MIHVDC) system. AC system is specially simplified. Dynamic models and real parameters are adopted in main AC/DC equipments concerned and retained. Modeling and simulation are based on the power system computer aided design/electro-magnetic transient in direct current(PSCAD/EMTDC) system software package.Comparisons between simulation results and the records from the fault recorders are studied including both AC and DC quantities.展开更多
When multiple LCC-HVDC transmission lines are densely fed into a receiving AC system,voltage dips can easily propagate in the power system,resulting in multiple LCC commutation failures simultaneously.The VSC-HVDC can...When multiple LCC-HVDC transmission lines are densely fed into a receiving AC system,voltage dips can easily propagate in the power system,resulting in multiple LCC commutation failures simultaneously.The VSC-HVDC can be used to divide the receiving sys-tem into several interconnected sub-partitions and improve the voltage support capability of the receiving system.Compared with asyn-chronous interconnection,which completely separates the receiving systems with VSC-HVDC,incomplete segmentation with an AC connection is a more pertinent segmenting method for multilayer complex regional power grids.To analyze the voltage support capability of the VSC in incomplete segmentation,a micro-incremental model of the VSC was established,the operating impedance of the VSC was calculated,and the voltage support function of the VSC was quantified.The effect of the fault on the system short-circuit capacity was analyzed,and a calculation method for the multi-infeed short-circuit ratio in an incompletely segmented scenario was obtained.A VSC-segmented model of a two-infeed DC system was built on the EMTDC/PSCAD simulation platform,and the validity of the micro-increment model and accuracy of the proposed conclusions were verified.展开更多
This paper provides a comprehensive analysis of local and concurrent commutation failure(CF)of multi-infeed high-voltage direct current(HVDC)system considering multi-infeed interaction factor(MIIF).The literature indi...This paper provides a comprehensive analysis of local and concurrent commutation failure(CF)of multi-infeed high-voltage direct current(HVDC)system considering multi-infeed interaction factor(MIIF).The literature indicates that the local CF is not influenced by MIIF,whereas this paper concludes that both the local CF and concurrent CF are influenced by MIIF.The ability of remote converter to work under reduced reactive power enables its feature to support local converter via inter-connection link.The MIIF measures the strength of electrical connectivity between converters.Higher MIIF gives a clearer path to remote converter to support local converter,but at the same time,it provides an easy path to local converter to disturb remote converter under local fault.The presence of nearby converter increases the local commutation failure immunity index(CFII)while reducing concurrent CFII.Higher MIIF causes reactive power support to flow from remote converter to local converter,which reduces the chances of CF.A mathematical approximation to calculate the increase in local CFII for multi-infeed HVDC configurations is also proposed.A power flow approach is used to model the relation between MIIF and reactive power support from remote end.The local and concurrent CFIIs are found to be inverse to each other over MIIF;therefore,it is recommended that there is an optimal value of MIIF for all converters in close electric proximity to maintain CFII at a certain level.The numerical results of established model are compared with PSCAD/EMTDC simulations.The simulation results show the details of the influence of MIIF on local CF and concurrent CF of multi-infeed HVDC,which validates the analysis presented.展开更多
High-voltage direct current(HVDC)transmission is playing an increasingly important role in modern power systems,and the resulted power/voltage stability issue has raised widespread concern.This paper presents an on-li...High-voltage direct current(HVDC)transmission is playing an increasingly important role in modern power systems,and the resulted power/voltage stability issue has raised widespread concern.This paper presents an on-line power/voltage stability index(PVSI)for multi-infeed HVDC(MIDC)systems.Different from the existing indices which are developed mainly for off-line and static analysis,the proposed PVSI can be applied in real time.Effects of system changes on stability assessment such as change of system states and control strategies are considered.Thus,helpful guidance can be provided for on-line HVDC stability and controls.The PVSI is originally deduced for single-infeed HVDC systems in an‘‘AC way’’by analyzing the power and voltage stability of both pure AC systems and HVDC systems.Moreover,its on-line application in practical MIDC systems is realized by building an equivalent single-infeed model,and utilizing nowadays measurement and communication infrastructures such as wide-area measurement system(WAMS).The effectiveness of the PVSI is verified through simulations in real-time digital simulator(RTDS).展开更多
为解决基于模块化多电平换流器的柔性直流输电系统(modular multilevel converter based high voltage direct current,MMC-HVDC)在陆上交流电网故障时出现的盈余功率问题,首先计算验证了能量预警值的合理性,并设计了自适应动作能量值,...为解决基于模块化多电平换流器的柔性直流输电系统(modular multilevel converter based high voltage direct current,MMC-HVDC)在陆上交流电网故障时出现的盈余功率问题,首先计算验证了能量预警值的合理性,并设计了自适应动作能量值,解决距离和控制转换时延造成子模块过电压的问题;然后分析网侧变流器(grid-side converter,GSC)在低压穿越期间的动态输出特性,提出了基于直流电压变化率反馈的海上换流站精准降压控制用以进行风机减载;最终通过整定协同控制的逻辑与控制参数,提出了一种基于风机精准减载与子模块电容能量协同控制的低电压故障穿越策略,解决故障期间系统能量裕度利用率低与耗能装置投资大的问题。在MATLAB/Simulink中搭建系统仿真模型验证方法有效性,并与现有方法比较。仿真结果表明,所提方法可显著减少甚至避免耗能装置的投入,且具有自适应性,可在不同故障工况下尽可能利用MMC-HVDC系统的能量裕度,尤其在故障程度较轻的工况下,能在故障消除时保留部分能量裕度,有效应对电压二次跌落,提高系统低压穿越能力。展开更多
During the power modulation process of line com-mutated converter-based high-voltage direct current(LCC-HVDC),the transient power mismatch between the fast-change converter station and the slow-response reactive power...During the power modulation process of line com-mutated converter-based high-voltage direct current(LCC-HVDC),the transient power mismatch between the fast-change converter station and the slow-response reactive power compen-sators(RPCs)can cause transient voltage disturbances at the weak sending end of the AC grid.To mitigate such voltage dis-turbances,this paper proposes a coordinated feedback power control method for the hybrid multi-infeed HVDC(HMI-HVDC)system comprising an LCC-HVDC and voltage source converter-based HVDC(VSC-HVDC)systems.The mechanism of the disturbance caused by transient power mismatch is quan-titatively analyzed,and the numerical relationship between the instantaneous unbalanced power and the AC voltage is derived.Based on the numerical relationship and considering the time-varying relationship of reactive power between converter sta-tions,the unbalanced power is set as the feedback and coordi-nately distributed among the inverter stations of VSC-HVDC,and the rectifier and the inverter stations of LCC-HVDC.Simu-lation results verify that the proposed method can effectively suppress voltage disturbance without relying on remote commu-nication,thus enhancing the operation performance of the HMI-HVDC system.展开更多
高比例、强随机性的可再生能源接入电网常导致交流传输线路过载,同时电力系统升级改造中构建的嵌入式柔性直流输电(voltage source converter based high voltage direct current, VSC-HVDC)系统的可控性没有得到充分利用。为此提出了...高比例、强随机性的可再生能源接入电网常导致交流传输线路过载,同时电力系统升级改造中构建的嵌入式柔性直流输电(voltage source converter based high voltage direct current, VSC-HVDC)系统的可控性没有得到充分利用。为此提出了一种基于功率灵敏度的嵌入式VSC-HVDC紧急控制方法,以快速缓解传输线路过载问题。首先,利用系统模型建立包含嵌入式VSC-HVDC的交流-直流功率灵敏度矩阵。然后,在实时运行中根据推导的灵敏度矩阵调整VSC-HVDC的有功功率,以应对特定的交流电网过载。在调整过程中,采用优化控制方法确保直流调整的总量最小化,同时交流线路有功功率保持在可接受的范围内。最后,通过修改的IEEE39节点系统仿真验证了该方法在多种故障工况下的有效性,可快速缓解交流线路过载并保证全网运行安全。展开更多
随着电网换相型高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)技术的广泛应用,交直流混联电网的谐波交互问题愈加复杂,建立LCC-HVDC小信号模型是分析换流器交直流谐波耦合特性的重要手段。为此...随着电网换相型高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)技术的广泛应用,交直流混联电网的谐波交互问题愈加复杂,建立LCC-HVDC小信号模型是分析换流器交直流谐波耦合特性的重要手段。为此,基于谐波状态空间理论(harmonic state space, HSS)建立双端12脉动LCC-HVDC小信号模型,不仅考虑了LCC谐波传递特性,还考虑了换流变压器联结方式、控制链路延时等因素的影响。采用模块化思想分别建立各子系统谐波状态空间模型,通过接口矩阵连接为整体,使得LCC的谐波状态空间建模在易于扩展的同时,提高了精确度。最后,给出交直流谐波传递的具体表达式,并通过PSCAD仿真验证模型的准确性。所建模型不仅为后续扩展或接入更为复杂的系统奠定了基础,还可应用于双端LCC系统谐波交互稳定性评估和系统参数优化设计。展开更多
混合级联型高压直流输电(high voltage direct current,HVDC)系统综合了电网换相换流器(line commutated converter,LCC)和模块化多电平换流器(modular multilevel converters,MMC)的优势,具有良好的工程应用前景,该文对该系统后续换相...混合级联型高压直流输电(high voltage direct current,HVDC)系统综合了电网换相换流器(line commutated converter,LCC)和模块化多电平换流器(modular multilevel converters,MMC)的优势,具有良好的工程应用前景,该文对该系统后续换相失败预判及抑制开展了研究。首先,明确了换相失败恢复期间各阶段控制器交互作用以及换相电压跌落产生的后续换相失败风险。其次,在考虑MMC与LCC端口直流电压交互作用和混合级联型HVDC系统中各控制器作用的基础上,提出了一种通过对比换相电压有效值与阈值电压的后续换相失败预判方法;然后,提出了MMC提供持续无功支持和动态更改定关断角控制(constant extinction angle control,CEAC)中关断角指令值的协调控制策略,以实现后续换相失败抑制;最后,在PSCAD/EMTDC中搭建了相应的混合级联系统电磁暂态仿真模型,对预判方法的准确性和抑制策略的有效性进行了验证。展开更多
During sending-end faults in the hybrid cascaded HVDC(HC-HVDC)system,the transient voltage drop characteristics under the interaction of the AC/DC hybrid system remain unclear,and the reactive power support provided b...During sending-end faults in the hybrid cascaded HVDC(HC-HVDC)system,the transient voltage drop characteristics under the interaction of the AC/DC hybrid system remain unclear,and the reactive power support provided by the HC-HVDC to the sending-end AC system requires further investigation.To address this problem,the reactive power interaction coupling mechanism between the sending-end AC system and the HC-HVDC is revealed,and the transient voltage mathematical model considering fault severity and duration is established.Under the dynamic change of the AC system voltage,the difference between the reactive power provided only by the reactive power compensation devices and by the combined modular multilevel converters(MMC)and reactive power compensation devices is analyzed.It is concluded that using MMC to provide a proportion of reactive power enhances the reactive power support to the AC system during faults.Then,the transient voltage model considering the reactive power support of MMC is established,and the critical reactive power consumption of line commutated converter(LCC)is quantified.It is concluded that the reactive power consumption of LCC exceeding its critical value deteriorates the transient voltage.A coordinated support strategy for the sending-end AC system based on reactive power support of MMC and reactive power regulation of LCC is proposed.It can effectively address the challenge of weakened reactive power support to the AC system due to voltage drop,thereby preventing the unbalanced reactive power from deteriorating the transient voltage,and realizing active support of the tran-sient voltage.Finally,a simulation model is established on the PSCAD/EMTDC platform,and the simulation results validate the effectiveness of the proposed strategy in supporting the transient voltage,under different fault types,durations,severities,and locations.展开更多
针对柔性直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)控制参数设计过程中存在的鲁棒性差、依赖已知电路参数、工程设计经验化等问题,提出一种基于马尔科夫转换场(Markov transiti...针对柔性直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)控制参数设计过程中存在的鲁棒性差、依赖已知电路参数、工程设计经验化等问题,提出一种基于马尔科夫转换场(Markov transition field,MTF)与深度确定性策略梯度算法(deep deterministic policy gradient,DDPG)结合的鲁棒性强、不依赖电路参数特性以及可视化的VSC-HVDC控制参数优化设计方法。首先,采用马尔科夫转换场将电路功率、电压等一维时序波形数据转换为二维马尔科夫转换场域图像并使用马尔科夫转换场损失函数(Markov transition field loss,MTFL)判断二维转换域图的数据波动性;其次,将MTFL损失函数与DDPG算法相结合,综合利用MTFL损失函数对系统输出时序数据动态特性评价能力更强的优点和DDPG算法泛化性能优秀的特点,实现VSC-HVDC系统控制参数优化;最后,通过MATLAB模拟和实验结果验证该方法的有效性。展开更多
基金supported by the Science and Technology Project of State Grid Corporation of China:“Control Strategy Optimization Technology for Large-Scale Photovoltaic Power Generation on the Sending-end and Receiving-end of DC Power System”(4000-201934198A-0-0-00)
文摘The close proximity and the necessity of coordination between multiple high-voltage direct currents(HVDCs)raise the issue of grid partitioning in multi-infeed HVDC systems.A multi-objective partition strategy is proposed in this paper.Several types of relationships to be coordinated and complemented are analyzed and formulated using quantitative indices.According to the graph theory,the HVDC partition is transformed into a graph-cut problem and solved via the spectral clustering algorithm.Finally,the proposed method is validated for a practical multi-HVDC grid,confirming its feasibility and effectiveness.
文摘In multi-infeed HVDC system, the interactions and influences between DC systems AC systems are complex as the electrical distances among DC converter stations which are relatively short. Multi-infeed interaction factor (MIIF) can effectively reflect the interaction among DC systems. The paper theoretically analyzes the impact factors of MIIF like the electrical distances between two DC converter stations and the equivalent impedance of the receiving end AC system. By applying the Kirchhoff’s current law on the inverter AC bus, the paper deduces the analytical expressions for MIIF. From the expression, it is clear how the equivalent impedance of AC system and coupling impedance can affect MIIF. PSCAD simulations validate the effectiveness and the correctness of the proposed expression and some useful conclusions are drawn.
文摘More and more high voltage direct current(HVDC) converters are being located in a load area in the Yangtze River Delta Region in China. It's large transmission capacity and intensive placement are hardly seen in other countries. Accurate and reliable study tools and methods are extremely needed for power system engineers and researchers to deal with such problems which were never met before and otherwhere. A novel approach on electromagnetic modeling of alternating current / direct current(AC/DC) system is proposed and simulation is carried out to replay a real AC 3-phase to ground fault on a multi-infeed high voltage direct current(MIHVDC) system. AC system is specially simplified. Dynamic models and real parameters are adopted in main AC/DC equipments concerned and retained. Modeling and simulation are based on the power system computer aided design/electro-magnetic transient in direct current(PSCAD/EMTDC) system software package.Comparisons between simulation results and the records from the fault recorders are studied including both AC and DC quantities.
基金supported by the State Grid Science and Technology Project 5108-202218280A-2-87-XG.
文摘When multiple LCC-HVDC transmission lines are densely fed into a receiving AC system,voltage dips can easily propagate in the power system,resulting in multiple LCC commutation failures simultaneously.The VSC-HVDC can be used to divide the receiving sys-tem into several interconnected sub-partitions and improve the voltage support capability of the receiving system.Compared with asyn-chronous interconnection,which completely separates the receiving systems with VSC-HVDC,incomplete segmentation with an AC connection is a more pertinent segmenting method for multilayer complex regional power grids.To analyze the voltage support capability of the VSC in incomplete segmentation,a micro-incremental model of the VSC was established,the operating impedance of the VSC was calculated,and the voltage support function of the VSC was quantified.The effect of the fault on the system short-circuit capacity was analyzed,and a calculation method for the multi-infeed short-circuit ratio in an incompletely segmented scenario was obtained.A VSC-segmented model of a two-infeed DC system was built on the EMTDC/PSCAD simulation platform,and the validity of the micro-increment model and accuracy of the proposed conclusions were verified.
基金This work was supported by science and technology project of China Southern Power Grid(No.ZBKJXM20180104).
文摘This paper provides a comprehensive analysis of local and concurrent commutation failure(CF)of multi-infeed high-voltage direct current(HVDC)system considering multi-infeed interaction factor(MIIF).The literature indicates that the local CF is not influenced by MIIF,whereas this paper concludes that both the local CF and concurrent CF are influenced by MIIF.The ability of remote converter to work under reduced reactive power enables its feature to support local converter via inter-connection link.The MIIF measures the strength of electrical connectivity between converters.Higher MIIF gives a clearer path to remote converter to support local converter,but at the same time,it provides an easy path to local converter to disturb remote converter under local fault.The presence of nearby converter increases the local commutation failure immunity index(CFII)while reducing concurrent CFII.Higher MIIF causes reactive power support to flow from remote converter to local converter,which reduces the chances of CF.A mathematical approximation to calculate the increase in local CFII for multi-infeed HVDC configurations is also proposed.A power flow approach is used to model the relation between MIIF and reactive power support from remote end.The local and concurrent CFIIs are found to be inverse to each other over MIIF;therefore,it is recommended that there is an optimal value of MIIF for all converters in close electric proximity to maintain CFII at a certain level.The numerical results of established model are compared with PSCAD/EMTDC simulations.The simulation results show the details of the influence of MIIF on local CF and concurrent CF of multi-infeed HVDC,which validates the analysis presented.
基金supported in part by the National Key Research and Development Program of China(No.2016YFB0900100)part by the National Natural Science Foundation of China(No.51577136)part by the Natural Science Foundation of Hubei Province,China(No.2018CFA080).
文摘High-voltage direct current(HVDC)transmission is playing an increasingly important role in modern power systems,and the resulted power/voltage stability issue has raised widespread concern.This paper presents an on-line power/voltage stability index(PVSI)for multi-infeed HVDC(MIDC)systems.Different from the existing indices which are developed mainly for off-line and static analysis,the proposed PVSI can be applied in real time.Effects of system changes on stability assessment such as change of system states and control strategies are considered.Thus,helpful guidance can be provided for on-line HVDC stability and controls.The PVSI is originally deduced for single-infeed HVDC systems in an‘‘AC way’’by analyzing the power and voltage stability of both pure AC systems and HVDC systems.Moreover,its on-line application in practical MIDC systems is realized by building an equivalent single-infeed model,and utilizing nowadays measurement and communication infrastructures such as wide-area measurement system(WAMS).The effectiveness of the PVSI is verified through simulations in real-time digital simulator(RTDS).
文摘为解决基于模块化多电平换流器的柔性直流输电系统(modular multilevel converter based high voltage direct current,MMC-HVDC)在陆上交流电网故障时出现的盈余功率问题,首先计算验证了能量预警值的合理性,并设计了自适应动作能量值,解决距离和控制转换时延造成子模块过电压的问题;然后分析网侧变流器(grid-side converter,GSC)在低压穿越期间的动态输出特性,提出了基于直流电压变化率反馈的海上换流站精准降压控制用以进行风机减载;最终通过整定协同控制的逻辑与控制参数,提出了一种基于风机精准减载与子模块电容能量协同控制的低电压故障穿越策略,解决故障期间系统能量裕度利用率低与耗能装置投资大的问题。在MATLAB/Simulink中搭建系统仿真模型验证方法有效性,并与现有方法比较。仿真结果表明,所提方法可显著减少甚至避免耗能装置的投入,且具有自适应性,可在不同故障工况下尽可能利用MMC-HVDC系统的能量裕度,尤其在故障程度较轻的工况下,能在故障消除时保留部分能量裕度,有效应对电压二次跌落,提高系统低压穿越能力。
基金This work was supported in part by the State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources(No.LAPS23020).
文摘During the power modulation process of line com-mutated converter-based high-voltage direct current(LCC-HVDC),the transient power mismatch between the fast-change converter station and the slow-response reactive power compen-sators(RPCs)can cause transient voltage disturbances at the weak sending end of the AC grid.To mitigate such voltage dis-turbances,this paper proposes a coordinated feedback power control method for the hybrid multi-infeed HVDC(HMI-HVDC)system comprising an LCC-HVDC and voltage source converter-based HVDC(VSC-HVDC)systems.The mechanism of the disturbance caused by transient power mismatch is quan-titatively analyzed,and the numerical relationship between the instantaneous unbalanced power and the AC voltage is derived.Based on the numerical relationship and considering the time-varying relationship of reactive power between converter sta-tions,the unbalanced power is set as the feedback and coordi-nately distributed among the inverter stations of VSC-HVDC,and the rectifier and the inverter stations of LCC-HVDC.Simu-lation results verify that the proposed method can effectively suppress voltage disturbance without relying on remote commu-nication,thus enhancing the operation performance of the HMI-HVDC system.
文摘高比例、强随机性的可再生能源接入电网常导致交流传输线路过载,同时电力系统升级改造中构建的嵌入式柔性直流输电(voltage source converter based high voltage direct current, VSC-HVDC)系统的可控性没有得到充分利用。为此提出了一种基于功率灵敏度的嵌入式VSC-HVDC紧急控制方法,以快速缓解传输线路过载问题。首先,利用系统模型建立包含嵌入式VSC-HVDC的交流-直流功率灵敏度矩阵。然后,在实时运行中根据推导的灵敏度矩阵调整VSC-HVDC的有功功率,以应对特定的交流电网过载。在调整过程中,采用优化控制方法确保直流调整的总量最小化,同时交流线路有功功率保持在可接受的范围内。最后,通过修改的IEEE39节点系统仿真验证了该方法在多种故障工况下的有效性,可快速缓解交流线路过载并保证全网运行安全。
文摘随着电网换相型高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)技术的广泛应用,交直流混联电网的谐波交互问题愈加复杂,建立LCC-HVDC小信号模型是分析换流器交直流谐波耦合特性的重要手段。为此,基于谐波状态空间理论(harmonic state space, HSS)建立双端12脉动LCC-HVDC小信号模型,不仅考虑了LCC谐波传递特性,还考虑了换流变压器联结方式、控制链路延时等因素的影响。采用模块化思想分别建立各子系统谐波状态空间模型,通过接口矩阵连接为整体,使得LCC的谐波状态空间建模在易于扩展的同时,提高了精确度。最后,给出交直流谐波传递的具体表达式,并通过PSCAD仿真验证模型的准确性。所建模型不仅为后续扩展或接入更为复杂的系统奠定了基础,还可应用于双端LCC系统谐波交互稳定性评估和系统参数优化设计。
基金supported by the National Key Research and Development Program of China(No.2021YFB1507001).
文摘During sending-end faults in the hybrid cascaded HVDC(HC-HVDC)system,the transient voltage drop characteristics under the interaction of the AC/DC hybrid system remain unclear,and the reactive power support provided by the HC-HVDC to the sending-end AC system requires further investigation.To address this problem,the reactive power interaction coupling mechanism between the sending-end AC system and the HC-HVDC is revealed,and the transient voltage mathematical model considering fault severity and duration is established.Under the dynamic change of the AC system voltage,the difference between the reactive power provided only by the reactive power compensation devices and by the combined modular multilevel converters(MMC)and reactive power compensation devices is analyzed.It is concluded that using MMC to provide a proportion of reactive power enhances the reactive power support to the AC system during faults.Then,the transient voltage model considering the reactive power support of MMC is established,and the critical reactive power consumption of line commutated converter(LCC)is quantified.It is concluded that the reactive power consumption of LCC exceeding its critical value deteriorates the transient voltage.A coordinated support strategy for the sending-end AC system based on reactive power support of MMC and reactive power regulation of LCC is proposed.It can effectively address the challenge of weakened reactive power support to the AC system due to voltage drop,thereby preventing the unbalanced reactive power from deteriorating the transient voltage,and realizing active support of the tran-sient voltage.Finally,a simulation model is established on the PSCAD/EMTDC platform,and the simulation results validate the effectiveness of the proposed strategy in supporting the transient voltage,under different fault types,durations,severities,and locations.
文摘针对柔性直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)控制参数设计过程中存在的鲁棒性差、依赖已知电路参数、工程设计经验化等问题,提出一种基于马尔科夫转换场(Markov transition field,MTF)与深度确定性策略梯度算法(deep deterministic policy gradient,DDPG)结合的鲁棒性强、不依赖电路参数特性以及可视化的VSC-HVDC控制参数优化设计方法。首先,采用马尔科夫转换场将电路功率、电压等一维时序波形数据转换为二维马尔科夫转换场域图像并使用马尔科夫转换场损失函数(Markov transition field loss,MTFL)判断二维转换域图的数据波动性;其次,将MTFL损失函数与DDPG算法相结合,综合利用MTFL损失函数对系统输出时序数据动态特性评价能力更强的优点和DDPG算法泛化性能优秀的特点,实现VSC-HVDC系统控制参数优化;最后,通过MATLAB模拟和实验结果验证该方法的有效性。
