Multiterminal hybrid HVDC systems,combining the advantages of conventional and flexible DC systems,are considered important development trends for future power networks.With the ability to suppress DC fault current,hy...Multiterminal hybrid HVDC systems,combining the advantages of conventional and flexible DC systems,are considered important development trends for future power networks.With the ability to suppress DC fault current,hybrid HVDC systems eliminate the requirement of current limiting reactors at both ends of DC lines.Thus,non-unit protection based on line boundaries is no longer applicable.In this paper,a non-unit protection scheme in cooperation with converter control is proposed to ensure protection speed,reliability,and sen-sitivity for multiterminal hybrid HVDC systems without line boundaries.In the proposed protection scheme,the protection criterion based on the transient energy of the DC voltage and the direction criterion based on the travelling wave are used to identify whether the fault occurs on the DC line.When the fault is detected as a DC-line fault,the relevant converter station is quickly blocked.After a specified hold-off duration,the converter station interfacing with multiple DC lines is prioritized for restart,while the remaining converter stations are restarted once the DC voltage is stabilized.Simulations based on PSCAD/EMTDC validate the feasibility of the proposed protection scheme and its superiority over competing approaches.展开更多
In this paper, we first give the definition of possibly non-unital function system, which is a characterization of the self-adjoint subspace of the space of continuous functions on a compact Hausdorff space with the i...In this paper, we first give the definition of possibly non-unital function system, which is a characterization of the self-adjoint subspace of the space of continuous functions on a compact Hausdorff space with the induced order and norm structure. Similar to operator system case, we define the unitalization of a possibly non-unital function system. Then we construct two possibly non-unital operator system structures on a given possibly non-unital function system, which are the analogues of minimal and maximal operator spaces on a normed space. These two structures have many interesting relations with the minimal and maximal operator system structures on a given function system.展开更多
An analytical method of fault characteristic for the HVDC system based on frequency response characteristics of boundary elements is presented here.The computational formulas of transfer function and input impedance a...An analytical method of fault characteristic for the HVDC system based on frequency response characteristics of boundary elements is presented here.The computational formulas of transfer function and input impedance are deduced using the distributed parameter model of HVDC transmission line,and the amplitude-to-frequency-characteristics of the transfer function and input impedance are analyzed.Based on the amplitude-to-frequency difference between internal and external faults,a non-unit protection method for VSC-HVDC transmission line is presented.Using the current ratio of high-to-low-frequency,this protection method can distinguish internal from external fault.The presented algorithm only uses local-end current,has high operation speed,and is easy to implement.Simulations on a±200 kV VSC-HVDC system are conducted to demonstrate the validity and feasibility of the developed protection method.展开更多
目的调查新生儿重症监护病房(neonatal intensive care unit,NICU)无创呼吸机通气患儿肠内营养喂养不耐受(feeding intolerance,FI)发生状况,分析FI的影响因素,为预防FI提供参考依据。方法收集2022年1月—2024年3月乌鲁木齐某三级甲等医...目的调查新生儿重症监护病房(neonatal intensive care unit,NICU)无创呼吸机通气患儿肠内营养喂养不耐受(feeding intolerance,FI)发生状况,分析FI的影响因素,为预防FI提供参考依据。方法收集2022年1月—2024年3月乌鲁木齐某三级甲等医院NICU的172例接受无创呼吸机通气患儿作为研究对象,回顾性分析临床资料,观察FI发生率。根据是否发生FI,分为FI组和非FI组,采用Logistic回归分析FI影响因素,绘制受试者工作曲线(receiver operating characteristic,ROC)评价Logistic回归模型对FI的预测价值。结果172例患儿中,64例(37.2%)发生FI。FI组早产儿比例、新生儿呼吸窘迫综合征(neonatal respiratory distress syndrome,NRDS)比例、急性生理与慢性健康Ⅱ(Acute Physiology and Chronic Health EvaluationⅡ,APACHEⅡ)评分、开始首次肠内营养时间、经鼻间歇正压通气比例、腹内压和使用镇静药物比例高于非FI组(P<0.05)。Logistic回归显示,早产儿(OR=5.516)、NRDS(OR=4.242)、APACHEⅡ评分(OR=1.797)、开始首次肠内营养时间(OR=1.163)、经鼻间歇正压通气(OR=4.029)、腹内压(OR=2.017)和使用镇静药物(OR=4.247)均是NICU接受无创呼吸机通气患儿FI的独立危险因素(P<0.05)。ROC分析显示,Logistic回归模型预测FI的曲线下面积为0.974,灵敏度为96.9%,特异度为91.7%,预测效果良好。结论NICU接受无创呼吸机通气患儿具有较高的肠内营养FI发生率,早产儿、NRDS、APACHEⅡ评分、开始首次肠内营养时间、经鼻间歇正压通气、腹内压和使用镇静药物是其危险因素。对于存在上述FI危险因素的患儿,应及早干预并尽早开始肠内营养支持,选择合适的通气模式,尽量避免或减少镇静药物的使用。展开更多
基金supported by the National Natural Science Foundation of China(No.52207088)the Natural Science Foundation of Hebei Province(No.E2024202184).
文摘Multiterminal hybrid HVDC systems,combining the advantages of conventional and flexible DC systems,are considered important development trends for future power networks.With the ability to suppress DC fault current,hybrid HVDC systems eliminate the requirement of current limiting reactors at both ends of DC lines.Thus,non-unit protection based on line boundaries is no longer applicable.In this paper,a non-unit protection scheme in cooperation with converter control is proposed to ensure protection speed,reliability,and sen-sitivity for multiterminal hybrid HVDC systems without line boundaries.In the proposed protection scheme,the protection criterion based on the transient energy of the DC voltage and the direction criterion based on the travelling wave are used to identify whether the fault occurs on the DC line.When the fault is detected as a DC-line fault,the relevant converter station is quickly blocked.After a specified hold-off duration,the converter station interfacing with multiple DC lines is prioritized for restart,while the remaining converter stations are restarted once the DC voltage is stabilized.Simulations based on PSCAD/EMTDC validate the feasibility of the proposed protection scheme and its superiority over competing approaches.
文摘In this paper, we first give the definition of possibly non-unital function system, which is a characterization of the self-adjoint subspace of the space of continuous functions on a compact Hausdorff space with the induced order and norm structure. Similar to operator system case, we define the unitalization of a possibly non-unital function system. Then we construct two possibly non-unital operator system structures on a given possibly non-unital function system, which are the analogues of minimal and maximal operator spaces on a normed space. These two structures have many interesting relations with the minimal and maximal operator system structures on a given function system.
基金supported in part by the Science and Technology Project Funds through Grid State Corporation(Grant No.SGSNKYOOKJJS1501564)the National Science Foundation of China(Grant No.51477131).
文摘An analytical method of fault characteristic for the HVDC system based on frequency response characteristics of boundary elements is presented here.The computational formulas of transfer function and input impedance are deduced using the distributed parameter model of HVDC transmission line,and the amplitude-to-frequency-characteristics of the transfer function and input impedance are analyzed.Based on the amplitude-to-frequency difference between internal and external faults,a non-unit protection method for VSC-HVDC transmission line is presented.Using the current ratio of high-to-low-frequency,this protection method can distinguish internal from external fault.The presented algorithm only uses local-end current,has high operation speed,and is easy to implement.Simulations on a±200 kV VSC-HVDC system are conducted to demonstrate the validity and feasibility of the developed protection method.
文摘目的调查新生儿重症监护病房(neonatal intensive care unit,NICU)无创呼吸机通气患儿肠内营养喂养不耐受(feeding intolerance,FI)发生状况,分析FI的影响因素,为预防FI提供参考依据。方法收集2022年1月—2024年3月乌鲁木齐某三级甲等医院NICU的172例接受无创呼吸机通气患儿作为研究对象,回顾性分析临床资料,观察FI发生率。根据是否发生FI,分为FI组和非FI组,采用Logistic回归分析FI影响因素,绘制受试者工作曲线(receiver operating characteristic,ROC)评价Logistic回归模型对FI的预测价值。结果172例患儿中,64例(37.2%)发生FI。FI组早产儿比例、新生儿呼吸窘迫综合征(neonatal respiratory distress syndrome,NRDS)比例、急性生理与慢性健康Ⅱ(Acute Physiology and Chronic Health EvaluationⅡ,APACHEⅡ)评分、开始首次肠内营养时间、经鼻间歇正压通气比例、腹内压和使用镇静药物比例高于非FI组(P<0.05)。Logistic回归显示,早产儿(OR=5.516)、NRDS(OR=4.242)、APACHEⅡ评分(OR=1.797)、开始首次肠内营养时间(OR=1.163)、经鼻间歇正压通气(OR=4.029)、腹内压(OR=2.017)和使用镇静药物(OR=4.247)均是NICU接受无创呼吸机通气患儿FI的独立危险因素(P<0.05)。ROC分析显示,Logistic回归模型预测FI的曲线下面积为0.974,灵敏度为96.9%,特异度为91.7%,预测效果良好。结论NICU接受无创呼吸机通气患儿具有较高的肠内营养FI发生率,早产儿、NRDS、APACHEⅡ评分、开始首次肠内营养时间、经鼻间歇正压通气、腹内压和使用镇静药物是其危险因素。对于存在上述FI危险因素的患儿,应及早干预并尽早开始肠内营养支持,选择合适的通气模式,尽量避免或减少镇静药物的使用。
