This paper refers to an integrated mCCHP （micro-combined cooling heat and power） systems dedicated for isolated residents with energetic independence. The only energy sources are wood pellet and solar energy. The pr...This paper refers to an integrated mCCHP （micro-combined cooling heat and power） systems dedicated for isolated residents with energetic independence. The only energy sources are wood pellet and solar energy. The proposed trigeneration system is based on mCHP （micro-combined heat and power） unit with Stirling engine, photovoltaic panels, thermal solar collector and pellet boiler. The proposed mCCHP system utilizes the exceeding amount of heat in the summer for producing the necessary cooling. A residential building with known energy consumption is determined load curves that must be covered by mCCHP system. The paper analyzes four structures of trigeneration systems with thermal activation chiller and two structures of trigeneration systems with mechanical compression chiller. Performance indicators are determined based on energy balance equations for each variant. It compares the performances and establishes the best option.展开更多
Background Droughts likely lead to the decrease of vegetation coverage and plant productivity.Due to climate change,more extreme climatic events,including soil droughts and extreme temperatures,may occur both independ...Background Droughts likely lead to the decrease of vegetation coverage and plant productivity.Due to climate change,more extreme climatic events,including soil droughts and extreme temperatures,may occur both independently and simultaneously.Therefore,it is important to understand the thresholds of soil drought in order to avoid various undesired transitions of alpine grassland.Methods Soil droughts were identified based on the change of soil moisture,and vegetation coverage decline events were identified by the abnormal decrease of normalized difference vegetation index(NDVI).Three thresholds based on two curves of vegetation responses to soil drought illustrated the tipping points that reflected the rapid loss of ecosystem resistance(T_(p1)),the complete loss of ecosystem resistance(T_(p2))and the amplified magnitude of NDVI decrease(T_(m)).The influences of legacy effects and extreme temperatures were also considered.Results Alpine grasslands in northeastern Qinghai-Tibet Plateau had mean T_(p1),T_(p2)and T_(m)of 1.25,1.98 and 1.93,respectively,indicating low resistance and high vulnerability.T_(p1)was low for the most study area,and T_(p2)and Tmva ried with elevation and vegetation types.Besides the low occurrence of soil droughts coupled with high temperatures,the extremely low temperatures decreased 36%T_(p1),nearly all of T_(p2)and 30%T_(m).Different grassland types showed varying responses to soil droughts,with alpine sparse vegetation having the lowest resistance and alpine wetland having the highest.However,the responses according to soil types did not show obvious differences.Conclusions Alpine grasslands in northeastern Qinghai-Tibet Plateau were sensitive to soil droughts,and extremely low temperatures intensified the decrease of ecosystem resistance to soil drought.The identification of soil drought thresholds advances the understanding of how alpine grassland responds to soil droughts,and helps the restoration of alpine grasslands when faced with soil droughts and benefits climate adaptation.展开更多
Intensive studies have been carried out on generations of waverider geometry and hypersonic inlet geometry. However, integration efforts of waverider and related air-intake system are restricted majorly around the X43...Intensive studies have been carried out on generations of waverider geometry and hypersonic inlet geometry. However, integration efforts of waverider and related air-intake system are restricted majorly around the X43A-like or conical flow field induced configuration, which adopts mainly the two-dimensional air-breathing technology and limits the judicious visions of developing new aerodynamic profiles for hypersonic designers. A novel design approach for integrating the inward turning inlet with the traditional parameterized waverider is proposed. The proposed method is an alternative means to produce a compatible configuration by linking the off-the-shelf results on both traditional waverider techniques and inward turning inlet techniques. A series of geometry generations and optimization solutions is proposed to enhance the lift-to-drag ratio. A quantitative but efficient aerodynamic performance evaluation approach （the hypersonic flow panel method） with lower computational cost is employed to play the role of objective function for opti- mization purpose. The produced geometry compatibility with a computational fluid dynamics （CFD） solver is also verified for detailed flow field investigation. Optimization results and other numerical validations are obtained for the feasibility demonstration of the proposed method.展开更多
A global fast terminal sliding mode(GFTSM)-based model predictive torque control(MPTC)strategy is developed for permanent magnet synchronous motor(PMSM)drive system with only one phase current sensor.Generally two pha...A global fast terminal sliding mode(GFTSM)-based model predictive torque control(MPTC)strategy is developed for permanent magnet synchronous motor(PMSM)drive system with only one phase current sensor.Generally two phase-current sensors are indispensable for MPTC.In response to only one phase current sensor available and the change of stator resistance,a novel adaptive observer for estimating the remaining two phase currents and time-varying stator resistance is proposed to perform MPTC.Moreover,in view of the variation of system parameters and external disturbance,a new GFTSM-based speed regulator is synthesized to enhance the drive system robustness.In this paper,the GFTSM,based on sliding mode theory,employs the fast terminal sliding mode in both the reaching stage and the sliding stage.The resultant GFTSM-based MPTC PMSM drive system with single phase current sensor has excellent dynamical performance which is very close to the GFTSM-based MPTC PMSM drive system with two-phase current sensors.On the other hand,compared with proportional-integral(PI)-based and sliding mode(SM)-based MPTC PMSM drive systems,it possesses better dynamical response and stronger robustness as well as smaller total harmonic distortion(THD)index of three-phase stator currents in the presence of variation of load torque.The simulation results validate the feasibility and effectiveness of the proposed scheme.展开更多
Motivated by the autopilot of an unmanned aerial vehicle（UAV） with a wide flight envelope span experiencing large parametric variations in the presence of uncertainties, a fuzzy adaptive tracking controller（FATC） ...Motivated by the autopilot of an unmanned aerial vehicle（UAV） with a wide flight envelope span experiencing large parametric variations in the presence of uncertainties, a fuzzy adaptive tracking controller（FATC） is proposed. The controller consists of a fuzzy baseline controller and an adaptive increment, and the main highlight is that the fuzzy baseline controller and adaptation laws are both based on the fuzzy multiple Lyapunov function approach, which helps to reduce the conservatism for the large envelope and guarantees satisfactory tracking performances with strong robustness simultaneously within the whole envelope. The constraint condition of the fuzzy baseline controller is provided in the form of linear matrix inequality（LMI）, and it specifies the satisfactory tracking performances in the absence of uncertainties. The adaptive increment ensures the uniformly ultimately bounded（UUB） predication errors to recover satisfactory responses in the presence of uncertainties. Simulation results show that the proposed controller helps to achieve high-accuracy tracking of airspeed and altitude desirable commands with strong robustness to uncertainties throughout the entire flight envelope.展开更多
Zn-based batteries have attracted extensive attention due to their high theoretical energy density,safety,abundant resources,environmental friendliness,and low cost.They are a new energy storage and conversion technol...Zn-based batteries have attracted extensive attention due to their high theoretical energy density,safety,abundant resources,environmental friendliness,and low cost.They are a new energy storage and conversion technology with significant development potential and have been widely used in renewable energy and portable electronic devices.Considerable attempts have been devoted to improving the performance of Zn-based batteries.Specifically,battery cycle life and energy efficiency can be improved by electrolyte modification and the construction of highly efficient rechargeable Zn anodes.This review compiles the progress of the research related to Zn anodes and electrolytes,especially in the last five years.This review will introduce fundamental concepts,summarize recent development,and inspire further systematic research for high-performance Zn-based batteries in the future.展开更多
When using deep belief networks(DBN)to establish a fault diagnosis model,the objective function easily falls into a local optimum during the learning and training process due to random initialization of the DBN networ...When using deep belief networks(DBN)to establish a fault diagnosis model,the objective function easily falls into a local optimum during the learning and training process due to random initialization of the DBN network bias and weights,thereby affecting the computational efficiency.To address the problem,a fault diagnosis method based on a deep belief network optimized by genetic algorithm(GA-DBN)is proposed.The method uses the restricted Boltzmann machine reconstruction error to structure the fitness function,and uses the genetic algorithm to optimize the network bias and weight,thus improving the network accuracy and convergence speed.In the experiment,the performance of the model is analyzed from the aspects of reconstruction error,classification accuracy,and time-consuming size.The results are compared with those of back propagation optimized by the genetic algorithm,support vector machines,and DBN.It shows that the proposed method improves the generalization ability of traditional DBN,and has higher recognition accuracy of photovoltaic array faults.展开更多
For an advanced aircraft,the amount of its effectors is much more than that for a traditional one,the functions of effectors are more complex and the coupling between each other is more severe.Based on the current con...For an advanced aircraft,the amount of its effectors is much more than that for a traditional one,the functions of effectors are more complex and the coupling between each other is more severe.Based on the current control allocation research,this paper puts forward the concept and framework of the control allocation and management system for aircrafts with redundancy con-trol effectors.A new optimal control allocation method,bases sequenced optimal(BSO)method,is then presented.By analyz-ing the physical meaning of the allocation process of BSO method,four types of management strategies are adopted by the system,which act on the control allocation process under different flight conditions,mission requirements and effectors work-ing conditions.Simulation results show that functions of the control allocation system are extended and the system adaptability to flight status,mission requirements and effector failure conditions is improved.展开更多
or a hypersonic flight vehicle with highly coupling nonlinear,a sliding mode controller based on reaching law is designed for its longitudinal motion model.Two proposals of reaching law are designed.One of which is a ...or a hypersonic flight vehicle with highly coupling nonlinear,a sliding mode controller based on reaching law is designed for its longitudinal motion model.Two proposals of reaching law are designed.One of which is a variable exponential reaching law,the other one is compound reaching law which consists of a conventional exponential reaching law and a power rate reaching law.The reaching law controller can speed up the system states arriving at the sliding mode condition,at the same time,it can guarantee better robustness.Simulation analysis is conducted for trimmed cruise condition of 110,000 ft and Mach 15,in which the responses of the vehicle to a step change of altitude and velocity respectively are analyzed.Simulation results show that the controller based on variable exponential reaching law enables the system to faster tracking speed than the conventional reaching law.Moreover the compound reaching law controller has shorter tracking time and strong robustness against parameters uncertainties.展开更多
文摘This paper refers to an integrated mCCHP （micro-combined cooling heat and power） systems dedicated for isolated residents with energetic independence. The only energy sources are wood pellet and solar energy. The proposed trigeneration system is based on mCHP （micro-combined heat and power） unit with Stirling engine, photovoltaic panels, thermal solar collector and pellet boiler. The proposed mCCHP system utilizes the exceeding amount of heat in the summer for producing the necessary cooling. A residential building with known energy consumption is determined load curves that must be covered by mCCHP system. The paper analyzes four structures of trigeneration systems with thermal activation chiller and two structures of trigeneration systems with mechanical compression chiller. Performance indicators are determined based on energy balance equations for each variant. It compares the performances and establishes the best option.
基金jointly supported by the Major Science and Technology Projects of Gansu Province(21ZD4FA020)the National Natural Science Foundation of China(42230720)the Leading Talents Program of Gansu Province(E339040101)
文摘Background Droughts likely lead to the decrease of vegetation coverage and plant productivity.Due to climate change,more extreme climatic events,including soil droughts and extreme temperatures,may occur both independently and simultaneously.Therefore,it is important to understand the thresholds of soil drought in order to avoid various undesired transitions of alpine grassland.Methods Soil droughts were identified based on the change of soil moisture,and vegetation coverage decline events were identified by the abnormal decrease of normalized difference vegetation index(NDVI).Three thresholds based on two curves of vegetation responses to soil drought illustrated the tipping points that reflected the rapid loss of ecosystem resistance(T_(p1)),the complete loss of ecosystem resistance(T_(p2))and the amplified magnitude of NDVI decrease(T_(m)).The influences of legacy effects and extreme temperatures were also considered.Results Alpine grasslands in northeastern Qinghai-Tibet Plateau had mean T_(p1),T_(p2)and T_(m)of 1.25,1.98 and 1.93,respectively,indicating low resistance and high vulnerability.T_(p1)was low for the most study area,and T_(p2)and Tmva ried with elevation and vegetation types.Besides the low occurrence of soil droughts coupled with high temperatures,the extremely low temperatures decreased 36%T_(p1),nearly all of T_(p2)and 30%T_(m).Different grassland types showed varying responses to soil droughts,with alpine sparse vegetation having the lowest resistance and alpine wetland having the highest.However,the responses according to soil types did not show obvious differences.Conclusions Alpine grasslands in northeastern Qinghai-Tibet Plateau were sensitive to soil droughts,and extremely low temperatures intensified the decrease of ecosystem resistance to soil drought.The identification of soil drought thresholds advances the understanding of how alpine grassland responds to soil droughts,and helps the restoration of alpine grasslands when faced with soil droughts and benefits climate adaptation.
基金supported by the National Natural Science Foundation of China (Grant No.61004089)
文摘Intensive studies have been carried out on generations of waverider geometry and hypersonic inlet geometry. However, integration efforts of waverider and related air-intake system are restricted majorly around the X43A-like or conical flow field induced configuration, which adopts mainly the two-dimensional air-breathing technology and limits the judicious visions of developing new aerodynamic profiles for hypersonic designers. A novel design approach for integrating the inward turning inlet with the traditional parameterized waverider is proposed. The proposed method is an alternative means to produce a compatible configuration by linking the off-the-shelf results on both traditional waverider techniques and inward turning inlet techniques. A series of geometry generations and optimization solutions is proposed to enhance the lift-to-drag ratio. A quantitative but efficient aerodynamic performance evaluation approach （the hypersonic flow panel method） with lower computational cost is employed to play the role of objective function for opti- mization purpose. The produced geometry compatibility with a computational fluid dynamics （CFD） solver is also verified for detailed flow field investigation. Optimization results and other numerical validations are obtained for the feasibility demonstration of the proposed method.
基金supported by the National Natural Science Foundation of China(61463025).
文摘A global fast terminal sliding mode(GFTSM)-based model predictive torque control(MPTC)strategy is developed for permanent magnet synchronous motor(PMSM)drive system with only one phase current sensor.Generally two phase-current sensors are indispensable for MPTC.In response to only one phase current sensor available and the change of stator resistance,a novel adaptive observer for estimating the remaining two phase currents and time-varying stator resistance is proposed to perform MPTC.Moreover,in view of the variation of system parameters and external disturbance,a new GFTSM-based speed regulator is synthesized to enhance the drive system robustness.In this paper,the GFTSM,based on sliding mode theory,employs the fast terminal sliding mode in both the reaching stage and the sliding stage.The resultant GFTSM-based MPTC PMSM drive system with single phase current sensor has excellent dynamical performance which is very close to the GFTSM-based MPTC PMSM drive system with two-phase current sensors.On the other hand,compared with proportional-integral(PI)-based and sliding mode(SM)-based MPTC PMSM drive systems,it possesses better dynamical response and stronger robustness as well as smaller total harmonic distortion(THD)index of three-phase stator currents in the presence of variation of load torque.The simulation results validate the feasibility and effectiveness of the proposed scheme.
文摘Motivated by the autopilot of an unmanned aerial vehicle（UAV） with a wide flight envelope span experiencing large parametric variations in the presence of uncertainties, a fuzzy adaptive tracking controller（FATC） is proposed. The controller consists of a fuzzy baseline controller and an adaptive increment, and the main highlight is that the fuzzy baseline controller and adaptation laws are both based on the fuzzy multiple Lyapunov function approach, which helps to reduce the conservatism for the large envelope and guarantees satisfactory tracking performances with strong robustness simultaneously within the whole envelope. The constraint condition of the fuzzy baseline controller is provided in the form of linear matrix inequality（LMI）, and it specifies the satisfactory tracking performances in the absence of uncertainties. The adaptive increment ensures the uniformly ultimately bounded（UUB） predication errors to recover satisfactory responses in the presence of uncertainties. Simulation results show that the proposed controller helps to achieve high-accuracy tracking of airspeed and altitude desirable commands with strong robustness to uncertainties throughout the entire flight envelope.
基金This work was financially supported by the National Natural Science Foundation of China(No.51925202 and 51972008).
文摘Zn-based batteries have attracted extensive attention due to their high theoretical energy density,safety,abundant resources,environmental friendliness,and low cost.They are a new energy storage and conversion technology with significant development potential and have been widely used in renewable energy and portable electronic devices.Considerable attempts have been devoted to improving the performance of Zn-based batteries.Specifically,battery cycle life and energy efficiency can be improved by electrolyte modification and the construction of highly efficient rechargeable Zn anodes.This review compiles the progress of the research related to Zn anodes and electrolytes,especially in the last five years.This review will introduce fundamental concepts,summarize recent development,and inspire further systematic research for high-performance Zn-based batteries in the future.
基金Supported by the National Key Research and Development Program of China(2017YFB1201003-020)the Science and Technology Project of Gansu Province(18YF1FA058).
文摘When using deep belief networks(DBN)to establish a fault diagnosis model,the objective function easily falls into a local optimum during the learning and training process due to random initialization of the DBN network bias and weights,thereby affecting the computational efficiency.To address the problem,a fault diagnosis method based on a deep belief network optimized by genetic algorithm(GA-DBN)is proposed.The method uses the restricted Boltzmann machine reconstruction error to structure the fitness function,and uses the genetic algorithm to optimize the network bias and weight,thus improving the network accuracy and convergence speed.In the experiment,the performance of the model is analyzed from the aspects of reconstruction error,classification accuracy,and time-consuming size.The results are compared with those of back propagation optimized by the genetic algorithm,support vector machines,and DBN.It shows that the proposed method improves the generalization ability of traditional DBN,and has higher recognition accuracy of photovoltaic array faults.
基金supported by the National Natural Science Foundation of China(Grant No.60804007)the Aviation Science Funds of China(Grant No.20080751018)
文摘For an advanced aircraft,the amount of its effectors is much more than that for a traditional one,the functions of effectors are more complex and the coupling between each other is more severe.Based on the current control allocation research,this paper puts forward the concept and framework of the control allocation and management system for aircrafts with redundancy con-trol effectors.A new optimal control allocation method,bases sequenced optimal(BSO)method,is then presented.By analyz-ing the physical meaning of the allocation process of BSO method,four types of management strategies are adopted by the system,which act on the control allocation process under different flight conditions,mission requirements and effectors work-ing conditions.Simulation results show that functions of the control allocation system are extended and the system adaptability to flight status,mission requirements and effector failure conditions is improved.
基金supported by the National Natural Science Foundation of China(91216304).
文摘or a hypersonic flight vehicle with highly coupling nonlinear,a sliding mode controller based on reaching law is designed for its longitudinal motion model.Two proposals of reaching law are designed.One of which is a variable exponential reaching law,the other one is compound reaching law which consists of a conventional exponential reaching law and a power rate reaching law.The reaching law controller can speed up the system states arriving at the sliding mode condition,at the same time,it can guarantee better robustness.Simulation analysis is conducted for trimmed cruise condition of 110,000 ft and Mach 15,in which the responses of the vehicle to a step change of altitude and velocity respectively are analyzed.Simulation results show that the controller based on variable exponential reaching law enables the system to faster tracking speed than the conventional reaching law.Moreover the compound reaching law controller has shorter tracking time and strong robustness against parameters uncertainties.
