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
Adenomyosis (AD) refers to the endometrium (including glands and stroma) into myometrium gr owth of pathological changes, with the delay of women's childbea ring age, the pa ti ents with AD-associated infertility ...Adenomyosis (AD) refers to the endometrium (including glands and stroma) into myometrium gr owth of pathological changes, with the delay of women's childbea ring age, the pa ti ents with AD-associated infertility increased significantly. Although scholars disagreed about the effect of AD on infertility, more and more evidence showed that AD was closely related to the str uct ural and func ti onal defects of the eutopic endomet rium and myomet rial junc tional zone (MJZ), which may lead to embryo implantation failure and infertility. With the rapid development of imaging technology, the accuracy of diagnose AD has been enhanced, more and more infertility patients were diagnosed with AD. At the same time, a series of pathogenic hypothesis have been proposed to explain the relationship between AD. In addition, AD may influence the patient's reproductive function by affecting sperm transport, embryo implantation, altering uterine peristalsis, influencing the structure and function of endometrium, and changing the intrauterine environment. At present, the treatment of AD-associated infertility is similar to the treatment of AD. The commonly used treatment methods include drug therapy, conservative operative treatment, drug combination surgery, and Chinese medicine treatment and so on. The clinical and experimental studies of AD complicated with infertility and its possible pathogenesis and treatment in recent years are reviewed in this article.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
多馈入直流(multi-infeed direct current,MIDC)系统换相失败抵御能力的评价与提升方法,对实际电网系统换相失败特性的测试、评估难题的解决以及换相失败防御技术在电网规划与运行中的应用具有重要意义,因此文中对其进行系统科学的归纳...多馈入直流(multi-infeed direct current,MIDC)系统换相失败抵御能力的评价与提升方法,对实际电网系统换相失败特性的测试、评估难题的解决以及换相失败防御技术在电网规划与运行中的应用具有重要意义,因此文中对其进行系统科学的归纳和总结。首先,阐述MIDC系统以及换相失败的基本定义,分析不同类型故障对换相失败的影响,梳理其关键影响因素,并总结现有换相失败判据;其次,综述目前已有的换相失败抵御能力评价方法;然后,从无功补偿优化、控制保护优化以及换流器拓扑改进等3个方面对现阶段MIDC系统换相失败抵御能力提升方法进行综述;最后,明确了未来需要重点关注以下方向:采用归一化的效果评价方式,在具备标准意义的仿真平台上开展可重复的校检,形成系统性、综合性的换相失败抵御能力评价方法,并提出包括换流站级、换流器级和系统级的多层次协同提升策略。展开更多
Due to increased penetration of renewable energies,DC links and other emerging technologies,power system operation and planning have to cope with various uncertainties and risks.In order to solve the problems of excee...Due to increased penetration of renewable energies,DC links and other emerging technologies,power system operation and planning have to cope with various uncertainties and risks.In order to solve the problems of exceeding short circuit current and multi-infeed DC interaction,a coordinated optimization method is presented in this paper.Firstly,a branch selection strategy is proposed by analyzing the sensitivity relationship between current limiting measures and the impedance matrix.Secondly,the impact of network structure changes on the multi-infeed DC system is derived.Then the coordinated optimization model is established,which considers the cost and effect of current limiting measures,the tightness of network structure and the voltage support capability of AC system to multiple DCs.Finally,the non-dominated sorting genetic algorithm II combining with the branch selection strategy,is used to find the Pareto optimal schemes.Case studies on a planning power system demonstrated the feasibility and speediness of this method.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
基于电网换相换流器(line commutation converter,LCC)的特高压直流输电系统(ultra-high voltage direct current,UHVDC)是远距离大容量输电的主要技术手段。为尽可能避免系统稳定裕度不足带来的直流降功率事件,提出一种频率偏差与电压...基于电网换相换流器(line commutation converter,LCC)的特高压直流输电系统(ultra-high voltage direct current,UHVDC)是远距离大容量输电的主要技术手段。为尽可能避免系统稳定裕度不足带来的直流降功率事件,提出一种频率偏差与电压刚度约束下的多直流馈入受端电网优化调度方法。首先,基于一次调频模型,推导出频率稳定性对系统中最大直流输送功率的约束条件;其次,提出评价多直流同时换相失败恢复特性的电压刚度指标,并基于该指标建立多直流馈入受端电网的电压稳定约束;然后,综合考虑频率和电压稳定约束以及多种运行约束的情况下,建立多直流馈入受端电网优化调度模型;最后,在一个改进的IEEE 39节点系统中进行测试。结果表明,所提方法能够通过改变开机方式和直流功率,保证系统频率和电压稳定性满足要求,避免强直弱交带来的安全稳定风险。展开更多
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Adenomyosis (AD) refers to the endometrium (including glands and stroma) into myometrium gr owth of pathological changes, with the delay of women's childbea ring age, the pa ti ents with AD-associated infertility increased significantly. Although scholars disagreed about the effect of AD on infertility, more and more evidence showed that AD was closely related to the str uct ural and func ti onal defects of the eutopic endomet rium and myomet rial junc tional zone (MJZ), which may lead to embryo implantation failure and infertility. With the rapid development of imaging technology, the accuracy of diagnose AD has been enhanced, more and more infertility patients were diagnosed with AD. At the same time, a series of pathogenic hypothesis have been proposed to explain the relationship between AD. In addition, AD may influence the patient's reproductive function by affecting sperm transport, embryo implantation, altering uterine peristalsis, influencing the structure and function of endometrium, and changing the intrauterine environment. At present, the treatment of AD-associated infertility is similar to the treatment of AD. The commonly used treatment methods include drug therapy, conservative operative treatment, drug combination surgery, and Chinese medicine treatment and so on. The clinical and experimental studies of AD complicated with infertility and its possible pathogenesis and treatment in recent years are reviewed in this article.
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.
文摘多馈入直流(multi-infeed direct current,MIDC)系统换相失败抵御能力的评价与提升方法,对实际电网系统换相失败特性的测试、评估难题的解决以及换相失败防御技术在电网规划与运行中的应用具有重要意义,因此文中对其进行系统科学的归纳和总结。首先,阐述MIDC系统以及换相失败的基本定义,分析不同类型故障对换相失败的影响,梳理其关键影响因素,并总结现有换相失败判据;其次,综述目前已有的换相失败抵御能力评价方法;然后,从无功补偿优化、控制保护优化以及换流器拓扑改进等3个方面对现阶段MIDC系统换相失败抵御能力提升方法进行综述;最后,明确了未来需要重点关注以下方向:采用归一化的效果评价方式,在具备标准意义的仿真平台上开展可重复的校检,形成系统性、综合性的换相失败抵御能力评价方法,并提出包括换流站级、换流器级和系统级的多层次协同提升策略。
基金This work was supported by State Grid Corporation of China,Major Projects on Planning and Operation Control of Large Scale Grid under Grant SGCC-MPLG020-2012.
文摘Due to increased penetration of renewable energies,DC links and other emerging technologies,power system operation and planning have to cope with various uncertainties and risks.In order to solve the problems of exceeding short circuit current and multi-infeed DC interaction,a coordinated optimization method is presented in this paper.Firstly,a branch selection strategy is proposed by analyzing the sensitivity relationship between current limiting measures and the impedance matrix.Secondly,the impact of network structure changes on the multi-infeed DC system is derived.Then the coordinated optimization model is established,which considers the cost and effect of current limiting measures,the tightness of network structure and the voltage support capability of AC system to multiple DCs.Finally,the non-dominated sorting genetic algorithm II combining with the branch selection strategy,is used to find the Pareto optimal schemes.Case studies on a planning power system demonstrated the feasibility and speediness of this method.
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).
文摘基于电网换相换流器(line commutation converter,LCC)的特高压直流输电系统(ultra-high voltage direct current,UHVDC)是远距离大容量输电的主要技术手段。为尽可能避免系统稳定裕度不足带来的直流降功率事件,提出一种频率偏差与电压刚度约束下的多直流馈入受端电网优化调度方法。首先,基于一次调频模型,推导出频率稳定性对系统中最大直流输送功率的约束条件;其次,提出评价多直流同时换相失败恢复特性的电压刚度指标,并基于该指标建立多直流馈入受端电网的电压稳定约束;然后,综合考虑频率和电压稳定约束以及多种运行约束的情况下,建立多直流馈入受端电网优化调度模型;最后,在一个改进的IEEE 39节点系统中进行测试。结果表明,所提方法能够通过改变开机方式和直流功率,保证系统频率和电压稳定性满足要求,避免强直弱交带来的安全稳定风险。
