The governmental electric utility and the private sector are joining hands to meet the target of electrifying all households by 2024.However,the aforementioned goal is challenged by households that are scattered in re...The governmental electric utility and the private sector are joining hands to meet the target of electrifying all households by 2024.However,the aforementioned goal is challenged by households that are scattered in remote areas.So far,Solar Home Systems(SHS)have mostly been applied to increase electricity access in rural areas.SHSs have continuous constraints to meet electricity demands and cannot run income-generating activities.The current research presents the feasibility study of electrifying Remera village with the smart microgrid as a case study.The renewable energy resources available in Remera are the key sources of electricity in that village.The generation capacity is estimated based on the load profile.The microgrid configurations are simulated with HOMER,and the genetic algorithm is used to analyze the optimum cost.By analyzing the impact of operation and maintenance costs,the results show that the absence of subsidies increases the levelized cost of electricity(COE)five times greater than the electricity price from the public utility.The microgrid made up of PV,diesel generator,and batteries proved to be the most viable solution and ensured continuous power supply to customers.By considering the subsidies,COE reaches 0.186$/kWh,a competitive price with electricity from public utilities in Rwanda.展开更多
Given the increasing uncertainties in power supply and load,this paper proposes the concept of power source and grid coordination uniformity planning.In this approach,the standard deviation of the transmission line lo...Given the increasing uncertainties in power supply and load,this paper proposes the concept of power source and grid coordination uniformity planning.In this approach,the standard deviation of the transmission line load rate is considered as the uniformity evaluation index for power source and grid planning.A multi-stage and multi-objective optimization model of the power source and grid expansion planning is established to minimize the comprehensive cost of the entire planning cycle.In this study,the improved particle swarm optimization algorithm and genetic algorithm are combined to solve the model,thus improving the efficiency and accuracy of the solution.The analysis of a simple IEEE Garver’s 6-node system shows that the model and solution method are effective and feasible.Moreover,they are suitable for the coordinated planning of the power source and grid under a diversified nature of power supply and load.展开更多
To analyze and control complex networks effectively, this paper puts forward a new kind of scheme, which takes control separately in each area and can achieve the network’s coordinated optimality. The proposed algori...To analyze and control complex networks effectively, this paper puts forward a new kind of scheme, which takes control separately in each area and can achieve the network’s coordinated optimality. The proposed algorithm is made up of two parts: the first part decomposes the network into several independent areas based on community structure and decouples the information flow and control power among areas; the second part selects the center nodes from each area with the help of the control centrality index. As long as the status of center nodes is kept on a satisfactory level in each area, the whole system is under effective control. Finally, the algorithm is applied to power grids, and the simulations prove its effectiveness.展开更多
A grid service composite process is made up of complex coordinative activities.Developing the appropriate model of grid service coordinative activities is an important foundation for the grid service composition.Accor...A grid service composite process is made up of complex coordinative activities.Developing the appropriate model of grid service coordinative activities is an important foundation for the grid service composition.According to the coordination theory,this paper elaborates the process of the grid service composition by using UML 2.0,and proposes an approach to modelling the grid service composition process based on the coordination theory.This approach helps not only to analyze accurately the task activities and relevant dependencies among task activities,but also to facilitate the adaptability of the grid service orchestration to further realize the connectivity,timeliness,appropriateness and expansibility of the grid service composition.展开更多
For multiple grid-connected inverters with active filter function,it makes sense to regulate every unit to output maximum active power from photovoltaic arrays,as well as eliminate the harmonic due to the non-linear l...For multiple grid-connected inverters with active filter function,it makes sense to regulate every unit to output maximum active power from photovoltaic arrays,as well as eliminate the harmonic due to the non-linear loads connected to the electric networks.Naturally,a centralized control coordination strategy was proposed for the purpose of high facility utilization,good harmonic compensation ability and unwanted overcompensation condition.Based on a vector decoupling control scheme and generalized instantaneous reactive power theory,the solution was to allocate the harmonic eliminating task for every inverter according to the instantaneous power margin of each.The grid current always keeps sinusoidal in spite of non-linear load change and output active power change for any inverter.The simulation results validate the efficacy of the proposed coordination strategy.展开更多
Computerized power management system with fast and optimal communication network overcomes all major dicrepencies of undue or inadequate load relief that were present in old conventional systems. This paper presents t...Computerized power management system with fast and optimal communication network overcomes all major dicrepencies of undue or inadequate load relief that were present in old conventional systems. This paper presents the basic perception and methodology of modern and true intelligent load management scheme in micro grids topology by employing TCP/IP protocol for fast and intelligent switching. The network understudy performs load management and power distribution intelligently in a unified network. Generated power is efficiently distributed among local loads through fast communication system of server in the form of source and clients in the form of loads through TCP/IP. The efficient use of information between server and clients enables to astutely control the load management in a power system of micro grids system. The processing time of above stated system comes out to be 10ms faster than others which ensure very less delay as compared to conventional methods. The Micro Grids system operating through TCP/IP control has been implemented in MATLAB/Simulink and results have been verified.展开更多
This paper presents, tests and compares three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types during the connected mode. The main contribution of this work is including the ...This paper presents, tests and compares three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types during the connected mode. The main contribution of this work is including the models of all the micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included in the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the connecting mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current protection relays. With using TN system, Touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited value if current limiter is included with the transformer of the main grid which connects MG. For the two others earthing systems (TT and IT), fault current is small and nearly equal to the over load current which make over current protection relay can not differentiate between fault current and overload current. All models of micro sources, earthing systems, inverters, main grid and control schemes are built using Matlab?/Simulink? environment.展开更多
Microgrids have been proposed in order to improve reliability and stability of electrical system and to ensure power quality of grid. Microgrid consists of low voltage distribution systems with distributed energy reso...Microgrids have been proposed in order to improve reliability and stability of electrical system and to ensure power quality of grid. Microgrid consists of low voltage distribution systems with distributed energy resources, such as wind turbine and photovoltaic power systems, together with storage devices. It is essential to protect a micro grid in both the grid-connected and the islanded mode of operation against all different types of faults. This paper describes micro grid protection and safety concept with central control and monitoring unit where multifunctional intelligent digital relay could be used. This central control & monitoring infrastructure is used for adaptive relay settings strategy for micro grid protection. Also operational safety design concept and fault mitigation technique is proposed to ensure confidence in protection system.展开更多
This paper presents and tests three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types when the MG transferred to the islanding mode. The main contribution of this work is incl...This paper presents and tests three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types when the MG transferred to the islanding mode. The main contribution of this work is including the models of all micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included with the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the islanding mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current pro-tection relays. With using TN earthing system, touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited values during islanding mode. For the two others earthing systems (TT and IT), fault currents are small and nearly equal to the over load currents which make over current protection relay can not differentiate between fault currents and overload currents. All models of micro sources, earthing systems, inverters and control schemes are built using Matlab?/Simulink? environment.展开更多
Optoelectronic characterisation of an individual ZnO nanowire in contact with a micro-grid template has been studied. The low-cost micro-grid template made by photolithography is used to fabricate the ohmic contact me...Optoelectronic characterisation of an individual ZnO nanowire in contact with a micro-grid template has been studied. The low-cost micro-grid template made by photolithography is used to fabricate the ohmic contact metal electrodes. The current increases linearly with the bias, indicating good ohmic contacts between the nanowire and the electrodes. The resistivity of the ZnO nanowire is calculated to be 3.8 Ω·cm. We investigate the photoresponses of an individual ZnO nanowire under different light illumination using light emitting diodes (λ= 505 nm, 460 nm, 375 nm) as excitation sources in atmosphere. When individual ZnO nanowire is exposured to different light irradiation, we find that it is extremely sensitive to UV illumination; the conductance is much larger upon UV illumination than that in the dark at room temperature. This phenomenon may be related to the surface oxygen molecule adsorbtion, which indicates their potential application to the optoelectronic switching device.展开更多
Micro-grids comprise low voltage distribution systems with distributed energy resources(DERs) and controllable loads which can operate connected to the medium voltage grid or islanded in a controlled coordinated way. ...Micro-grids comprise low voltage distribution systems with distributed energy resources(DERs) and controllable loads which can operate connected to the medium voltage grid or islanded in a controlled coordinated way. This concept aims to move from "connect and forget" philosophy towards a full integration of DERs. Micro-grids can provide numerous economic and environmental benefits for end-customers, utilities and society. However, their implementation poses great technical challenges, such as a new philosophy in design of protection systems. In this work, a micro-grid protection scheme is presented based on positive-sequence component using phasor measurement units(PMUs) and a central protection unit(CPU). The salient feature of the proposed scheme in comparison with the previous works is that it has the ability to protect both radial and looped micro-grids against different types of faults with the capability of single-phase tripping. Furthermore, since the CPU is capable of updating its pickup values(upstream and downstream equivalent positive-sequence impedances of each line) after the first change in the micro-grid configuration(such as transferring from grid-connected to islanded mode and or disconnection of a line, bus, or DER either in grid-connected mode or in islanded mode), it can protect micro-grid against subsequent faults. Finally, in order to verify the effectiveness of the suggested scheme and the CPU, several simulations have been undertaken by using DIg SILENT Power Factory and MATLAB software packages.展开更多
After implementing CGCS2000,establishing grid models for high-accuracy coordinate transformation which are mainly used to transform border lines and coordinate grids of topographic maps becomes an important issue in m...After implementing CGCS2000,establishing grid models for high-accuracy coordinate transformation which are mainly used to transform border lines and coordinate grids of topographic maps becomes an important issue in mapping applications.Consequently,a grid model for high-accuracy coordinate transformation of CGCS2000 is proposed.Specifically,we firstly analyze a minimum curvature equation of coordinate transformation,which possesses the characteristics of both the global and local smoothness,achieving better consistency with the consecutive smoothness for the coordinate transformation of map’s linear feature.Then an iterative calculation method of grid nodes and an approach for establishing regional grid models based on collocation by two-step minimization are proposed.Meanwhile,a data structure of grid model is constructed.Finally we give the optimized grid interval and transformation accuracy in China corresponding to the proposed grid model.Using 48 433 points of 2000 National Geodetic Control Network of China,we take the proposed model into practice by constructing grid models for coordinate transformation from BJS54 and XAS80 to CGCS2000,and the external positional accuracies for both models are 0.26 m and 0.03 m respectively.展开更多
Scarcity of fossil fuel resources has motivated the researchers to develop renewable energy based power projects. Instead of using a single or independent renewable energy source, it is preferable to use the combinati...Scarcity of fossil fuel resources has motivated the researchers to develop renewable energy based power projects. Instead of using a single or independent renewable energy source, it is preferable to use the combination of such energy sources in a distributed way to compensate the power fluctuations of the system and this leads to the concept of hybrid micro-grid energy. Voltage stability is an important parameter for the secure operation of the hybrid-micro grid, and IEEE 1547 Standard defines the limit of the voltage for the successful operation of the micro-grid. Although Vanadium Redox Batteries (VRBs) can help the system to stabilize the voltage when voltage sag occurs when a heavy load is suddenly connected to the system, this stabilization process takes some time. This paper discusses the application of super capacitors to the hybrid micro-grid system, as a higher energy density element, to help the system quickly recover its transient voltage.展开更多
This paper describes a micro-grid system and its monitoring system. This micro-grid system consists of generation systems, consumer electrical equipments, auxiliary equipments and the monitoring system. All the equipm...This paper describes a micro-grid system and its monitoring system. This micro-grid system consists of generation systems, consumer electrical equipments, auxiliary equipments and the monitoring system. All the equipments have 485 communication interfaces. In order to monitor and manage this micro-grid system, we built a monitoring system, which contains modular instrument system and industrial personal computer. In order to keep real time, we adopt some measures in software and hardware. We adopt LABVIEW and its program modules in software and adopt modular instrument system in hardware. Supporting by the software and hardware, the micro-grid system can be safe and stable.展开更多
This paper presents the design and implementation of an energy management system (EMS) with wavelet transform and fuzzy control for a residential micro-grid. The hybrid system in this paper consists of a wind turbin...This paper presents the design and implementation of an energy management system (EMS) with wavelet transform and fuzzy control for a residential micro-grid. The hybrid system in this paper consists of a wind turbine generator, photovoltaic (PV) panels, an electric vehicle (EV), and a super capacitor (SC), which is able to connect or disconnect to the main grid. The control strategy is responsible for compensating the difference between the generated power by the wind and solar generators and the demanded power by the loads. Wavelet transform decomposes the power difference into a smoothed component and a fast fluctuated component. The command approach used for fuzzy logic rules considers the state of charging (SOC) of EV, renewable production, and the load demand as parameters. Furthermore, the command rules are developed in order to ensure a reliable grid when taking into account the EV battery protection to decide the output power of the EV. The model of the hybrid system is developed in detail under Matlab/Simulink software environment.展开更多
The unintentional islanding of micro-grid may cause negative impacts on distribution loads and distributed generations,so it must be detected within the acceptable duration.In this paper a new islanding detection algo...The unintentional islanding of micro-grid may cause negative impacts on distribution loads and distributed generations,so it must be detected within the acceptable duration.In this paper a new islanding detection algorithm is proposed.This algorithm introduces the frequency feedback method by the reactive power compensation to derive the frequency continuous shift. Accordingly,the islanding can be detected by monitoring the frequency within 0.1 s.The simulation results prove that this algorithm has extremely small non-detection zone,and meanwhile it presents an excellent islanding detection speed as well.展开更多
We give a brief discussion of some of the contributions of Peter Lax to Com- putational Fluid Dynamics. These include the Lax-Friedrichs and Lax-Wendroff numerical schemes. We also mention his collaboration in the 198...We give a brief discussion of some of the contributions of Peter Lax to Com- putational Fluid Dynamics. These include the Lax-Friedrichs and Lax-Wendroff numerical schemes. We also mention his collaboration in the 1983 HLL Riemann solver. We de- velop two-dimensional Lax-Friedrichs and Lax-Wendroff schemes for the Lagrangian form of the Euler equations on triangular grids. We apply a composite scheme that uses a Lax- Friedrichs time step as a dissipative filter after several Lax-Wendroff time steps. Numerical results for Noh's infinite strength shock problem, the Sedov blast wave problem, and the Saltzman piston problem are presented.展开更多
A new approach based on stereo vision technology is introduced to analyzesheet metal deformation. By measuring the deformed circle grids that are printed on the sheetsurface before forming, the strain distribution of ...A new approach based on stereo vision technology is introduced to analyzesheet metal deformation. By measuring the deformed circle grids that are printed on the sheetsurface before forming, the strain distribution of the workpiece is obtained. The measurement andanalysis results can be used to verify numerical simulation results and guide production. To getgood accuracy, some new techniques are employed: camera calibration based on genetic algorithm,feature abstraction based on self-adaptive technology, image matching based on structure feature andcamera modeling pre-constrains, and parameter calculation based on curve and surface optimization.The experimental values show that the approach proposed is rational and practical, which can providebetter measurement accuracy with less time than the conventional method.展开更多
文摘The governmental electric utility and the private sector are joining hands to meet the target of electrifying all households by 2024.However,the aforementioned goal is challenged by households that are scattered in remote areas.So far,Solar Home Systems(SHS)have mostly been applied to increase electricity access in rural areas.SHSs have continuous constraints to meet electricity demands and cannot run income-generating activities.The current research presents the feasibility study of electrifying Remera village with the smart microgrid as a case study.The renewable energy resources available in Remera are the key sources of electricity in that village.The generation capacity is estimated based on the load profile.The microgrid configurations are simulated with HOMER,and the genetic algorithm is used to analyze the optimum cost.By analyzing the impact of operation and maintenance costs,the results show that the absence of subsidies increases the levelized cost of electricity(COE)five times greater than the electricity price from the public utility.The microgrid made up of PV,diesel generator,and batteries proved to be the most viable solution and ensured continuous power supply to customers.By considering the subsidies,COE reaches 0.186$/kWh,a competitive price with electricity from public utilities in Rwanda.
基金supported by Theoretical study of power system synergistic dispatch National Science Foundation of China(51477091).
文摘Given the increasing uncertainties in power supply and load,this paper proposes the concept of power source and grid coordination uniformity planning.In this approach,the standard deviation of the transmission line load rate is considered as the uniformity evaluation index for power source and grid planning.A multi-stage and multi-objective optimization model of the power source and grid expansion planning is established to minimize the comprehensive cost of the entire planning cycle.In this study,the improved particle swarm optimization algorithm and genetic algorithm are combined to solve the model,thus improving the efficiency and accuracy of the solution.The analysis of a simple IEEE Garver’s 6-node system shows that the model and solution method are effective and feasible.Moreover,they are suitable for the coordinated planning of the power source and grid under a diversified nature of power supply and load.
基金the National Science Foundation of China (No.50525721, 50595411)the National Basic Research Program of China(No.G2004CB217902)
文摘To analyze and control complex networks effectively, this paper puts forward a new kind of scheme, which takes control separately in each area and can achieve the network’s coordinated optimality. The proposed algorithm is made up of two parts: the first part decomposes the network into several independent areas based on community structure and decouples the information flow and control power among areas; the second part selects the center nodes from each area with the help of the control centrality index. As long as the status of center nodes is kept on a satisfactory level in each area, the whole system is under effective control. Finally, the algorithm is applied to power grids, and the simulations prove its effectiveness.
基金supported by the National Natural Science Foundation of China(70771109)
文摘A grid service composite process is made up of complex coordinative activities.Developing the appropriate model of grid service coordinative activities is an important foundation for the grid service composition.According to the coordination theory,this paper elaborates the process of the grid service composition by using UML 2.0,and proposes an approach to modelling the grid service composition process based on the coordination theory.This approach helps not only to analyze accurately the task activities and relevant dependencies among task activities,but also to facilitate the adaptability of the grid service orchestration to further realize the connectivity,timeliness,appropriateness and expansibility of the grid service composition.
基金Project(51107111)supported by the National Natural Science Foundation of China
文摘For multiple grid-connected inverters with active filter function,it makes sense to regulate every unit to output maximum active power from photovoltaic arrays,as well as eliminate the harmonic due to the non-linear loads connected to the electric networks.Naturally,a centralized control coordination strategy was proposed for the purpose of high facility utilization,good harmonic compensation ability and unwanted overcompensation condition.Based on a vector decoupling control scheme and generalized instantaneous reactive power theory,the solution was to allocate the harmonic eliminating task for every inverter according to the instantaneous power margin of each.The grid current always keeps sinusoidal in spite of non-linear load change and output active power change for any inverter.The simulation results validate the efficacy of the proposed coordination strategy.
文摘Computerized power management system with fast and optimal communication network overcomes all major dicrepencies of undue or inadequate load relief that were present in old conventional systems. This paper presents the basic perception and methodology of modern and true intelligent load management scheme in micro grids topology by employing TCP/IP protocol for fast and intelligent switching. The network understudy performs load management and power distribution intelligently in a unified network. Generated power is efficiently distributed among local loads through fast communication system of server in the form of source and clients in the form of loads through TCP/IP. The efficient use of information between server and clients enables to astutely control the load management in a power system of micro grids system. The processing time of above stated system comes out to be 10ms faster than others which ensure very less delay as compared to conventional methods. The Micro Grids system operating through TCP/IP control has been implemented in MATLAB/Simulink and results have been verified.
文摘This paper presents, tests and compares three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types during the connected mode. The main contribution of this work is including the models of all the micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included in the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the connecting mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current protection relays. With using TN system, Touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited value if current limiter is included with the transformer of the main grid which connects MG. For the two others earthing systems (TT and IT), fault current is small and nearly equal to the over load current which make over current protection relay can not differentiate between fault current and overload current. All models of micro sources, earthing systems, inverters, main grid and control schemes are built using Matlab?/Simulink? environment.
文摘Microgrids have been proposed in order to improve reliability and stability of electrical system and to ensure power quality of grid. Microgrid consists of low voltage distribution systems with distributed energy resources, such as wind turbine and photovoltaic power systems, together with storage devices. It is essential to protect a micro grid in both the grid-connected and the islanded mode of operation against all different types of faults. This paper describes micro grid protection and safety concept with central control and monitoring unit where multifunctional intelligent digital relay could be used. This central control & monitoring infrastructure is used for adaptive relay settings strategy for micro grid protection. Also operational safety design concept and fault mitigation technique is proposed to ensure confidence in protection system.
文摘This paper presents and tests three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types when the MG transferred to the islanding mode. The main contribution of this work is including the models of all micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included with the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the islanding mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current pro-tection relays. With using TN earthing system, touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited values during islanding mode. For the two others earthing systems (TT and IT), fault currents are small and nearly equal to the over load currents which make over current protection relay can not differentiate between fault currents and overload currents. All models of micro sources, earthing systems, inverters and control schemes are built using Matlab?/Simulink? environment.
基金supported by the National Natural Science Foundation of China (Grant Nso. 60776010,60940021 and 11074060)the Natural Science Foundation of Heilongjiang Province,China (Grant No. A2008-07)the Doctoral Start-up Fund of Harbin Normal University,China
文摘Optoelectronic characterisation of an individual ZnO nanowire in contact with a micro-grid template has been studied. The low-cost micro-grid template made by photolithography is used to fabricate the ohmic contact metal electrodes. The current increases linearly with the bias, indicating good ohmic contacts between the nanowire and the electrodes. The resistivity of the ZnO nanowire is calculated to be 3.8 Ω·cm. We investigate the photoresponses of an individual ZnO nanowire under different light illumination using light emitting diodes (λ= 505 nm, 460 nm, 375 nm) as excitation sources in atmosphere. When individual ZnO nanowire is exposured to different light irradiation, we find that it is extremely sensitive to UV illumination; the conductance is much larger upon UV illumination than that in the dark at room temperature. This phenomenon may be related to the surface oxygen molecule adsorbtion, which indicates their potential application to the optoelectronic switching device.
文摘Micro-grids comprise low voltage distribution systems with distributed energy resources(DERs) and controllable loads which can operate connected to the medium voltage grid or islanded in a controlled coordinated way. This concept aims to move from "connect and forget" philosophy towards a full integration of DERs. Micro-grids can provide numerous economic and environmental benefits for end-customers, utilities and society. However, their implementation poses great technical challenges, such as a new philosophy in design of protection systems. In this work, a micro-grid protection scheme is presented based on positive-sequence component using phasor measurement units(PMUs) and a central protection unit(CPU). The salient feature of the proposed scheme in comparison with the previous works is that it has the ability to protect both radial and looped micro-grids against different types of faults with the capability of single-phase tripping. Furthermore, since the CPU is capable of updating its pickup values(upstream and downstream equivalent positive-sequence impedances of each line) after the first change in the micro-grid configuration(such as transferring from grid-connected to islanded mode and or disconnection of a line, bus, or DER either in grid-connected mode or in islanded mode), it can protect micro-grid against subsequent faults. Finally, in order to verify the effectiveness of the suggested scheme and the CPU, several simulations have been undertaken by using DIg SILENT Power Factory and MATLAB software packages.
基金The National Natural Science Foundation Program(41674019)The National Plan on Key Basic Research and Development of China(2016YFB0501701).
文摘After implementing CGCS2000,establishing grid models for high-accuracy coordinate transformation which are mainly used to transform border lines and coordinate grids of topographic maps becomes an important issue in mapping applications.Consequently,a grid model for high-accuracy coordinate transformation of CGCS2000 is proposed.Specifically,we firstly analyze a minimum curvature equation of coordinate transformation,which possesses the characteristics of both the global and local smoothness,achieving better consistency with the consecutive smoothness for the coordinate transformation of map’s linear feature.Then an iterative calculation method of grid nodes and an approach for establishing regional grid models based on collocation by two-step minimization are proposed.Meanwhile,a data structure of grid model is constructed.Finally we give the optimized grid interval and transformation accuracy in China corresponding to the proposed grid model.Using 48 433 points of 2000 National Geodetic Control Network of China,we take the proposed model into practice by constructing grid models for coordinate transformation from BJS54 and XAS80 to CGCS2000,and the external positional accuracies for both models are 0.26 m and 0.03 m respectively.
文摘Scarcity of fossil fuel resources has motivated the researchers to develop renewable energy based power projects. Instead of using a single or independent renewable energy source, it is preferable to use the combination of such energy sources in a distributed way to compensate the power fluctuations of the system and this leads to the concept of hybrid micro-grid energy. Voltage stability is an important parameter for the secure operation of the hybrid-micro grid, and IEEE 1547 Standard defines the limit of the voltage for the successful operation of the micro-grid. Although Vanadium Redox Batteries (VRBs) can help the system to stabilize the voltage when voltage sag occurs when a heavy load is suddenly connected to the system, this stabilization process takes some time. This paper discusses the application of super capacitors to the hybrid micro-grid system, as a higher energy density element, to help the system quickly recover its transient voltage.
文摘This paper describes a micro-grid system and its monitoring system. This micro-grid system consists of generation systems, consumer electrical equipments, auxiliary equipments and the monitoring system. All the equipments have 485 communication interfaces. In order to monitor and manage this micro-grid system, we built a monitoring system, which contains modular instrument system and industrial personal computer. In order to keep real time, we adopt some measures in software and hardware. We adopt LABVIEW and its program modules in software and adopt modular instrument system in hardware. Supporting by the software and hardware, the micro-grid system can be safe and stable.
基金supported by the National Science Foundation of China under Grant No.51205046
文摘This paper presents the design and implementation of an energy management system (EMS) with wavelet transform and fuzzy control for a residential micro-grid. The hybrid system in this paper consists of a wind turbine generator, photovoltaic (PV) panels, an electric vehicle (EV), and a super capacitor (SC), which is able to connect or disconnect to the main grid. The control strategy is responsible for compensating the difference between the generated power by the wind and solar generators and the demanded power by the loads. Wavelet transform decomposes the power difference into a smoothed component and a fast fluctuated component. The command approach used for fuzzy logic rules considers the state of charging (SOC) of EV, renewable production, and the load demand as parameters. Furthermore, the command rules are developed in order to ensure a reliable grid when taking into account the EV battery protection to decide the output power of the EV. The model of the hybrid system is developed in detail under Matlab/Simulink software environment.
基金National High-Tech R&D Program of China(No.2007AA05Z241).
文摘The unintentional islanding of micro-grid may cause negative impacts on distribution loads and distributed generations,so it must be detected within the acceptable duration.In this paper a new islanding detection algorithm is proposed.This algorithm introduces the frequency feedback method by the reactive power compensation to derive the frequency continuous shift. Accordingly,the islanding can be detected by monitoring the frequency within 0.1 s.The simulation results prove that this algorithm has extremely small non-detection zone,and meanwhile it presents an excellent islanding detection speed as well.
基金performed under the auspices of the National Nuclear Security Administration of the US Department of Energy at Los Alamos National Laboratory under Contract No.DE-AC52-06NA25396supported in part by the Czech Science Foundation GrantP205/10/0814the Czech Ministry of Education grants MSM 6840770022 and LC528
文摘We give a brief discussion of some of the contributions of Peter Lax to Com- putational Fluid Dynamics. These include the Lax-Friedrichs and Lax-Wendroff numerical schemes. We also mention his collaboration in the 1983 HLL Riemann solver. We de- velop two-dimensional Lax-Friedrichs and Lax-Wendroff schemes for the Lagrangian form of the Euler equations on triangular grids. We apply a composite scheme that uses a Lax- Friedrichs time step as a dissipative filter after several Lax-Wendroff time steps. Numerical results for Noh's infinite strength shock problem, the Sedov blast wave problem, and the Saltzman piston problem are presented.
文摘A new approach based on stereo vision technology is introduced to analyzesheet metal deformation. By measuring the deformed circle grids that are printed on the sheetsurface before forming, the strain distribution of the workpiece is obtained. The measurement andanalysis results can be used to verify numerical simulation results and guide production. To getgood accuracy, some new techniques are employed: camera calibration based on genetic algorithm,feature abstraction based on self-adaptive technology, image matching based on structure feature andcamera modeling pre-constrains, and parameter calculation based on curve and surface optimization.The experimental values show that the approach proposed is rational and practical, which can providebetter measurement accuracy with less time than the conventional method.