This study investigates the distinct impacts of eastern Pacific(EP)and central Pacific(CP)El Niño events on winter shortwave solar radiation(SSR)in southern China,revealing different spatial distributions and und...This study investigates the distinct impacts of eastern Pacific(EP)and central Pacific(CP)El Niño events on winter shortwave solar radiation(SSR)in southern China,revealing different spatial distributions and underlying mechanisms.The results show that,during the developing winter of EP El Niño,significant SSR reductions occur in southwestern China and the east coast of southern China due to a strong,zonally extended Northwest Pacific anticyclone that transports moisture from the tropical Northwest Pacific and North Indian Ocean,while the northeast of southern China experiences a weak increase in SSR.In contrast,during the developing winter of CP El Niño,SSR decreases in the east of southern China with a significant decrease in the lower basin of the Yangtze River but an increase in the west of southern China with a remarkable increase in eastern Yunnan.The pronounced east-west dipole pattern in SSR anomalies is driven by a meridionally elongated Northwest Pacific anticyclone,which enhances northward moisture transport to the east of southern China while leaving western areas drier.Further research reveals that distinct moisture anomalies during the developing winter of EP and CP events result in divergent SSR distributions across southern China,primarily through modulating the total cloud cover.These findings highlight the critical need to differentiate between El Niño types when predicting medium and long-term variability of radiation in southern China.展开更多
This paper proposes an equivalent modeling method for photovoltaic(PV)power stations via a particle swarm optimization(PSO)K-means clustering(KMC)algorithm with passive filter parameter clustering to address the compl...This paper proposes an equivalent modeling method for photovoltaic(PV)power stations via a particle swarm optimization(PSO)K-means clustering(KMC)algorithm with passive filter parameter clustering to address the complexities,simulation time cost and convergence problems of detailed PV power station models.First,the amplitude–frequency curves of different filter parameters are analyzed.Based on the results,a grouping parameter set for characterizing the external filter characteristics is established.These parameters are further defined as clustering parameters.A single PV inverter model is then established as a prerequisite foundation.The proposed equivalent method combines the global search capability of PSO with the rapid convergence of KMC,effectively overcoming the tendency of KMC to become trapped in local optima.This approach enhances both clustering accuracy and numerical stability when determining equivalence for PV inverter units.Using the proposed clustering method,both a detailed PV power station model and an equivalent model are developed and compared.Simulation and hardwarein-loop(HIL)results based on the equivalent model verify that the equivalent method accurately represents the dynamic characteristics of PVpower stations and adapts well to different operating conditions.The proposed equivalent modeling method provides an effective analysis tool for future renewable energy integration research.展开更多
Influence of the gassing materials, such as PA6, PMMA, and POM on the dielectric properties of air are investigated. In this work, the fundamental electron collision cross section data were carefully selected and vali...Influence of the gassing materials, such as PA6, PMMA, and POM on the dielectric properties of air are investigated. In this work, the fundamental electron collision cross section data were carefully selected and validated. Then the species compositions of the air–organic vapor mixtures were calculated based on the Gibbs free energy minimization. Finally, the Townsend ionization coefficient, the Townsend electron attachment coefficient and the critical reduced electric field strength were derived from the calculated electron energy distribution function by solving the Boltzmann transport equation. The calculation results indicated that H;O with large attachment cross sections has a great impact on the critical reduced electric field strength of the air–organic vapor mixtures. On the other hand, the vaporization of gassing materials can help to increase the dielectric properties of air circuit breakers to some degree.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
Inaccuracy of modeling for line commutated converter based high voltage direct current (LCC-HVDC) systems will degrade the reliability of small-signal stability analysis results. Taking a practical project as the stud...Inaccuracy of modeling for line commutated converter based high voltage direct current (LCC-HVDC) systems will degrade the reliability of small-signal stability analysis results. Taking a practical project as the study system, this paper establishes a modified dynamic model by modifying the current switching function, firing angle calculation and DC voltage calculation. Then, the accuracy of the modified model is verified by a detailed electromagnetic transient (EMT) simulation. Finally, with the modified dynamic model, the impact of the control parameters and AC system strength on the small-signal stability of the overall system is investigated by adopting the eigen-analysis. The results clearly demonstrate that the modified model shows higher accuracy than the original model.展开更多
Diode rectifier unit(DRU)-based high-voltage direct current(HVDC)transmissionsystems areeffectivein achieving the stableandeconomical operation of offshore wind-powergeneration.Considering theuncontrollable characteri...Diode rectifier unit(DRU)-based high-voltage direct current(HVDC)transmissionsystems areeffectivein achieving the stableandeconomical operation of offshore wind-powergeneration.Considering theuncontrollable characteristicsof DRUs,a grid-forming(GFM)strategy forwind-turbine converters isnecessary to support offshore AC voltageand frequency.However,the active power-synchronization control in traditional GFM converters is unsuitable for DRU-based GFM converters.Thus,the stability issue for DRU-based HVDC systems involving DRU-based GFM and grid-following(GFL)converters has not yet been addressed.To solve these issues,this study begins with the characteristics of a DRU-based HVDC system and presents a control scheme for DRU-based GFM converters for power synchronization.Subsequently,the dq-frame impedance model of the DRU-based GFM converteris proposed for the stability analysis of the entire HVDC system.Finally,a simulation platform is built to verify the model accuracy and system stability.展开更多
The doubly fed induction generator(DFIG)shows multi-time-scale and strong nonlinearity,making its stability analysis difficult.This paper conducts small perturbation stability analysis for the single-DFIG infinite-bus...The doubly fed induction generator(DFIG)shows multi-time-scale and strong nonlinearity,making its stability analysis difficult.This paper conducts small perturbation stability analysis for the single-DFIG infinite-bus system with additional inertia control(AIC).First,the full-order electromagnetic transient model is constructed based on its topology and control structure.Then,the original model is reduced by using the singular perturbation method,and the validity of the simplified sixth-order model is verified by simulation.After linearising the sixth-order model based on the root locus and frequency response diagrams,it is found that increasing the gain coefficient K_(f) of the AIC could improve the inertia response characteristics but weaken the system's small disturbance stability.Furthermore,a complex torque model is constructed,which reveals that the system's negative damping originates from the terminal voltage control loop.Moreover,as K_(f) increases,the inherent damping continuously decreases,leading to further deterioration of the negative damping.As T_(f) increases,the stability of the system initially weakens and then strengthens.This study could help understand the DFIG grid-tied system dynamics.展开更多
With the widespread application of composite insulators in transmission lines,exploring the accumulation mechanism of pollution particles on composite insulator surfaces is of importance to ensure the safe and steady ...With the widespread application of composite insulators in transmission lines,exploring the accumulation mechanism of pollution particles on composite insulator surfaces is of importance to ensure the safe and steady operation of the power system.Addressing the current theoretical shortcomings,this study categorises the accumulation process of particles on the insulator surface into three stages,namely‘spatial motion’,‘surface collision’,and‘surface motion’.The motion and rotation velocities in a multi-physics field are calculated in the spatial motion stage.In the surface collision stage,a parameter called‘neck height’is introduced to determine the optimum mechanics theory,and the normal deposition criterion is established.For the surface motion stage,the sliding displacement and rolling displacement on the surface are calculated based on the rotation speed of the particles.A dynamic pollution accumulation model of the composite insulator is estab-lished based on the normal deposition criterion and tangential displacement.Finally,numerical simulations are performed by using the finite element method.Simulation results show that the proposed model agrees with the actual insulator pollution accu-mulation,and the deposition model is still applicable for various types of composite insulators operating in different applied voltages.The deposition probability of particles increases with the increasing particle size.In the surface motion stage,particle displacement increases with particle size and wind velocity.展开更多
In order to reveal the effect of insulating nano film on the insulation strength of SF_(6) gas gap,SiO_(2) nano film was deposited on the electrode surface by the plasma-enhanced chemical vapour deposition technique.T...In order to reveal the effect of insulating nano film on the insulation strength of SF_(6) gas gap,SiO_(2) nano film was deposited on the electrode surface by the plasma-enhanced chemical vapour deposition technique.The power frequency breakdown characteristics of SF_(6) gas under Cu and Al electrodes were obtained before and after coating.The results showed that when the Cu electrode was coated,the breakdown voltage was up to at most 11.5% higher than that of an uncoated Cu electrode in the pressure range of 0.2-0.5 MPa.When the Al electrode was coated,the breakdown voltage of SF_(6) gas was lower than that of an uncoated one in the pressure range of 0.2-0.5 MPa.The breakdown voltage of SF_(6) gas under the Cu electrode was slightly lower than that under the Al electrode,but the breakdown voltages under the coated Cu electrode were significantly higher than that under the coated Al electrode.Through SEM tests,it was found that the surface roughness of the electrode decreases after coating,but particles were formed on the surface of the Al electrode.The content of metal fluoride formed on the coated Al electrode under multiple breakdowns was significantly higher than that on the coated Cu electrode.The research results could provide references for improving insulation performance of GIS equipment.展开更多
As the cornerstone for the safe operation of energy systems,short-term voltage stability(STVS)has been assessed effectively with the advance of artificial intelligence(AI).However,the black-box models of traditional A...As the cornerstone for the safe operation of energy systems,short-term voltage stability(STVS)has been assessed effectively with the advance of artificial intelligence(AI).However,the black-box models of traditional AI barely identify what the specific key factors in power systems are and how they influence STVS,thus providing limited practical information for engineers in on-site dispatch centers.Enlightened by the latest explainable artificial intelligence(XAI)techniques,this paper aims to unveil the mechanism underlying the complex STVS problem.First,the ground truth for STVS is established via qualitative analysis.Based on this,an explainability score is then devised to measure the trustworthiness of different XAI techniques,among which Local Interpretable Model-agnostic Explanations(LIME)exhibits the best performance in this study.Finally,a sequential approach is proposed to extend the local interpretation of LIME to a broader scope,which is applied to enhance STVS performance before a fault occurs in distribution system load shedding,serving as an example to demonstrate the application merits of the explored mechanism.Numerical results on a modified IEEE system demonstrate that this finding facilitates the identification of the most suitable XAI technique for STVS,while also providing an interpretable mechanism for the STVS,offering accessible guidance for stability-aware dispatch.展开更多
A time-delay-dependent wide-area damping controller synthesis approach,based on Jensen’s integral inequality and evolution algorithm,is developed to suppress the adverse effect of time delay on the supplemental contr...A time-delay-dependent wide-area damping controller synthesis approach,based on Jensen’s integral inequality and evolution algorithm,is developed to suppress the adverse effect of time delay on the supplemental control of high-voltage direct current(DC)transmission systems.Initially,the state-space model of hybrid AC/DC systems with time delay is derived and the delay-dependent criteria for the stability of the closed-loop system are provided based on Jensen’s integral inequality.Subsequently,initial solutions are randomly generated to overcome the difficulty of solving the nonlinear matrix inequality.Finally,the time-delay stability upper bound of the controller is optimized using the differential evolution algorithm.In comparison to popular time-delay stable controller design methods,such as the free-weighting-matrix approach,the proposed method based on output feedback realization requires fewer decision variables and is more suitable for large-scale hybrid AC/DC systems.Three examples are introduced to verify the effectiveness of the proposed method.展开更多
There are multiple corona bursts before leader inception when the rising rate of the applied voltage or electric field is not sufficiently high enough in long positive sparks.In existing studies,no attention has been ...There are multiple corona bursts before leader inception when the rising rate of the applied voltage or electric field is not sufficiently high enough in long positive sparks.In existing studies,no attention has been paid to whether these corona bursts occur in the same location,and they are mostly considered directly as belonging to the same discharge.However,this paper presents that in a typical rod-plate long air gap,the multiple corona bursts before leader inception are distributed in at least two different locations,and the highest probability of three discharges occurs.Also,the discharge occurs with the highest probability in the time sequence‘tip-tip-side-tip-other side’of the electrode in the first five corona bursts.For each discharge,the first corona current is a single,double exponential pulse,while the following corona currents are mostly a superposition of multiple pulses.The above findings are mainly based on experiments in a 1.4 m air gap under positive switching impulses,in which the voltage,current,and high-speed images were recorded simultaneously.Finally,based on the experimental results,this paper discusses the effects brought by ignoring the multiple discharges on key parameters of leader inception and makes some suggestions to optimise long spark experiments.展开更多
基金funded by a Project from China Southern Power Grid Company Ltd.(Nos.ZBKJXM20232481 and ZBKJXM20232482)。
文摘This study investigates the distinct impacts of eastern Pacific(EP)and central Pacific(CP)El Niño events on winter shortwave solar radiation(SSR)in southern China,revealing different spatial distributions and underlying mechanisms.The results show that,during the developing winter of EP El Niño,significant SSR reductions occur in southwestern China and the east coast of southern China due to a strong,zonally extended Northwest Pacific anticyclone that transports moisture from the tropical Northwest Pacific and North Indian Ocean,while the northeast of southern China experiences a weak increase in SSR.In contrast,during the developing winter of CP El Niño,SSR decreases in the east of southern China with a significant decrease in the lower basin of the Yangtze River but an increase in the west of southern China with a remarkable increase in eastern Yunnan.The pronounced east-west dipole pattern in SSR anomalies is driven by a meridionally elongated Northwest Pacific anticyclone,which enhances northward moisture transport to the east of southern China while leaving western areas drier.Further research reveals that distinct moisture anomalies during the developing winter of EP and CP events result in divergent SSR distributions across southern China,primarily through modulating the total cloud cover.These findings highlight the critical need to differentiate between El Niño types when predicting medium and long-term variability of radiation in southern China.
基金supported by the Research Project of China Southern Power Grid(No.056200KK52222031).
文摘This paper proposes an equivalent modeling method for photovoltaic(PV)power stations via a particle swarm optimization(PSO)K-means clustering(KMC)algorithm with passive filter parameter clustering to address the complexities,simulation time cost and convergence problems of detailed PV power station models.First,the amplitude–frequency curves of different filter parameters are analyzed.Based on the results,a grouping parameter set for characterizing the external filter characteristics is established.These parameters are further defined as clustering parameters.A single PV inverter model is then established as a prerequisite foundation.The proposed equivalent method combines the global search capability of PSO with the rapid convergence of KMC,effectively overcoming the tendency of KMC to become trapped in local optima.This approach enhances both clustering accuracy and numerical stability when determining equivalence for PV inverter units.Using the proposed clustering method,both a detailed PV power station model and an equivalent model are developed and compared.Simulation and hardwarein-loop(HIL)results based on the equivalent model verify that the equivalent method accurately represents the dynamic characteristics of PVpower stations and adapts well to different operating conditions.The proposed equivalent modeling method provides an effective analysis tool for future renewable energy integration research.
基金supported by the National Key Basic Research Program of China(973 Program)2015CB251002National Natural Science Foundation of China under Grant 51521065,51577145+1 种基金the Fundamental Research Funds for the Central UniversitiesShaanxi Province Natural Science Foundation 2013JM-7010
文摘Influence of the gassing materials, such as PA6, PMMA, and POM on the dielectric properties of air are investigated. In this work, the fundamental electron collision cross section data were carefully selected and validated. Then the species compositions of the air–organic vapor mixtures were calculated based on the Gibbs free energy minimization. Finally, the Townsend ionization coefficient, the Townsend electron attachment coefficient and the critical reduced electric field strength were derived from the calculated electron energy distribution function by solving the Boltzmann transport equation. The calculation results indicated that H;O with large attachment cross sections has a great impact on the critical reduced electric field strength of the air–organic vapor mixtures. On the other hand, the vaporization of gassing materials can help to increase the dielectric properties of air circuit breakers to some degree.
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 Natural Science Foundation of China(No.51877077).
文摘Inaccuracy of modeling for line commutated converter based high voltage direct current (LCC-HVDC) systems will degrade the reliability of small-signal stability analysis results. Taking a practical project as the study system, this paper establishes a modified dynamic model by modifying the current switching function, firing angle calculation and DC voltage calculation. Then, the accuracy of the modified model is verified by a detailed electromagnetic transient (EMT) simulation. Finally, with the modified dynamic model, the impact of the control parameters and AC system strength on the small-signal stability of the overall system is investigated by adopting the eigen-analysis. The results clearly demonstrate that the modified model shows higher accuracy than the original model.
基金Supported by State Key Laboratory of HVDC(SKLHVDC-2023-KF-09).
文摘Diode rectifier unit(DRU)-based high-voltage direct current(HVDC)transmissionsystems areeffectivein achieving the stableandeconomical operation of offshore wind-powergeneration.Considering theuncontrollable characteristicsof DRUs,a grid-forming(GFM)strategy forwind-turbine converters isnecessary to support offshore AC voltageand frequency.However,the active power-synchronization control in traditional GFM converters is unsuitable for DRU-based GFM converters.Thus,the stability issue for DRU-based HVDC systems involving DRU-based GFM and grid-following(GFL)converters has not yet been addressed.To solve these issues,this study begins with the characteristics of a DRU-based HVDC system and presents a control scheme for DRU-based GFM converters for power synchronization.Subsequently,the dq-frame impedance model of the DRU-based GFM converteris proposed for the stability analysis of the entire HVDC system.Finally,a simulation platform is built to verify the model accuracy and system stability.
基金Innovation Project of China Southern Power Grid,Grant/Award Number:YN-KJXM20222153.
文摘The doubly fed induction generator(DFIG)shows multi-time-scale and strong nonlinearity,making its stability analysis difficult.This paper conducts small perturbation stability analysis for the single-DFIG infinite-bus system with additional inertia control(AIC).First,the full-order electromagnetic transient model is constructed based on its topology and control structure.Then,the original model is reduced by using the singular perturbation method,and the validity of the simplified sixth-order model is verified by simulation.After linearising the sixth-order model based on the root locus and frequency response diagrams,it is found that increasing the gain coefficient K_(f) of the AIC could improve the inertia response characteristics but weaken the system's small disturbance stability.Furthermore,a complex torque model is constructed,which reveals that the system's negative damping originates from the terminal voltage control loop.Moreover,as K_(f) increases,the inherent damping continuously decreases,leading to further deterioration of the negative damping.As T_(f) increases,the stability of the system initially weakens and then strengthens.This study could help understand the DFIG grid-tied system dynamics.
基金National Key Research and Development Program of China,Grant/Award Number:2022YFB3206800National Nature Science Foundation of China,Grant/Award Numbers:52307158,52177015。
文摘With the widespread application of composite insulators in transmission lines,exploring the accumulation mechanism of pollution particles on composite insulator surfaces is of importance to ensure the safe and steady operation of the power system.Addressing the current theoretical shortcomings,this study categorises the accumulation process of particles on the insulator surface into three stages,namely‘spatial motion’,‘surface collision’,and‘surface motion’.The motion and rotation velocities in a multi-physics field are calculated in the spatial motion stage.In the surface collision stage,a parameter called‘neck height’is introduced to determine the optimum mechanics theory,and the normal deposition criterion is established.For the surface motion stage,the sliding displacement and rolling displacement on the surface are calculated based on the rotation speed of the particles.A dynamic pollution accumulation model of the composite insulator is estab-lished based on the normal deposition criterion and tangential displacement.Finally,numerical simulations are performed by using the finite element method.Simulation results show that the proposed model agrees with the actual insulator pollution accu-mulation,and the deposition model is still applicable for various types of composite insulators operating in different applied voltages.The deposition probability of particles increases with the increasing particle size.In the surface motion stage,particle displacement increases with particle size and wind velocity.
基金National Engineering Research Center of UHV Technology and New Electrical Equipment,Grant/Award Number:NELUHV-2021-KF-06。
文摘In order to reveal the effect of insulating nano film on the insulation strength of SF_(6) gas gap,SiO_(2) nano film was deposited on the electrode surface by the plasma-enhanced chemical vapour deposition technique.The power frequency breakdown characteristics of SF_(6) gas under Cu and Al electrodes were obtained before and after coating.The results showed that when the Cu electrode was coated,the breakdown voltage was up to at most 11.5% higher than that of an uncoated Cu electrode in the pressure range of 0.2-0.5 MPa.When the Al electrode was coated,the breakdown voltage of SF_(6) gas was lower than that of an uncoated one in the pressure range of 0.2-0.5 MPa.The breakdown voltage of SF_(6) gas under the Cu electrode was slightly lower than that under the Al electrode,but the breakdown voltages under the coated Cu electrode were significantly higher than that under the coated Al electrode.Through SEM tests,it was found that the surface roughness of the electrode decreases after coating,but particles were formed on the surface of the Al electrode.The content of metal fluoride formed on the coated Al electrode under multiple breakdowns was significantly higher than that on the coated Cu electrode.The research results could provide references for improving insulation performance of GIS equipment.
基金supported in part by the National Natural Science Foundation of China under Grant U23B6008in part by the Guangdong Basic and Applied Basic Research Foundation under Grants 2022A1515240075in part by the Italian Ministry of University and Research,Project NEST,Code PE0000021,CUP J33C22002890007.
文摘As the cornerstone for the safe operation of energy systems,short-term voltage stability(STVS)has been assessed effectively with the advance of artificial intelligence(AI).However,the black-box models of traditional AI barely identify what the specific key factors in power systems are and how they influence STVS,thus providing limited practical information for engineers in on-site dispatch centers.Enlightened by the latest explainable artificial intelligence(XAI)techniques,this paper aims to unveil the mechanism underlying the complex STVS problem.First,the ground truth for STVS is established via qualitative analysis.Based on this,an explainability score is then devised to measure the trustworthiness of different XAI techniques,among which Local Interpretable Model-agnostic Explanations(LIME)exhibits the best performance in this study.Finally,a sequential approach is proposed to extend the local interpretation of LIME to a broader scope,which is applied to enhance STVS performance before a fault occurs in distribution system load shedding,serving as an example to demonstrate the application merits of the explored mechanism.Numerical results on a modified IEEE system demonstrate that this finding facilitates the identification of the most suitable XAI technique for STVS,while also providing an interpretable mechanism for the STVS,offering accessible guidance for stability-aware dispatch.
基金supported by the National Key Research and Development Program of China(2016YFB0901001).
文摘A time-delay-dependent wide-area damping controller synthesis approach,based on Jensen’s integral inequality and evolution algorithm,is developed to suppress the adverse effect of time delay on the supplemental control of high-voltage direct current(DC)transmission systems.Initially,the state-space model of hybrid AC/DC systems with time delay is derived and the delay-dependent criteria for the stability of the closed-loop system are provided based on Jensen’s integral inequality.Subsequently,initial solutions are randomly generated to overcome the difficulty of solving the nonlinear matrix inequality.Finally,the time-delay stability upper bound of the controller is optimized using the differential evolution algorithm.In comparison to popular time-delay stable controller design methods,such as the free-weighting-matrix approach,the proposed method based on output feedback realization requires fewer decision variables and is more suitable for large-scale hybrid AC/DC systems.Three examples are introduced to verify the effectiveness of the proposed method.
基金Research Grants Council of the HKSAR,Grant/Award Numbers:15208019,15210018。
文摘There are multiple corona bursts before leader inception when the rising rate of the applied voltage or electric field is not sufficiently high enough in long positive sparks.In existing studies,no attention has been paid to whether these corona bursts occur in the same location,and they are mostly considered directly as belonging to the same discharge.However,this paper presents that in a typical rod-plate long air gap,the multiple corona bursts before leader inception are distributed in at least two different locations,and the highest probability of three discharges occurs.Also,the discharge occurs with the highest probability in the time sequence‘tip-tip-side-tip-other side’of the electrode in the first five corona bursts.For each discharge,the first corona current is a single,double exponential pulse,while the following corona currents are mostly a superposition of multiple pulses.The above findings are mainly based on experiments in a 1.4 m air gap under positive switching impulses,in which the voltage,current,and high-speed images were recorded simultaneously.Finally,based on the experimental results,this paper discusses the effects brought by ignoring the multiple discharges on key parameters of leader inception and makes some suggestions to optimise long spark experiments.
