It is studied how the aluminum foil chatter mark is produced and controlled The stableness of hydraulic AGC system,fluid vibration of capsule system,and electromechanical coupling of AC/AC VVVF system and de coupli...It is studied how the aluminum foil chatter mark is produced and controlled The stableness of hydraulic AGC system,fluid vibration of capsule system,and electromechanical coupling of AC/AC VVVF system and de coupling are also studied It is shown that rolling mill design should go to system dynamic design from traditional design The framed drawing of system dynamic design program is presented.展开更多
In this paper,a series of major policy decisions used to improve the power grid reliability,reduce the risk and losses of major power outages,and realize the modernization of 21st century power grid are discussed. The...In this paper,a series of major policy decisions used to improve the power grid reliability,reduce the risk and losses of major power outages,and realize the modernization of 21st century power grid are discussed. These decisions were adopted by American government and would also be helpful for the strategic development of Chinese power grid. It is proposed that China should take precaution,carry out security research on the overall dynamic behaviour characteristics of the UHV grid using the complexity theory,and finally provide safeguard for the Chinese UHV grid. It is also pointed out that,due to the lack of matured approaches to controll a cascading failure,the primary duty of a system operator is to work as a "watchdog" for the grid operation security,eliminate the cumulative effect and reduce the risk and losses of major cascading outages with the help of EMS and WAMS.展开更多
With the rapid development of artificial intelligence(AI),it is foreseeable that the accuracy and efficiency of dynamic analysis for future power system will be greatly improved by the integration of dynamic simulator...With the rapid development of artificial intelligence(AI),it is foreseeable that the accuracy and efficiency of dynamic analysis for future power system will be greatly improved by the integration of dynamic simulators and AI.To explore the interaction mechanism of power system dynamic simulations and AI,a general design for AI-oriented power system dynamic simulators is proposed,which consists of a high-performance simulator with neural network supportability and flexible external and internal application programming interfaces(APIs).With the support of APIs,simulation-assisted AI and AIassisted simulation form a comprehensive interaction mechanism between power system dynamic simulations and AI.A prototype of this design is implemented and made public based on a highly efficient electromechanical simulator.Tests of this prototype are carried out in four scenarios including sample generation,AI-based stability prediction,data-driven dynamic component modeling,and AI-aided stability control,which prove the validity,flexibility,and efficiency of the design and implementation for AI-oriented power system dynamic simulators.展开更多
Lake eutrophication caused by excess phosphorus (P) loading from point sources (PS) and nonpoint sources (NPS) is a persistent and serious ecological problem in China. A phosphorus budget, based on material flow...Lake eutrophication caused by excess phosphorus (P) loading from point sources (PS) and nonpoint sources (NPS) is a persistent and serious ecological problem in China. A phosphorus budget, based on material flow analysis(MFA) and system dynamic (SD), is proposed and applied for the agriculture-dominated Qionghai Lake watershed located in southwestern China. The MFA-SD approach will not only cover the transporting process of P in the lake-watershed ecosystems, but also can deal with the changes of P budget due to the dynamics of watershed. P inflows include the fertilizer for agricultural croplands, soil losses, domestic sewage discharges, and the atmospheric disposition such as precipitation and dust sinking. Outflows are consisted of hydrologic export, water resources development, fishery and aquatic plants harvesting. The internal P recycling processes are also considered in this paper. From 1988 to 2015, the total P inflows for Lake Qionghai are in a rapid increase from 35.65 to 78.73 t/a, which results in the rising of P concentration in the lake. Among the total P load 2015, agricultural loss and domestic sewage account for 70.60% and 17.27% respectively, directly related to the rapid social-economic development and the swift urbanization. Future management programs designed to reduce P inputs must be put into practices in the coming years to ensure the ecosystem health in the watershed.展开更多
The current healthcare system in Hong Kong is experiencing pressure due to constrained resources,with dramatic increases in inpatient services queue lengths,dissatisfaction with the working environment,unacceptable wo...The current healthcare system in Hong Kong is experiencing pressure due to constrained resources,with dramatic increases in inpatient services queue lengths,dissatisfaction with the working environment,unacceptable workforce arrangements and high turnover rate of hospital staff.To maintain the robustness of the healthcare system and a sustainable inpatients flow,the Food and Health Bureau launched a public-private partnership programme to utilise the resources of the public and private hospitals.This research investigates the potential for extension of the programme and further enhancing the sustainability of the long-term inpatient services under a mixed public-private healthcare policy via system dynamic modelling.The findings show that an increase of human resources in public hospitals does not substantially improve inpatient flow rate performance.Further,the results from the system dynamic approach provide insights into the expansion of the service areas of the programme and suggest increasing the number of referrals to private hospitals.展开更多
Innovation and knowledge diffusion in megaprojects is one of the most complicated issues in project management.Compared with conventional projects,megaprojects typically entail large-scale investments,long constructio...Innovation and knowledge diffusion in megaprojects is one of the most complicated issues in project management.Compared with conventional projects,megaprojects typically entail large-scale investments,long construction periods,and conflicting stakeholder interests,which result in a distinctive pattern of innovation diffusion.However,traditional investigation of innovation diffusion relies on subjective feedback from experts and frequently neglects inter-organizational knowledge creation,which frequently emerges in megaprojects.Therefore,this study adopted project network theory and modeled innovation diffusion in megaprojects as intra-and interorganizational learning processes.In addition,system dynamics and flizzy systems were combined to interpret experts9 subject options as quantitative coefficients of the project network model.This integrated model will assist in developing an insightful understanding of the mechanisms of innovation diffusion in megaprojects.Three typical network structures,namely,a traditional megaproject procurement organization(TMO),the environ megaproject organization(EMO),and an integrated megaproject organization(IMO),were examined under six management scenarios to verify the proposed analytic paradigm.Assessment of project network productivity suggested that the projectivity of the TMO was insensitive to technical and administrative innovations,the EMO could achieve substantial improvement from technical innovations,and the 1MO trended incompatibly with administrative innovations.Thus,industry practitioners and project managers can design and reform agile project coordination by using the proposed quantitative model to encourage innovation adoption and reduce productivity loss at the start of newly established collaborations.展开更多
A method of enhancing power system stability for a single machine to infinite bus power system is presented. The technique used compromises the effectiveness of Proportional-Integral-Derivative controller (PID). In ...A method of enhancing power system stability for a single machine to infinite bus power system is presented. The technique used compromises the effectiveness of Proportional-Integral-Derivative controller (PID). In order to satisfy the damping characteristics for the proposed power system over a wide range of operating interval, rotational speed, torque angle and terminal voltage signals of the synchronous machine are utilized as control signals of the system. It is well known that these variables have significant effects on damping the generators shaft mechanical oscillations, it'll be so easy to validate the most suitable controller as seen from the simulation results.展开更多
The proposed maintenance strategy uses component grades and survival signature to describe and update system structure. A system dynamic stress-strength reliability(SSR) model was established to describe component fai...The proposed maintenance strategy uses component grades and survival signature to describe and update system structure. A system dynamic stress-strength reliability(SSR) model was established to describe component failure processes because of internal degradation and external shock. Besides, a corrective maintenance rule and two-level preventive maintenance rule made up the proposed maintenance strategy. The former combined sequentially minimal repair and corrective replacement(SMRCR) based on system structure updating. The latter considered group importance measure based on the system dynamic SSR and preventive maintenance cost. Further, a cost model was developed by the proposed strategy, and the optimal decision variables were found by genetic algorithm. Finally, using a case system to illustrate the above strategy improved system and reduced maintenance costs.展开更多
A new typed hydraulic system of electro hydraulic hammer is researched and developed By means of power bond graphs the modeling and simulation to the dynamic characteristics of the new hydraulic system are performed...A new typed hydraulic system of electro hydraulic hammer is researched and developed By means of power bond graphs the modeling and simulation to the dynamic characteristics of the new hydraulic system are performed The experimental research which is emphasized on the blowing stroke is also performed It is proved from the result of simulation and experiment that this new hydraulic system possesses such advantages as simplification of structure,flexibleness of operation and reliability of working Especially it possesses better dynamic characteristics展开更多
Water is a key restricting factor of the economic development and eco-environmental protection in arid inland river basins of Northwest China. Although water supplies are short, the water utilization structure and the...Water is a key restricting factor of the economic development and eco-environmental protection in arid inland river basins of Northwest China. Although water supplies are short, the water utilization structure and the corresponding industrial structure are unbalanced. We constructed a System Dynamic Model for mutual optimization based on the mechanism of their interaction. This model is applied to the Heihe River Basin where the share of limited water resources among ecosystem, production and human living is optimized. Results show that, by mutual optimization, the water utilization structure and the industrial structures fit in with each other. And the relationships between the upper, middle and lower reaches of the Heihe River Basin can be harmonized. Mutual benefits of ecology, society and economy can be reached, and a sustainable ecology-production-living system can be obtained. This study gives a new insight and method for the sustainable utilization of water resources in arid inland river basins.展开更多
Suppression of the dynamic oscillations of tie-line power exchanges and frequency in the affected interconnected power systems due to loading-condition changes has been assigned as a prominent duty of automatic genera...Suppression of the dynamic oscillations of tie-line power exchanges and frequency in the affected interconnected power systems due to loading-condition changes has been assigned as a prominent duty of automatic generation control(AGC). To alleviate the system oscillation resulting from such load changes, implementation of flexible AC transmission systems(FACTSs) can be considered as one of the practical and effective solutions. In this paper, a thyristor-controlled series compensator(TCSC), which is one series type of the FACTS family, is used to augment the overall dynamic performance of a multi-area multi-source interconnected power system. To this end, we have used a hierarchical adaptive neuro-fuzzy inference system controller-TCSC(HANFISC-TCSC) to abate the two important issues in multi-area interconnected power systems, i.e., low-frequency oscillations and tie-line power exchange deviations. For this purpose, a multi-objective optimization technique is inevitable. Multi-objective particle swarm optimization(MOPSO) has been chosen for this optimization problem, owing to its high performance in untangling non-linear objectives. The efficiency of the suggested HANFISC-TCSC has been precisely evaluated and compared with that of the conventional MOPSO-TCSC in two different multi-area interconnected power systems, i.e., two-area hydro-thermal-diesel and three-area hydro-thermal power systems. The simulation results obtained from both power systems have transparently certified the high performance of HANFISC-TCSC compared to the conventional MOPSO-TCSC.展开更多
Quickly getting back the synchronism of a disturbed interconnected multi-area power system due to variations in loading condition is recognized as prominent issue related to automatic generation control(AGC).In this r...Quickly getting back the synchronism of a disturbed interconnected multi-area power system due to variations in loading condition is recognized as prominent issue related to automatic generation control(AGC).In this regard,AGC system based on fuzzy logic,i.e.,so-called FLAGC can introduce an effectual performance to suppress the dynamic oscillations of tie-line power exchanges and frequency in multi-area interconnected power system.Apart from that,simultaneous coordination scheme based on particle swarm optimization(PSO)along with real coded genetic algorithm(RCGA)is suggested to coordinate FLAGCs of the all areas.To clarify the high efficiency of aforementioned strategy,two different interconnected multi-area power systems,i.e.,three-area hydro-thermal power system and five-area thermal power system have been taken into account for relevant studies.The potency of this strategy has been thoroughly dealt with by considering the step load perturbation(SLP)in both the under study power systems.To sum up,the simulation results have plainly revealed dynamic performance of FLAGC as compared with conventional AGC(CAGC)in each power system in order to damp out the power system oscillations.展开更多
With the widespread of new energy vehicles, charging piles have alsobeen continuously installed and constructed. In order to make the number of pilesmeet the needs of the development of new energy vehicles, this study...With the widespread of new energy vehicles, charging piles have alsobeen continuously installed and constructed. In order to make the number of pilesmeet the needs of the development of new energy vehicles, this study aims toapply the method of system dynamics and combined with the grey prediction theory to determine the parameters as well as to simulate and analyze the ratio ofvehicles to chargers. Through scenario analysis, it is predicted that by 2030, thisratio will gradually decrease from 1.79 to 1. In order to achieve this ratio as 1:1, itis necessary to speed up the construction of public charging station or privatecharging station. Due to global warming, the attitudes of countries towards fuelvehicles have become increasingly tough. There is huge uncertainty in the growthrate of electric vehicles. Therefore, it is recommended that the construction ofcharging station be deployed in advance to avoid hindering the development ofelectric vehicles in the future.展开更多
In this work,an adaptive sampling control strategy for distributed predictive control is proposed.According to the proposed method,the sampling rate of each subsystem of the accused object is determined based on the p...In this work,an adaptive sampling control strategy for distributed predictive control is proposed.According to the proposed method,the sampling rate of each subsystem of the accused object is determined based on the periodic detection of its dynamic behavior and calculations made using a correlation function.Then,the optimal sampling interval within the period is obtained and sent to the corresponding sub-prediction controller,and the sampling interval of the controller is changed accordingly before the next sampling period begins.In the next control period,the adaptive sampling mechanism recalculates the sampling rate of each subsystem’s measurable output variable according to both the abovementioned method and the change in the dynamic behavior of the entire system,and this process is repeated.Such an adaptive sampling interval selection based on an autocorrelation function that measures dynamic behavior can dynamically optimize the selection of sampling rate according to the real-time change in the dynamic behavior of the controlled object.It can also accurately capture dynamic changes,meaning that each sub-prediction controller can more accurately calculate the optimal control quantity at the next moment,significantly improving the performance of distributed model predictive control(DMPC).A comparison demonstrates that the proposed adaptive sampling DMPC algorithm has better tracking performance than the traditional DMPC algorithm.展开更多
A revised concept for urban water metabolism (UWM) is presented in this study to address the inadequacies in current research on UWM and the problems associated with the traditional urban water metabolic process. Fe...A revised concept for urban water metabolism (UWM) is presented in this study to address the inadequacies in current research on UWM and the problems associated with the traditional urban water metabolic process. Feedback loops can be analyzed to increase the water environmental carrying capacity (WECC) of the new urban water metabolism system (UWMS) over that of a traditional UWMS. An analysis of the feedback loops of an UWMS was used to construct a system dynamics (SD) model for the system under a WECC restriction. Water metabolic processes were simulated for different scenarios using the Tongzhou District in Beijing as an example. The results for the newly developed UWM case showed that a water environment of Tongzhou District could support a population of 1.1926 × 106, an irrigation area of 375.521 km2, a livestock of 0.7732 × 106, and an industrial value added of ¥193.14 × 109 (i.e. about US$28.285 × 109) in 2020. A sensitivity analysis showed that the WECC could be improved to some extent by constructing new sewage treatment facilities or by expanding the current sewage treatment facilities, using reclaimed water and improving the water circulation system.展开更多
Effective thermal control systems are essential for reliable operation of spacecraft.A dual-driven intelligent combination control strategy is proposed to improve the temperate control and heat flux tracking effects.B...Effective thermal control systems are essential for reliable operation of spacecraft.A dual-driven intelligent combination control strategy is proposed to improve the temperate control and heat flux tracking effects.Both temperature regulation and heat flux tracking errors are employed to generate the final control action;their contributions are adaptively adjusted by a fuzzy fusing policy of control actions.To evaluate the control effects,describe a four-nodal mathematical model for analyzing the dynamic characteristics of the controlled heat pipe space cooling system(HP-SCS) consisting of an aluminum-ammonia heat pipe and a variable-emittance micro-electromechanical-system(MEMS) radiator.This dynamical model calculates the mass flow-rate and condensing pressure of the heat pipe working fluid directly from the systemic nodal temperatures,therefore,it is more suitable for control engineering applications.The closed-loop transient performances of four different control schemes have been numerically investigated.The results conclude that the proposed intelligent combination control scheme not only improves the thermal control effects but also benefits the safe operation of HP-SCS.展开更多
The Brazilian transmission system is facing challenging problems with the distance between its generation areas and consumer centers that will be partly solved by the use of HVDC point-to-point systems.In the near fut...The Brazilian transmission system is facing challenging problems with the distance between its generation areas and consumer centers that will be partly solved by the use of HVDC point-to-point systems.In the near future,the southeast subsystem will have a large amount of power injected through HVDC Systems in multiple points with relatively close electrical proximity.Therefore,the effects of a multi-infeed system are expected to influence the performance and operation of the network.Extensive studies and simulations will play an important role in determining the extension of the interactions among HVDC converters and determine if such interactions cause multiple commutation failures,thus disturbing the dynamic stability of the system.The use of CCC(Capacitor Commutated Converter)HVDC systems will also be assessed and is expected to diminish the need for a strong AC network(high short circuit level)and,therefore,mitigate multi-infeed interactions.The southeast subsystem of the Brazilian Power System currently has four LCC inverters,two of them belong to the Madeira power plant and the other two are from the Itaipu power plant.By the year 2024,four other HVDC systems will be arriving in the same region.This paper discusses the HVDC multi-infeed phenomena regarding the relevance of using synchronous machine models to represent important power plants and the application of mitigation methods regarding the 2020 network model,where six HVDC links will be present.展开更多
voltage direct current(HVDC)transmission lines are being constructed throughout the world,aided by advancements in power electronics and the potential value to transfer power between distant areas and off-shore locati...voltage direct current(HVDC)transmission lines are being constructed throughout the world,aided by advancements in power electronics and the potential value to transfer power between distant areas and off-shore locations.Multiple HVDC lines within and across large AC interconnections could bring about economic benefits such as interregional capacity exchange and transfer of low-cost,distant electric energy directly to load centers.In addition,network configuration of HVDC lines could result in additional benefits that have not been deeply studied.This paper describes the modeling process for continentallevel power system interconnections with the addition of multiple HVDC lines configured as a macrogrid.The models used for study are based on industry-accepted power-flow and dynamic system models for the North American Eastern and Western Interconnections.The model provides insight on feasibility and initial steady-state and stability tests of the HVDC macrogrid and its interactions with the existing electricity infrastructure,opening the door to analysis of the technical value of such a macrogrid.展开更多
The total number of infections(epidemic size),and the time needed for the infection to die out(epidemic duration),represent two of the main indicators for the measuring gravity of infectious disease epidemics in human...The total number of infections(epidemic size),and the time needed for the infection to die out(epidemic duration),represent two of the main indicators for the measuring gravity of infectious disease epidemics in humans.A few attempts have been made to address the problem of controlling both the epidemic size and duration simultaneously from a theoretical point of view,by primarily using the Optimal control theory.In this study,a multi-objective optimal control problem has been simulated to gauge the success of the lockdowns in India.To accomplish this objective,a system dynamics modeling was used to simulate the Susceptible–Infected–Quarantined–Removed epidemic model.A set of sensitivity experiments for different scenarios allows illustrating the model’s behavior and its value for decision-makers regarding the lockdown intensity.The simulation of the model presents various scenarios,wherein the cost–benefit analysis of lockdown was done.Notably,the lockdown success intensity was defined,post which,the findings indicate that the states of Uttar Pradesh,Kerala,Panjab,Jammu,Kashmir,Haryana,and Bihar have achieved more than 90%lockdown success intensity.Further,it was observed that these states could effectively implement lockdowns by strictly enforcing social distancing measures during the early stages of the virus spread,which in turn resulted in the high success rate of lockdowns.展开更多
基金This project is supported by the 9th Five Year Plan (No-95-528-03-02-03c).
文摘It is studied how the aluminum foil chatter mark is produced and controlled The stableness of hydraulic AGC system,fluid vibration of capsule system,and electromechanical coupling of AC/AC VVVF system and de coupling are also studied It is shown that rolling mill design should go to system dynamic design from traditional design The framed drawing of system dynamic design program is presented.
文摘In this paper,a series of major policy decisions used to improve the power grid reliability,reduce the risk and losses of major power outages,and realize the modernization of 21st century power grid are discussed. These decisions were adopted by American government and would also be helpful for the strategic development of Chinese power grid. It is proposed that China should take precaution,carry out security research on the overall dynamic behaviour characteristics of the UHV grid using the complexity theory,and finally provide safeguard for the Chinese UHV grid. It is also pointed out that,due to the lack of matured approaches to controll a cascading failure,the primary duty of a system operator is to work as a "watchdog" for the grid operation security,eliminate the cumulative effect and reduce the risk and losses of major cascading outages with the help of EMS and WAMS.
基金supported in part by the National Natural Science Foundation of China (No.51877115)in part by China Postdoctoral Science Foundation (No.2021M691724)。
文摘With the rapid development of artificial intelligence(AI),it is foreseeable that the accuracy and efficiency of dynamic analysis for future power system will be greatly improved by the integration of dynamic simulators and AI.To explore the interaction mechanism of power system dynamic simulations and AI,a general design for AI-oriented power system dynamic simulators is proposed,which consists of a high-performance simulator with neural network supportability and flexible external and internal application programming interfaces(APIs).With the support of APIs,simulation-assisted AI and AIassisted simulation form a comprehensive interaction mechanism between power system dynamic simulations and AI.A prototype of this design is implemented and made public based on a highly efficient electromechanical simulator.Tests of this prototype are carried out in four scenarios including sample generation,AI-based stability prediction,data-driven dynamic component modeling,and AI-aided stability control,which prove the validity,flexibility,and efficiency of the design and implementation for AI-oriented power system dynamic simulators.
基金The Hi-Tech Research and Development Program(863) of China(No. 2002AA601021) the National Basic Research Program(973) ofChina(No. 2005CB724205) Xichang Government, Sichuan Province
文摘Lake eutrophication caused by excess phosphorus (P) loading from point sources (PS) and nonpoint sources (NPS) is a persistent and serious ecological problem in China. A phosphorus budget, based on material flow analysis(MFA) and system dynamic (SD), is proposed and applied for the agriculture-dominated Qionghai Lake watershed located in southwestern China. The MFA-SD approach will not only cover the transporting process of P in the lake-watershed ecosystems, but also can deal with the changes of P budget due to the dynamics of watershed. P inflows include the fertilizer for agricultural croplands, soil losses, domestic sewage discharges, and the atmospheric disposition such as precipitation and dust sinking. Outflows are consisted of hydrologic export, water resources development, fishery and aquatic plants harvesting. The internal P recycling processes are also considered in this paper. From 1988 to 2015, the total P inflows for Lake Qionghai are in a rapid increase from 35.65 to 78.73 t/a, which results in the rising of P concentration in the lake. Among the total P load 2015, agricultural loss and domestic sewage account for 70.60% and 17.27% respectively, directly related to the rapid social-economic development and the swift urbanization. Future management programs designed to reduce P inputs must be put into practices in the coming years to ensure the ecosystem health in the watershed.
基金Research Committee and the Department of Industrial and Systems Engineering of the Hong Kong Polytechnic University for supporting this project(G-UA7X).
文摘The current healthcare system in Hong Kong is experiencing pressure due to constrained resources,with dramatic increases in inpatient services queue lengths,dissatisfaction with the working environment,unacceptable workforce arrangements and high turnover rate of hospital staff.To maintain the robustness of the healthcare system and a sustainable inpatients flow,the Food and Health Bureau launched a public-private partnership programme to utilise the resources of the public and private hospitals.This research investigates the potential for extension of the programme and further enhancing the sustainability of the long-term inpatient services under a mixed public-private healthcare policy via system dynamic modelling.The findings show that an increase of human resources in public hospitals does not substantially improve inpatient flow rate performance.Further,the results from the system dynamic approach provide insights into the expansion of the service areas of the programme and suggest increasing the number of referrals to private hospitals.
文摘Innovation and knowledge diffusion in megaprojects is one of the most complicated issues in project management.Compared with conventional projects,megaprojects typically entail large-scale investments,long construction periods,and conflicting stakeholder interests,which result in a distinctive pattern of innovation diffusion.However,traditional investigation of innovation diffusion relies on subjective feedback from experts and frequently neglects inter-organizational knowledge creation,which frequently emerges in megaprojects.Therefore,this study adopted project network theory and modeled innovation diffusion in megaprojects as intra-and interorganizational learning processes.In addition,system dynamics and flizzy systems were combined to interpret experts9 subject options as quantitative coefficients of the project network model.This integrated model will assist in developing an insightful understanding of the mechanisms of innovation diffusion in megaprojects.Three typical network structures,namely,a traditional megaproject procurement organization(TMO),the environ megaproject organization(EMO),and an integrated megaproject organization(IMO),were examined under six management scenarios to verify the proposed analytic paradigm.Assessment of project network productivity suggested that the projectivity of the TMO was insensitive to technical and administrative innovations,the EMO could achieve substantial improvement from technical innovations,and the 1MO trended incompatibly with administrative innovations.Thus,industry practitioners and project managers can design and reform agile project coordination by using the proposed quantitative model to encourage innovation adoption and reduce productivity loss at the start of newly established collaborations.
文摘A method of enhancing power system stability for a single machine to infinite bus power system is presented. The technique used compromises the effectiveness of Proportional-Integral-Derivative controller (PID). In order to satisfy the damping characteristics for the proposed power system over a wide range of operating interval, rotational speed, torque angle and terminal voltage signals of the synchronous machine are utilized as control signals of the system. It is well known that these variables have significant effects on damping the generators shaft mechanical oscillations, it'll be so easy to validate the most suitable controller as seen from the simulation results.
基金Sponsored by the Guangdong Young Innovative Talents Project (Grant No. 2021KQNCX130)。
文摘The proposed maintenance strategy uses component grades and survival signature to describe and update system structure. A system dynamic stress-strength reliability(SSR) model was established to describe component failure processes because of internal degradation and external shock. Besides, a corrective maintenance rule and two-level preventive maintenance rule made up the proposed maintenance strategy. The former combined sequentially minimal repair and corrective replacement(SMRCR) based on system structure updating. The latter considered group importance measure based on the system dynamic SSR and preventive maintenance cost. Further, a cost model was developed by the proposed strategy, and the optimal decision variables were found by genetic algorithm. Finally, using a case system to illustrate the above strategy improved system and reduced maintenance costs.
文摘A new typed hydraulic system of electro hydraulic hammer is researched and developed By means of power bond graphs the modeling and simulation to the dynamic characteristics of the new hydraulic system are performed The experimental research which is emphasized on the blowing stroke is also performed It is proved from the result of simulation and experiment that this new hydraulic system possesses such advantages as simplification of structure,flexibleness of operation and reliability of working Especially it possesses better dynamic characteristics
基金Key Project of National Natural Science Foundation of China, No.40335049 National Natural Science Foundation of China, No.40471059
文摘Water is a key restricting factor of the economic development and eco-environmental protection in arid inland river basins of Northwest China. Although water supplies are short, the water utilization structure and the corresponding industrial structure are unbalanced. We constructed a System Dynamic Model for mutual optimization based on the mechanism of their interaction. This model is applied to the Heihe River Basin where the share of limited water resources among ecosystem, production and human living is optimized. Results show that, by mutual optimization, the water utilization structure and the industrial structures fit in with each other. And the relationships between the upper, middle and lower reaches of the Heihe River Basin can be harmonized. Mutual benefits of ecology, society and economy can be reached, and a sustainable ecology-production-living system can be obtained. This study gives a new insight and method for the sustainable utilization of water resources in arid inland river basins.
文摘Suppression of the dynamic oscillations of tie-line power exchanges and frequency in the affected interconnected power systems due to loading-condition changes has been assigned as a prominent duty of automatic generation control(AGC). To alleviate the system oscillation resulting from such load changes, implementation of flexible AC transmission systems(FACTSs) can be considered as one of the practical and effective solutions. In this paper, a thyristor-controlled series compensator(TCSC), which is one series type of the FACTS family, is used to augment the overall dynamic performance of a multi-area multi-source interconnected power system. To this end, we have used a hierarchical adaptive neuro-fuzzy inference system controller-TCSC(HANFISC-TCSC) to abate the two important issues in multi-area interconnected power systems, i.e., low-frequency oscillations and tie-line power exchange deviations. For this purpose, a multi-objective optimization technique is inevitable. Multi-objective particle swarm optimization(MOPSO) has been chosen for this optimization problem, owing to its high performance in untangling non-linear objectives. The efficiency of the suggested HANFISC-TCSC has been precisely evaluated and compared with that of the conventional MOPSO-TCSC in two different multi-area interconnected power systems, i.e., two-area hydro-thermal-diesel and three-area hydro-thermal power systems. The simulation results obtained from both power systems have transparently certified the high performance of HANFISC-TCSC compared to the conventional MOPSO-TCSC.
文摘Quickly getting back the synchronism of a disturbed interconnected multi-area power system due to variations in loading condition is recognized as prominent issue related to automatic generation control(AGC).In this regard,AGC system based on fuzzy logic,i.e.,so-called FLAGC can introduce an effectual performance to suppress the dynamic oscillations of tie-line power exchanges and frequency in multi-area interconnected power system.Apart from that,simultaneous coordination scheme based on particle swarm optimization(PSO)along with real coded genetic algorithm(RCGA)is suggested to coordinate FLAGCs of the all areas.To clarify the high efficiency of aforementioned strategy,two different interconnected multi-area power systems,i.e.,three-area hydro-thermal power system and five-area thermal power system have been taken into account for relevant studies.The potency of this strategy has been thoroughly dealt with by considering the step load perturbation(SLP)in both the under study power systems.To sum up,the simulation results have plainly revealed dynamic performance of FLAGC as compared with conventional AGC(CAGC)in each power system in order to damp out the power system oscillations.
文摘With the widespread of new energy vehicles, charging piles have alsobeen continuously installed and constructed. In order to make the number of pilesmeet the needs of the development of new energy vehicles, this study aims toapply the method of system dynamics and combined with the grey prediction theory to determine the parameters as well as to simulate and analyze the ratio ofvehicles to chargers. Through scenario analysis, it is predicted that by 2030, thisratio will gradually decrease from 1.79 to 1. In order to achieve this ratio as 1:1, itis necessary to speed up the construction of public charging station or privatecharging station. Due to global warming, the attitudes of countries towards fuelvehicles have become increasingly tough. There is huge uncertainty in the growthrate of electric vehicles. Therefore, it is recommended that the construction ofcharging station be deployed in advance to avoid hindering the development ofelectric vehicles in the future.
基金the National Natural Science Foundation of China(61563032,61963025)The Open Foundation of the Key Laboratory of Gansu Advanced Control for Industrial Processes(2019KX01)The Project of Industrial support and guidance of Colleges and Universities in Gansu Province(2019C05).
文摘In this work,an adaptive sampling control strategy for distributed predictive control is proposed.According to the proposed method,the sampling rate of each subsystem of the accused object is determined based on the periodic detection of its dynamic behavior and calculations made using a correlation function.Then,the optimal sampling interval within the period is obtained and sent to the corresponding sub-prediction controller,and the sampling interval of the controller is changed accordingly before the next sampling period begins.In the next control period,the adaptive sampling mechanism recalculates the sampling rate of each subsystem’s measurable output variable according to both the abovementioned method and the change in the dynamic behavior of the entire system,and this process is repeated.Such an adaptive sampling interval selection based on an autocorrelation function that measures dynamic behavior can dynamically optimize the selection of sampling rate according to the real-time change in the dynamic behavior of the controlled object.It can also accurately capture dynamic changes,meaning that each sub-prediction controller can more accurately calculate the optimal control quantity at the next moment,significantly improving the performance of distributed model predictive control(DMPC).A comparison demonstrates that the proposed adaptive sampling DMPC algorithm has better tracking performance than the traditional DMPC algorithm.
文摘A revised concept for urban water metabolism (UWM) is presented in this study to address the inadequacies in current research on UWM and the problems associated with the traditional urban water metabolic process. Feedback loops can be analyzed to increase the water environmental carrying capacity (WECC) of the new urban water metabolism system (UWMS) over that of a traditional UWMS. An analysis of the feedback loops of an UWMS was used to construct a system dynamics (SD) model for the system under a WECC restriction. Water metabolic processes were simulated for different scenarios using the Tongzhou District in Beijing as an example. The results for the newly developed UWM case showed that a water environment of Tongzhou District could support a population of 1.1926 × 106, an irrigation area of 375.521 km2, a livestock of 0.7732 × 106, and an industrial value added of ¥193.14 × 109 (i.e. about US$28.285 × 109) in 2020. A sensitivity analysis showed that the WECC could be improved to some extent by constructing new sewage treatment facilities or by expanding the current sewage treatment facilities, using reclaimed water and improving the water circulation system.
基金National Natural Science Foundation of China(50506003)
文摘Effective thermal control systems are essential for reliable operation of spacecraft.A dual-driven intelligent combination control strategy is proposed to improve the temperate control and heat flux tracking effects.Both temperature regulation and heat flux tracking errors are employed to generate the final control action;their contributions are adaptively adjusted by a fuzzy fusing policy of control actions.To evaluate the control effects,describe a four-nodal mathematical model for analyzing the dynamic characteristics of the controlled heat pipe space cooling system(HP-SCS) consisting of an aluminum-ammonia heat pipe and a variable-emittance micro-electromechanical-system(MEMS) radiator.This dynamical model calculates the mass flow-rate and condensing pressure of the heat pipe working fluid directly from the systemic nodal temperatures,therefore,it is more suitable for control engineering applications.The closed-loop transient performances of four different control schemes have been numerically investigated.The results conclude that the proposed intelligent combination control scheme not only improves the thermal control effects but also benefits the safe operation of HP-SCS.
基金This research was supported by ANEEL(Brazilian Energy Regulatory Agency)and the State Grid Brazilian Holding,as well as the University of Sao Paulo.
文摘The Brazilian transmission system is facing challenging problems with the distance between its generation areas and consumer centers that will be partly solved by the use of HVDC point-to-point systems.In the near future,the southeast subsystem will have a large amount of power injected through HVDC Systems in multiple points with relatively close electrical proximity.Therefore,the effects of a multi-infeed system are expected to influence the performance and operation of the network.Extensive studies and simulations will play an important role in determining the extension of the interactions among HVDC converters and determine if such interactions cause multiple commutation failures,thus disturbing the dynamic stability of the system.The use of CCC(Capacitor Commutated Converter)HVDC systems will also be assessed and is expected to diminish the need for a strong AC network(high short circuit level)and,therefore,mitigate multi-infeed interactions.The southeast subsystem of the Brazilian Power System currently has four LCC inverters,two of them belong to the Madeira power plant and the other two are from the Itaipu power plant.By the year 2024,four other HVDC systems will be arriving in the same region.This paper discusses the HVDC multi-infeed phenomena regarding the relevance of using synchronous machine models to represent important power plants and the application of mitigation methods regarding the 2020 network model,where six HVDC links will be present.
基金This work was supported by the Pacific Northwest National Laboratory operated by Battelle for the U.S.Department of Energy under contract DE-AC05-76RL01830.
文摘voltage direct current(HVDC)transmission lines are being constructed throughout the world,aided by advancements in power electronics and the potential value to transfer power between distant areas and off-shore locations.Multiple HVDC lines within and across large AC interconnections could bring about economic benefits such as interregional capacity exchange and transfer of low-cost,distant electric energy directly to load centers.In addition,network configuration of HVDC lines could result in additional benefits that have not been deeply studied.This paper describes the modeling process for continentallevel power system interconnections with the addition of multiple HVDC lines configured as a macrogrid.The models used for study are based on industry-accepted power-flow and dynamic system models for the North American Eastern and Western Interconnections.The model provides insight on feasibility and initial steady-state and stability tests of the HVDC macrogrid and its interactions with the existing electricity infrastructure,opening the door to analysis of the technical value of such a macrogrid.
文摘The total number of infections(epidemic size),and the time needed for the infection to die out(epidemic duration),represent two of the main indicators for the measuring gravity of infectious disease epidemics in humans.A few attempts have been made to address the problem of controlling both the epidemic size and duration simultaneously from a theoretical point of view,by primarily using the Optimal control theory.In this study,a multi-objective optimal control problem has been simulated to gauge the success of the lockdowns in India.To accomplish this objective,a system dynamics modeling was used to simulate the Susceptible–Infected–Quarantined–Removed epidemic model.A set of sensitivity experiments for different scenarios allows illustrating the model’s behavior and its value for decision-makers regarding the lockdown intensity.The simulation of the model presents various scenarios,wherein the cost–benefit analysis of lockdown was done.Notably,the lockdown success intensity was defined,post which,the findings indicate that the states of Uttar Pradesh,Kerala,Panjab,Jammu,Kashmir,Haryana,and Bihar have achieved more than 90%lockdown success intensity.Further,it was observed that these states could effectively implement lockdowns by strictly enforcing social distancing measures during the early stages of the virus spread,which in turn resulted in the high success rate of lockdowns.