The face velocities of the high efficiency particulate air filters and the ultra low penetration airfilters in fan filter units (FFUs) have large relative standard deviation and turbulivity. It seriously affects the ...The face velocities of the high efficiency particulate air filters and the ultra low penetration airfilters in fan filter units (FFUs) have large relative standard deviation and turbulivity. It seriously affects the unidirectivity of the flow in the unidirectional flow clean zone and cleanroom. The cross contamination in this kind of unidirectional flow area is hardly controlled. It is significant to find optional method for keeping the face velocity uniformity of FFU and reducing the face velocity turbulivity of FFU, furthermore, to keep the cleanliness level under FFUs. The normal and easy method is to add flow rectifiers under filters. FFUs with various flow rectifiers have been tested. The uniformity and turbulivity of facevelocity under the FFU are presented in this paper. The influence of the facevelocity uniformity and turbulivity on the contamination boundary of the unidirectional flow is studiedas well.展开更多
The Auto-Transformer Rectifier Unit（ATRU） is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, t...The Auto-Transformer Rectifier Unit（ATRU） is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, the ATRU has become a preferred AC/DC solution to supply power to the electric environment control system on-board future aircraft. In this paper, a general modelling method for ATRUs is introduced. The developed model is based on the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs. In this paper, we carry on our research in modelling symmetric 18-pulse ATRUs and develop a generic modelling technique. The developed generic model can study not only symmetric but also asymmetric ATRUs. An 18-pulse asymmetric ATRU is used to demonstrate the accuracy and efficiency of the developed model by comparing with corresponding detailed switching SABER models provided by our industrial partner. The functional models also allow accelerated and accurate simulations and thus enable whole-scale more-electric aircraft electrical power system studies in the future.展开更多
To solve the problem of harmonic pollution to the power grid that caused by traditional diode rectifier and phase controlled rectifier, the unit power factor PWM rectifier is designed. The topology structure of the re...To solve the problem of harmonic pollution to the power grid that caused by traditional diode rectifier and phase controlled rectifier, the unit power factor PWM rectifier is designed. The topology structure of the rectifier circuit is introduced and the double closed-loop control strategy in three-phase stationary coordinate system is analyzed. For the deficiency of control strategy, the control strategy in two-phase synchronous rotating coordinate system is proposed. This makes the independent control of active current and reactive current to be realized. The simulation model of the PWM rectifier is built and the effectiveness of the control method proposed in this paper is verified by simulation.展开更多
Natural regeneration is the basis of a dynamic and demographic balance of plant populations. The objective of this study was to assess the natural regeneration potential of woody species along secondary roads post-log...Natural regeneration is the basis of a dynamic and demographic balance of plant populations. The objective of this study was to assess the natural regeneration potential of woody species along secondary roads post-logging abandoned since 2008 and 2018. In the two Annual Allowable Cuts (AAC 2008 and AAC 2018), 24 regenerating sub-plots (i.e. 12 sub-plots for AAC 2008 and 12 sub-plots for AAC 2018) with a unit area of 5 m × 5 m were delimited with a total area of 0.06 ha (i.e. 0.03 ha for each AAC). The abundance and diversity of woody species were respectively inventoried and estimated. Two estimators of the specific richness were used to estimate the floristic diversity of each Annual Allowable Cuts (AAC). The results reveal globally 88 woody species in the AAC 2008 and 241 woody species in the AAC 2018, with respective average densities of 2933 stem/ha and 8033 stem/ha. There was a very highly significant difference between the mean densities of the two AAC (Kruskal-Wallis test;H = 2.36, p-value < 0.000). The results also highlight a great diversity and a relatively high abundance of woody species in the 2018 AAC compared to the 2008 AAC. Also, the spatial structuring of the sub-plots on the basis of Principal Component Analysis (PCA) demonstrates that the floristic composition of the two AAC is globally different. The study suggests silvicultural interventions and the long-term assessment of regenerating woody species along abandoned secondary roads in order to guarantee the sustainable management of their population.展开更多
将二极管整流单元(diode rectifier unit,DRU)与模块化多电平变换器(modular multilevel converter,MMC)背靠背连接组成交-交变流器并应用于低频交流(low frequency alternative current,LFAC)输电系统中,是降低海上风电送出成本的重要...将二极管整流单元(diode rectifier unit,DRU)与模块化多电平变换器(modular multilevel converter,MMC)背靠背连接组成交-交变流器并应用于低频交流(low frequency alternative current,LFAC)输电系统中,是降低海上风电送出成本的重要技术路线之一。针对该系统中谐波含量过高的问题,提出了一种低成本谐波抑制方法。首先,对DRU-LFAC系统的谐波特性进行了分析,并在此基础上提出一种新型交流侧电流谐波抑制策略。所提策略通过在正负极直流线路中注入特定的电流谐波以实现对交流侧电流谐波的抑制。同时,直流侧谐波电流的通路由双极性背靠背DRU-MMC的中性线提供。随后,对所提策略产生的额外运行损耗进行了定量计算,并与常规滤波方法进行了经济性对比分析;最后,通过PSCAD/EMTDC仿真和远宽StarSim控制器硬件在环实验验证了所提谐波抑制策略的有效性。研究结果表明:所提策略相较于常规滤波方法在海上风电工程的整个生命周期内能降低约70%的滤波成本,且能够有效降低系统交流侧电流的总谐波失真(total harmonic distortion,THD)。展开更多
This paper presents a frequency support strategy for the diode rectifier unit(DRU)-high-voltage direct current(HVDC)-based offshore wind power integration system,which coordinates multiple power sources without commun...This paper presents a frequency support strategy for the diode rectifier unit(DRU)-high-voltage direct current(HVDC)-based offshore wind power integration system,which coordinates multiple power sources without communication to reduce receiving grid frequency fluctuations.First,based on the deduced DRU's frequency transfer characteristic,a fine-designed ripple carrying frequency information is superimposed on the HVDC link,transferring the onshore frequency to offshore wind turbines(WTs)via the DC ripple and coupled AC harmonic without communication.Second,multiple power sources are utilized for frequency support,including HVDC capacitance and grid-forming WTs combined with energy storage systems,and appropriate sources are activated in the order specified by the designed thresholds.Finally,the effectiveness of the proposed frequency support strategy is verified by simulations in PSCAD/EMTDC.展开更多
This study analyzes the stability and reactive characteristics of the hybrid offshore wind farm that includes gridforming(GFM)and grid-following(GFL)wind turbines(WTs)integrated with a diode rectifier unit(DRU)based h...This study analyzes the stability and reactive characteristics of the hybrid offshore wind farm that includes gridforming(GFM)and grid-following(GFL)wind turbines(WTs)integrated with a diode rectifier unit(DRU)based high-voltage direct current(HVDC)system.The determination method for the proportion of GFM WTs is proposed while considering system stability and optimal offshore reactive power constraints.First,the small-signal stability is studied based on the developed linear model,and crucial factors that affect the stability are captured by eigenvalue analysis.The reactive power-frequency compensation control of GFM WTs is then proposed to improve the reactive power and frequency dynamics.Second,the relationship between offshore reactive power imbalance and the effectiveness of GFM capability is analyzed.Offshore reactive power optimization methods are next proposed to diminish offshore reactive load.These methods include the optimal design for the reactive capacity of the AC filter and the reactive power compensation control of GFL WTs.Third,in terms of stability and optimal offshore reactive power constraints,the principle and calculation method for determining the proportion of GFM WTs are proposed,and the critical proportion of GFM WTs is determined over the full active power range.Finally,case studies using a detailed model are conducted by timedomain simulations in PSCAD/EMTDC.The simulations verify the theoretical analysis results and the effectiveness of the proposed determination method for the proportion of GFM WTs and reactive power optimization methods.展开更多
The accurate state of health(SOH)estimation in lithium-ion batteries represents a critical technological challenge with profound implications for electric vehicle performance and user experience.Precise SOH assessment...The accurate state of health(SOH)estimation in lithium-ion batteries represents a critical technological challenge with profound implications for electric vehicle performance and user experience.Precise SOH assessment not only enables reliable mileage prediction but also ensures operational safety.However,the complex and non-linear capacity fading process during battery cycling poses a challenge to obtaining accurate SOH.To address this issue,this study proposes an effective health factor derived from the local voltage range during the battery charging phase.First,the battery charging phase is divided evenly with reference to voltage intervals,and an importance analysis is conducted on each voltage interval.From these,the voltage interval with the strongest correlation to State of Health(SOH)is extracted as the feature interval.Then,a data-driven framework integrating variational mode decomposition(VMD)with gated recurrent unit(GRU)neural networks enables comprehensive multi-scale temporal feature analysis for enhanced SOH estimation.The methodology begins with rigorous feature engineering to identify and extract optimal health indicators demonstrating superior correlation.Subsequently,the VMD algorithm performs sophisticated signal processing to decompose both the measured capacity and derived health indicators into their constituent intrinsic mode functions and residual components.Finally,a GRU-based neural network is implemented to establish a robust SOH estimation model.Experimental validation using cycling data from different datasets shows that the root mean square error of the estimation results is consistently below 3%,demonstrating the good accuracy and generalisation of the proposed method,using only local data from the charging phase.展开更多
Previous studies have shown that models of depression exhibit structural and functional changes to the neurovascular unit. Thus, we hypothesized that diabetes-related depression might be associated with damage to the ...Previous studies have shown that models of depression exhibit structural and functional changes to the neurovascular unit. Thus, we hypothesized that diabetes-related depression might be associated with damage to the hippocampal neurovascular unit. To test this hypothesis, neurons, astrocytes and endothelial cells were isolated from the brain tissues of rat embryos and newborn rats. Hippocampal neurovascular unit co-cultures were produced using the Transwell chamber co-culture system. A model of diabetes-related depression was generated by adding 150 mM glucose and 200 μM corticosterone to the culture system and compared with the neuron + astrocyte and astrocyte + endothelial cell co-culture systems. Western blot assay was used to measure levels of structural proteins in the hippocampal neurovascular unit co-culture system. Levels of basic fibroblast growth factor, angiogenic factor 1, glial cell line–derived neurotrophic factor, transforming growth factor β1, leukemia inhibitory factor and 5-hydroxytryptamine in the hippocampal neurovascular unit co-culture system were measured by enzyme-linked immunosorbent assay. Flow cytometry and terminal deoxynucleotidyl transferase(TdT)-mediated dUTP nick end labeling staining was used to assess neuronal apoptosis in the hippocampal neurovascular unit. The neurovascular unit triple cell co-culture system had better barrier function and higher levels of structural and secretory proteins than the double cell co-culture systems. In comparison, in the model of diabetes-related depression, the neurovascular unit was damaged with decreased barrier function, poor structural integrity and impaired secretory function. Moreover, neuronal apoptosis was markedly increased, and 5-hydroxytryptamine levels were reduced. These results suggest that diabetes-related depression is associated with structural and functional damage to the neurovascular unit. Our findings provide a foundation for further studies on the pathogenesis of diabetes-related depression.展开更多
Houshiheisan is composed of wind-dispelling （chrysanthemun fower, divaricate saposhnikovia root, Manchurian wild ginger, cassia twig, Szechwan lovage rhizome, and platycodon root） and deficiency-nourishing （ginseng...Houshiheisan is composed of wind-dispelling （chrysanthemun fower, divaricate saposhnikovia root, Manchurian wild ginger, cassia twig, Szechwan lovage rhizome, and platycodon root） and deficiency-nourishing （ginseng, Chinese angelica, large-head atractylodes rhizome, Indian bread, and zingiber） drugs. In this study, we assumed these drugs have protective effects against cerebral ischemia, on neurovascular units. Houshiheisan was intragastrically administered in a rat model of focal cerebral ischemia. Hematoxylin-eosin staining, transmission electron microscopy, immu- nofluorescence staining, and western blot assays showed that Houshiheisan reduced pathological injury to the ischemic penumbra, protected neurovascular units, visibly up-regtflated neuronal nuclear antigen expression, and down-regulated amyloid precursor protein and amyloid-[3 42 expression. Wind-dispelling and deficiency-nourishing drugs maintained NeuN expression to varying degrees, but did not affect amyloid precursor protein or amyloid-~ 42 expression in the ischemic penumbra. Our results suggest that the compound prescription Houshiheisan effectively suppresses abnormal amyloid precursor protein accumulation, reduces amyloid substance depo- sition, maintains stabilization of the internal environment of neurovascular units, and minimizes injury to neurovascular units in the ischemic penumbra.展开更多
文摘The face velocities of the high efficiency particulate air filters and the ultra low penetration airfilters in fan filter units (FFUs) have large relative standard deviation and turbulivity. It seriously affects the unidirectivity of the flow in the unidirectional flow clean zone and cleanroom. The cross contamination in this kind of unidirectional flow area is hardly controlled. It is significant to find optional method for keeping the face velocity uniformity of FFU and reducing the face velocity turbulivity of FFU, furthermore, to keep the cleanliness level under FFUs. The normal and easy method is to add flow rectifiers under filters. FFUs with various flow rectifiers have been tested. The uniformity and turbulivity of facevelocity under the FFU are presented in this paper. The influence of the facevelocity uniformity and turbulivity on the contamination boundary of the unidirectional flow is studiedas well.
文摘The Auto-Transformer Rectifier Unit（ATRU） is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, the ATRU has become a preferred AC/DC solution to supply power to the electric environment control system on-board future aircraft. In this paper, a general modelling method for ATRUs is introduced. The developed model is based on the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs. In this paper, we carry on our research in modelling symmetric 18-pulse ATRUs and develop a generic modelling technique. The developed generic model can study not only symmetric but also asymmetric ATRUs. An 18-pulse asymmetric ATRU is used to demonstrate the accuracy and efficiency of the developed model by comparing with corresponding detailed switching SABER models provided by our industrial partner. The functional models also allow accelerated and accurate simulations and thus enable whole-scale more-electric aircraft electrical power system studies in the future.
文摘To solve the problem of harmonic pollution to the power grid that caused by traditional diode rectifier and phase controlled rectifier, the unit power factor PWM rectifier is designed. The topology structure of the rectifier circuit is introduced and the double closed-loop control strategy in three-phase stationary coordinate system is analyzed. For the deficiency of control strategy, the control strategy in two-phase synchronous rotating coordinate system is proposed. This makes the independent control of active current and reactive current to be realized. The simulation model of the PWM rectifier is built and the effectiveness of the control method proposed in this paper is verified by simulation.
文摘Natural regeneration is the basis of a dynamic and demographic balance of plant populations. The objective of this study was to assess the natural regeneration potential of woody species along secondary roads post-logging abandoned since 2008 and 2018. In the two Annual Allowable Cuts (AAC 2008 and AAC 2018), 24 regenerating sub-plots (i.e. 12 sub-plots for AAC 2008 and 12 sub-plots for AAC 2018) with a unit area of 5 m × 5 m were delimited with a total area of 0.06 ha (i.e. 0.03 ha for each AAC). The abundance and diversity of woody species were respectively inventoried and estimated. Two estimators of the specific richness were used to estimate the floristic diversity of each Annual Allowable Cuts (AAC). The results reveal globally 88 woody species in the AAC 2008 and 241 woody species in the AAC 2018, with respective average densities of 2933 stem/ha and 8033 stem/ha. There was a very highly significant difference between the mean densities of the two AAC (Kruskal-Wallis test;H = 2.36, p-value < 0.000). The results also highlight a great diversity and a relatively high abundance of woody species in the 2018 AAC compared to the 2008 AAC. Also, the spatial structuring of the sub-plots on the basis of Principal Component Analysis (PCA) demonstrates that the floristic composition of the two AAC is globally different. The study suggests silvicultural interventions and the long-term assessment of regenerating woody species along abandoned secondary roads in order to guarantee the sustainable management of their population.
文摘将二极管整流单元(diode rectifier unit,DRU)与模块化多电平变换器(modular multilevel converter,MMC)背靠背连接组成交-交变流器并应用于低频交流(low frequency alternative current,LFAC)输电系统中,是降低海上风电送出成本的重要技术路线之一。针对该系统中谐波含量过高的问题,提出了一种低成本谐波抑制方法。首先,对DRU-LFAC系统的谐波特性进行了分析,并在此基础上提出一种新型交流侧电流谐波抑制策略。所提策略通过在正负极直流线路中注入特定的电流谐波以实现对交流侧电流谐波的抑制。同时,直流侧谐波电流的通路由双极性背靠背DRU-MMC的中性线提供。随后,对所提策略产生的额外运行损耗进行了定量计算,并与常规滤波方法进行了经济性对比分析;最后,通过PSCAD/EMTDC仿真和远宽StarSim控制器硬件在环实验验证了所提谐波抑制策略的有效性。研究结果表明:所提策略相较于常规滤波方法在海上风电工程的整个生命周期内能降低约70%的滤波成本,且能够有效降低系统交流侧电流的总谐波失真(total harmonic distortion,THD)。
基金supported by the State Grid Corporation of China Science and Technology Project(No.5500-202319103A-1-1-ZN).
文摘This paper presents a frequency support strategy for the diode rectifier unit(DRU)-high-voltage direct current(HVDC)-based offshore wind power integration system,which coordinates multiple power sources without communication to reduce receiving grid frequency fluctuations.First,based on the deduced DRU's frequency transfer characteristic,a fine-designed ripple carrying frequency information is superimposed on the HVDC link,transferring the onshore frequency to offshore wind turbines(WTs)via the DC ripple and coupled AC harmonic without communication.Second,multiple power sources are utilized for frequency support,including HVDC capacitance and grid-forming WTs combined with energy storage systems,and appropriate sources are activated in the order specified by the designed thresholds.Finally,the effectiveness of the proposed frequency support strategy is verified by simulations in PSCAD/EMTDC.
基金supported by the Research Project of China Southern Power Grid Co.,Ltd.(No.030400KK52220008(GDKJXM20220327))。
文摘This study analyzes the stability and reactive characteristics of the hybrid offshore wind farm that includes gridforming(GFM)and grid-following(GFL)wind turbines(WTs)integrated with a diode rectifier unit(DRU)based high-voltage direct current(HVDC)system.The determination method for the proportion of GFM WTs is proposed while considering system stability and optimal offshore reactive power constraints.First,the small-signal stability is studied based on the developed linear model,and crucial factors that affect the stability are captured by eigenvalue analysis.The reactive power-frequency compensation control of GFM WTs is then proposed to improve the reactive power and frequency dynamics.Second,the relationship between offshore reactive power imbalance and the effectiveness of GFM capability is analyzed.Offshore reactive power optimization methods are next proposed to diminish offshore reactive load.These methods include the optimal design for the reactive capacity of the AC filter and the reactive power compensation control of GFL WTs.Third,in terms of stability and optimal offshore reactive power constraints,the principle and calculation method for determining the proportion of GFM WTs are proposed,and the critical proportion of GFM WTs is determined over the full active power range.Finally,case studies using a detailed model are conducted by timedomain simulations in PSCAD/EMTDC.The simulations verify the theoretical analysis results and the effectiveness of the proposed determination method for the proportion of GFM WTs and reactive power optimization methods.
基金supported by the Scientific Research Program Funded by Shaanxi Provincial Education Department(Program No.23JP100)the Key Natural Science Research Project of Shaanxi Energy Institute:Comprehensive Characterization Study of Lithium-Ion Batteries for New Energy Vehicles(Project No.23QNZRZ01).
文摘The accurate state of health(SOH)estimation in lithium-ion batteries represents a critical technological challenge with profound implications for electric vehicle performance and user experience.Precise SOH assessment not only enables reliable mileage prediction but also ensures operational safety.However,the complex and non-linear capacity fading process during battery cycling poses a challenge to obtaining accurate SOH.To address this issue,this study proposes an effective health factor derived from the local voltage range during the battery charging phase.First,the battery charging phase is divided evenly with reference to voltage intervals,and an importance analysis is conducted on each voltage interval.From these,the voltage interval with the strongest correlation to State of Health(SOH)is extracted as the feature interval.Then,a data-driven framework integrating variational mode decomposition(VMD)with gated recurrent unit(GRU)neural networks enables comprehensive multi-scale temporal feature analysis for enhanced SOH estimation.The methodology begins with rigorous feature engineering to identify and extract optimal health indicators demonstrating superior correlation.Subsequently,the VMD algorithm performs sophisticated signal processing to decompose both the measured capacity and derived health indicators into their constituent intrinsic mode functions and residual components.Finally,a GRU-based neural network is implemented to establish a robust SOH estimation model.Experimental validation using cycling data from different datasets shows that the root mean square error of the estimation results is consistently below 3%,demonstrating the good accuracy and generalisation of the proposed method,using only local data from the charging phase.
基金supported by the National Natural Science Foundation of China,No.81373578(to YHW),81573965(to YHW)the Natural Science Foundation of Hunan Province of China,No.2017JJ3241(to JL)the Education Department Scientific Research Foundation of Hunan Province of China,No.17C1229(to JL)
文摘Previous studies have shown that models of depression exhibit structural and functional changes to the neurovascular unit. Thus, we hypothesized that diabetes-related depression might be associated with damage to the hippocampal neurovascular unit. To test this hypothesis, neurons, astrocytes and endothelial cells were isolated from the brain tissues of rat embryos and newborn rats. Hippocampal neurovascular unit co-cultures were produced using the Transwell chamber co-culture system. A model of diabetes-related depression was generated by adding 150 mM glucose and 200 μM corticosterone to the culture system and compared with the neuron + astrocyte and astrocyte + endothelial cell co-culture systems. Western blot assay was used to measure levels of structural proteins in the hippocampal neurovascular unit co-culture system. Levels of basic fibroblast growth factor, angiogenic factor 1, glial cell line–derived neurotrophic factor, transforming growth factor β1, leukemia inhibitory factor and 5-hydroxytryptamine in the hippocampal neurovascular unit co-culture system were measured by enzyme-linked immunosorbent assay. Flow cytometry and terminal deoxynucleotidyl transferase(TdT)-mediated dUTP nick end labeling staining was used to assess neuronal apoptosis in the hippocampal neurovascular unit. The neurovascular unit triple cell co-culture system had better barrier function and higher levels of structural and secretory proteins than the double cell co-culture systems. In comparison, in the model of diabetes-related depression, the neurovascular unit was damaged with decreased barrier function, poor structural integrity and impaired secretory function. Moreover, neuronal apoptosis was markedly increased, and 5-hydroxytryptamine levels were reduced. These results suggest that diabetes-related depression is associated with structural and functional damage to the neurovascular unit. Our findings provide a foundation for further studies on the pathogenesis of diabetes-related depression.
基金supported by the National Natural Science Foundation of China,No.30973782,81373526the Natural Science Foundation of Beijing,No.7102014,7122018the Beijing Municipal Higher Learning Institution Talent Teaching Plan"Young and Middle-aged Talented People Training"Project,No.PXM2011014226
文摘Houshiheisan is composed of wind-dispelling （chrysanthemun fower, divaricate saposhnikovia root, Manchurian wild ginger, cassia twig, Szechwan lovage rhizome, and platycodon root） and deficiency-nourishing （ginseng, Chinese angelica, large-head atractylodes rhizome, Indian bread, and zingiber） drugs. In this study, we assumed these drugs have protective effects against cerebral ischemia, on neurovascular units. Houshiheisan was intragastrically administered in a rat model of focal cerebral ischemia. Hematoxylin-eosin staining, transmission electron microscopy, immu- nofluorescence staining, and western blot assays showed that Houshiheisan reduced pathological injury to the ischemic penumbra, protected neurovascular units, visibly up-regtflated neuronal nuclear antigen expression, and down-regulated amyloid precursor protein and amyloid-[3 42 expression. Wind-dispelling and deficiency-nourishing drugs maintained NeuN expression to varying degrees, but did not affect amyloid precursor protein or amyloid-~ 42 expression in the ischemic penumbra. Our results suggest that the compound prescription Houshiheisan effectively suppresses abnormal amyloid precursor protein accumulation, reduces amyloid substance depo- sition, maintains stabilization of the internal environment of neurovascular units, and minimizes injury to neurovascular units in the ischemic penumbra.
