Hydrogen evolution reaction(HER)catalytic electrodes under actual working conditions show interesting mass transfer behaviors at solid(electrode)/liquid(electrolyte)/gas(hydrogen)three-phase interfaces.These behaviors...Hydrogen evolution reaction(HER)catalytic electrodes under actual working conditions show interesting mass transfer behaviors at solid(electrode)/liquid(electrolyte)/gas(hydrogen)three-phase interfaces.These behaviors are essential for forming a continuous and effective physical contact region between the electrolyte and the electrode and require further detailed understanding.Here,a case study on 1 T-2 H phase molybdenum disulfide(Mo S_(2))/carbon fiber paper(CFP)catalytic electrodes is performed.Rapid gas-liquid mass transfer at the interface for enhancing the working area stability and capillarity for increasing the electrode working area is found.The real scenario,wherein the energy utilization efficiency of the as-prepared non-noble metal catalytic electrode exceeds that of the noble metal catalytic electrode,is disclosed.Specifically,a fluid dynamics model is developed to investigate the behavior mechanism of hydrogen bubbles from generation to desorption on the catalytic electrode surface with different hydrophilic and hydrophobic properties.These new insights and theoretical evidence on the non-negligible three-phase interface behaviors will identify opportunities and motivate future research in high-efficiency,stability,and low-cost HER catalytic electrode development.展开更多
Stabilizing the interface wave of the molten aluminum(metal)-electrolyte(bath)is beneficial to shorten the anode-cathode distance(ACD)which is critical to the energy saving.A coupled mathematical model was developed t...Stabilizing the interface wave of the molten aluminum(metal)-electrolyte(bath)is beneficial to shorten the anode-cathode distance(ACD)which is critical to the energy saving.A coupled mathematical model was developed to study the impact of the novel cathode protrusion on the molten fluid motion as well as the metal-bath interface deformation.The molten fluid motion in the aluminum reduction ceils is under the combined effect of the electro-magnetic forces(EMFs)and the gas bubbles generated at the anode.A transient inhomogeneous three-phase model(metal-bath-gas bubble)was established in order to calculate more accurate.The results indicate that the metal-bath interface deformation can be reduced significantly by the novel cathode protrusion which is beneficial to the electric energy saving.Besides,The EMFs decreases as a result of the optimizing of the magnetic field due to the novel cathode convex which is an important driving force for the deformation of the interface.In addition,large vortex in the metal flow field is break up into the small vortex by the cathode protrusion and then dissipated due to the viscous force and the hindering effect of the cathode protrusion.The quantity of the vortex as well as the strength of the vortex reduces significantly in the reduction cell with novel cathode protrusion.展开更多
The use of seawater-based electrolytes in zinc-air batteries(S-ZABs)presents significant economic and social benefits and mitigates the demand for scarce freshwater resources.However,it is challenging to achieve a met...The use of seawater-based electrolytes in zinc-air batteries(S-ZABs)presents significant economic and social benefits and mitigates the demand for scarce freshwater resources.However,it is challenging to achieve a metal^(-)nitrogen-carbon(M-N-C)catalyst that exhibits high resistance to corrosive Cl^(-)in seawater-based electrolytes and possesses a strengthened binding affinity with O_(2),which enables catalysts with an optimized oxygen reduction reaction(ORR)and enhances the applicability of S-ZABs.Herein,we propose a combined wet chemistry-pyrolysis strategy to obtain atomically dispersed Fe-decorated nitrogen-doped mesoporous carbon spheres(N-MCS-Fe-900).Benefiting from the capacity of the Fe decorations to form the edge-hosted aerophilic FeN_(4)-O_(2)sites at the optimized three-phase interface,N-MCS-Fe-900 affords the enhanced resistance of the active Fe sites to corrosive Cl^(-),as well as improved interaction with O_(2),thereby facilitating the ORR process.As expected,the N-MCS-Fe-900 delivers high half wave potential of 0.90 V and kinetic current density of 18.61 mA cm^(-2)at 0.85 V in seawater-based 0.1 M KOH.More importantly,the S-ZABs equipped with N-MCS-Fe-900 exhibited long-term stability under a high current density for over 140 h without voltage decay.Theoretical calculations and electrochemical performance evaluations collectively revealed the superior catalytic efficacy and genesis of this activity in N-MCS-Fe-900,which features edge-hosted FeN_(4)-O_(2)sites at the stable three-phase interface in seawater electrolytes.This study provides new insights for the advancement of ORR catalysts in sustainable energy conversion technologies for seawater-based electrolytes.展开更多
Membrane/solution interface consists of a neutral concentration polai layer(CPL) and a charge layer(CL) under external electrical field, and the neutral CPL can be neglected under high frequency AC electrical field. T...Membrane/solution interface consists of a neutral concentration polai layer(CPL) and a charge layer(CL) under external electrical field, and the neutral CPL can be neglected under high frequency AC electrical field. The relationship of CL thickness e with electrolyte concentration C and fixed ion exchange sites density σ in membrane surface layer can be expressed as e展开更多
A novel three-phase traction power supply system is proposed to eliminate the adverse effects caused by electric phase separation in catenary and accomplish a unifying manner of traction power supply for rail transit....A novel three-phase traction power supply system is proposed to eliminate the adverse effects caused by electric phase separation in catenary and accomplish a unifying manner of traction power supply for rail transit.With the application of two-stage three-phase continuous power supply structure,the electrical characteristics exhibit new features differing from the existing traction system.In this work,the principle for voltage levels determining two-stage network is dissected in accordance with the requirements of traction network and electric locomotive.The equivalent model of three-phase traction system is built for deducing the formula of current distribution and voltage losses.Based on the chain network model of the traction network,a simulation model is established to analyze the electrical characteristics such as traction current distribution,voltage losses,system equivalent impedance,voltage distribution,voltage unbalance and regenerative energy utilization.In a few words,quite a lot traction current of about 99%is undertaken by long-section cable network.The proportion of system voltage losses is small attributed to the two-stage three-phase power supply structure,and the voltage unbal-ance caused by impedance asymmetry of traction network is less than 1‰.In addition,the utilization rate of regenerative energy for locomotive achieves a significant promotion of over 97%.展开更多
Half-wavelength AC transmission(HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. It is very important for the constructi...Half-wavelength AC transmission(HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. It is very important for the construction and operation of HWACT to analyze its fault features and corresponding protection technology. In this paper, the steady-state voltage and current characteristics of the bus bar and fault point and the steady-state overvoltage distribution along the line will be analyzed when a three-phase symmetrical short-circuit fault occurs on an HWACT line. On this basis, the threephase fault characteristics for longer transmission lines are also studied.展开更多
The rapid development of new energy power generation technology and the transformation of power electronics in the core equipment of source-grid-load drives the power system towards the“double-high”development patte...The rapid development of new energy power generation technology and the transformation of power electronics in the core equipment of source-grid-load drives the power system towards the“double-high”development pattern of“high proportion of renewable energy”and“high proportion of power electronic equipment”.To enhance the transient performance of AC/DC hybrid microgrid(HMG)in the context of“double-high,”aπtype virtual synchronous generator(π-VSG)control strategy is applied to bidirectional interface converter(BIC)to address the issues of lacking inertia and poor disturbance immunity caused by the high penetration rate of power electronic equipment and new energy.Firstly,the virtual synchronous generator mechanical motion equations and virtual capacitance equations are used to introduce the virtual inertia control equations that consider the transient performance of HMG;based on the equations,theπ-type equivalent control model of the BIC is established.Next,the inertia power is actively transferred through the BIC according to the load fluctuation to compensate for the system’s inertia deficit.Secondly,theπ-VSG control utilizes small-signal analysis to investigate howthe fundamental parameters affect the overall stability of the HMG and incorporates power step response curves to reveal the relationship between the control’s virtual parameters and transient performance.Finally,the PSCAD/EMTDC simulation results show that theπ-VSG control effectively improves the immunity of AC frequency and DC voltage in the HMG system under the load fluctuation condition,increases the stability of the HMG system and satisfies the power-sharing control objective between the AC and DC subgrids.展开更多
This paper focuses on the direct current-alternating current （DC-AC） interfaced microsource based H∞ robust control strategies in microgrids. It presents detail of a DC-AC interfaced microsource model which is conn...This paper focuses on the direct current-alternating current （DC-AC） interfaced microsource based H∞ robust control strategies in microgrids. It presents detail of a DC-AC interfaced microsource model which is connected to the power grid through a controllable switch. A double loop current-regulated voltage control scheme for the DC-AC interface is designed. In the case of the load disturbance and the model uncertainties, the inner voltage and current loop are produced based on the H∞ robust control strategies. The outer power loop uses the droop characteristic controller. Finally, the scheme is simulated using the Matlab/Simulink. The simulation results demonstrate that DC-AC interfaced microsource system can supply high quality power. Also, the proposed control scheme can make the system switch smoothly between the isolated mode and grid-connected mode. 更多展开更多
Inspired by the dynamic wet adhesive systems in nature,various artificial adhesive surfaces have been developed but still face different challenges.Crucially,the theoretical mechanics of wet adhesives has never been s...Inspired by the dynamic wet adhesive systems in nature,various artificial adhesive surfaces have been developed but still face different challenges.Crucially,the theoretical mechanics of wet adhesives has never been sufficiently revealed.Here,we develop a novel adhesive mechanism for governing wet adhesion and investigate the biological models of honeybee arolium for reproducing the natural wet adhesive systems.Micro-nano structures of honeybee arolium and arolium-prints were observed by Cryogenic scanning electron microscopy(Cryo-SEM),and the air pockets were found in the contact interface notably.Subsequently,the adhesive models with a three-phase composite interface(including air pockets,liquid secretion,and hexagonal frames of arolium),were formed to analyze the wet adhesion of honeybee arolium.The results of theoretical calculations and experiments indicated an enhanced adhesive mechanism of the honeybee by liquid self-sucking effects and air-embolism effects.Under these effects,normal and shear adhesion can be adjusted by controlling the proportion of liquid secretion and air pockets in the contact zone.Notably,the air-embolism effects contribute to the optimal coupling of smaller normal adhesion with greater shear adhesion,which is beneficial for the high stride frequency of honeybees.These works can provide a fresh perspective on the development of bio-inspired wet adhesive surfaces.展开更多
This paper proposes a multiport bidirectional non-isolated converter topology that provides advantages in terms of simultaneous multiple operations,single-stage conversion,high power density and reduced power losses d...This paper proposes a multiport bidirectional non-isolated converter topology that provides advantages in terms of simultaneous multiple operations,single-stage conversion,high power density and reduced power losses due to the lower number of switches.The proposed multiport converter uses a centralized non-linear controller known as a finite control set model predictive controller to manage the flow of power between different ports.It deals with the parallel operation of photovoltaic and battery energy storage systems for stand-alone alternating current(AC)systems.The converter connects the lower voltage battery to the photovoltaic port using a bidirectional buck/boost converter and the photovoltaic port is linked to the stand-alone AC load through a three-phase full-bridge inverter.Each leg of the three-phase converter will act as a bidirectional direct current(DC)/DC converter as well as an inverter simultaneously.Only six switches manage the power transfer between all the connected ports of photovoltaic-battery energy storage system linked to the stand-alone AC load.The proposed multiport converter is mathematically modelled and controlled by a finite control set model predictive controller.The system is validated in simulation(1-kW rating)and experimental environment(200-W rating).The hardware prototype is developed in the laboratory and the controller is implemented on the field-programmable gate array board.Two independent case studies are carried out to validate the efficacy of the system.The first scenario is for a change in solar irradiance,while the second scenario is for a change in the output load.展开更多
This paper focuses on a combination of three-phase VSI （voltage source inverter） with a predictive current control to provide an optimized system for three-phase inverters that control the load current. A FS-MPC （f...This paper focuses on a combination of three-phase VSI （voltage source inverter） with a predictive current control to provide an optimized system for three-phase inverters that control the load current. A FS-MPC （finite set-model predictive control） strategy for a three-phase VSI for RES （renewable energy systems） applications is implemented. The renewable energy systems model is used in this paper to investigate the system performance when power is supplied to resistive-inductive load. With three different cases, the evaluation of the system is done. Firstly, the robustness of control strategy under variable DC-Link is done in terms of the THD （total harmonic distortion）. Secondly, with one prediction step, the system performance is tested using different sampling time, and lastly, the dynamic response of the system with step change in the amplitude of the reference is investigated. The simulations and result analyses are carried out using Matlab/Simulink to test the effectiveness and robustness of FS-MPC for two-level VSI with AC filter for resistive-inductive load supplied by a renewable energy system.展开更多
The coordinated control of parallel three-phase fourwire converters in autonomous AC microgrids is investigated in this paper.First,based on droop control,virtual impedance is inserted in positive-,negative-and zero-s...The coordinated control of parallel three-phase fourwire converters in autonomous AC microgrids is investigated in this paper.First,based on droop control,virtual impedance is inserted in positive-,negative-and zero-sequences to enhance system damping and imbalance power sharing.Then,to facilitate virtual impedance design,small signal models of the three-sequence equivalent circuits are established respectively.Corresponding indexes are proposed to comprehensively evaluate the impact of sequence virtual impedance on current sharing accuracy,voltage quality at the point of common coupling(PCC)and system stability.In addition,constraint of DClink voltage is also considered to avoid over modulation when subjected to unbalanced loads.Furthermore,to address the PCC voltage degradation resulting from virtual impedance,a voltage imbalance compensation method,based on low-bandwidth communication,is proposed.Finally,simulation and experimental results are provided to verify the correctness of the theory model,indicating that the proposed method can achieve PCC voltage restoration while guaranteeing the current sharing accuracy with desirable dynamics.展开更多
Substantial progress has been made in the understanding of gas-involving electrochemical reactions recently for the sake of clean,renewable,and efficient energy technologies.However,the specific influence mechanism of...Substantial progress has been made in the understanding of gas-involving electrochemical reactions recently for the sake of clean,renewable,and efficient energy technologies.However,the specific influence mechanism of the microenvironment at the reaction interface on the electrocatalytic performance(activity,selectivity,and durability)remains unclear.Here,we provide a comprehensive understanding of the interfacial microenvironment of gas-involving electrocatalysis,including carbon dioxide reduction reaction and nitrogen reduction reaction,and classify the factors affecting the reaction thermodynamics and kinetics into gas diffusion,proton supply,and electron transfer.This categorization allows a systematic survey of the literature focusing on electrolyzer-level(optimization of the device,control of the experimental condition,and design of the working electrode),electrolytelevel(increase of gas solubility,regulation of proton supply,and substitution of anodic reaction),and electrocatalyst-level strategies(promotion of gas affinity,adjustment of hydrophobicity,and enhancement of conductivity),aiming to retrieve the correlations between the microenvironment and electrochemical performance.Finally,priorities for future studies are suggested to support the comprehensive improvement of next-generation gas-involving electrochemical reactions.展开更多
基金supported by the National Natural Science Foundation of China(No.62004051)the Natural Science Foundation of Heilongjiang province(No.LH2020F013)+1 种基金the China Postdoctoral Science Fund(No.2020M670909)the Heilongjiang Postdoctoral Science Fund(No.LBH-Z19017)。
文摘Hydrogen evolution reaction(HER)catalytic electrodes under actual working conditions show interesting mass transfer behaviors at solid(electrode)/liquid(electrolyte)/gas(hydrogen)three-phase interfaces.These behaviors are essential for forming a continuous and effective physical contact region between the electrolyte and the electrode and require further detailed understanding.Here,a case study on 1 T-2 H phase molybdenum disulfide(Mo S_(2))/carbon fiber paper(CFP)catalytic electrodes is performed.Rapid gas-liquid mass transfer at the interface for enhancing the working area stability and capillarity for increasing the electrode working area is found.The real scenario,wherein the energy utilization efficiency of the as-prepared non-noble metal catalytic electrode exceeds that of the noble metal catalytic electrode,is disclosed.Specifically,a fluid dynamics model is developed to investigate the behavior mechanism of hydrogen bubbles from generation to desorption on the catalytic electrode surface with different hydrophilic and hydrophobic properties.These new insights and theoretical evidence on the non-negligible three-phase interface behaviors will identify opportunities and motivate future research in high-efficiency,stability,and low-cost HER catalytic electrode development.
基金Item Sponsored by the National Natural Science Foundation of China[NO.50934005 and NO.50904014]
文摘Stabilizing the interface wave of the molten aluminum(metal)-electrolyte(bath)is beneficial to shorten the anode-cathode distance(ACD)which is critical to the energy saving.A coupled mathematical model was developed to study the impact of the novel cathode protrusion on the molten fluid motion as well as the metal-bath interface deformation.The molten fluid motion in the aluminum reduction ceils is under the combined effect of the electro-magnetic forces(EMFs)and the gas bubbles generated at the anode.A transient inhomogeneous three-phase model(metal-bath-gas bubble)was established in order to calculate more accurate.The results indicate that the metal-bath interface deformation can be reduced significantly by the novel cathode protrusion which is beneficial to the electric energy saving.Besides,The EMFs decreases as a result of the optimizing of the magnetic field due to the novel cathode convex which is an important driving force for the deformation of the interface.In addition,large vortex in the metal flow field is break up into the small vortex by the cathode protrusion and then dissipated due to the viscous force and the hindering effect of the cathode protrusion.The quantity of the vortex as well as the strength of the vortex reduces significantly in the reduction cell with novel cathode protrusion.
基金supported by the National Natural Science Foundation of China(22309197,22279124,and 52261145700)the Natural Science Foundation of Shandong Province(ZR2022ZD30).
文摘The use of seawater-based electrolytes in zinc-air batteries(S-ZABs)presents significant economic and social benefits and mitigates the demand for scarce freshwater resources.However,it is challenging to achieve a metal^(-)nitrogen-carbon(M-N-C)catalyst that exhibits high resistance to corrosive Cl^(-)in seawater-based electrolytes and possesses a strengthened binding affinity with O_(2),which enables catalysts with an optimized oxygen reduction reaction(ORR)and enhances the applicability of S-ZABs.Herein,we propose a combined wet chemistry-pyrolysis strategy to obtain atomically dispersed Fe-decorated nitrogen-doped mesoporous carbon spheres(N-MCS-Fe-900).Benefiting from the capacity of the Fe decorations to form the edge-hosted aerophilic FeN_(4)-O_(2)sites at the optimized three-phase interface,N-MCS-Fe-900 affords the enhanced resistance of the active Fe sites to corrosive Cl^(-),as well as improved interaction with O_(2),thereby facilitating the ORR process.As expected,the N-MCS-Fe-900 delivers high half wave potential of 0.90 V and kinetic current density of 18.61 mA cm^(-2)at 0.85 V in seawater-based 0.1 M KOH.More importantly,the S-ZABs equipped with N-MCS-Fe-900 exhibited long-term stability under a high current density for over 140 h without voltage decay.Theoretical calculations and electrochemical performance evaluations collectively revealed the superior catalytic efficacy and genesis of this activity in N-MCS-Fe-900,which features edge-hosted FeN_(4)-O_(2)sites at the stable three-phase interface in seawater electrolytes.This study provides new insights for the advancement of ORR catalysts in sustainable energy conversion technologies for seawater-based electrolytes.
基金Project(02-09-01) supported by Panzhihua Iron and Steel Corporation,China
文摘Membrane/solution interface consists of a neutral concentration polai layer(CPL) and a charge layer(CL) under external electrical field, and the neutral CPL can be neglected under high frequency AC electrical field. The relationship of CL thickness e with electrolyte concentration C and fixed ion exchange sites density σ in membrane surface layer can be expressed as e
基金This research was supported by the Science and Technology Plan Project of Sichuan Province(No.21YYJC3324)the Science and Technology Plan Project of Sichuan Province(No.2022YFQ0104).
文摘A novel three-phase traction power supply system is proposed to eliminate the adverse effects caused by electric phase separation in catenary and accomplish a unifying manner of traction power supply for rail transit.With the application of two-stage three-phase continuous power supply structure,the electrical characteristics exhibit new features differing from the existing traction system.In this work,the principle for voltage levels determining two-stage network is dissected in accordance with the requirements of traction network and electric locomotive.The equivalent model of three-phase traction system is built for deducing the formula of current distribution and voltage losses.Based on the chain network model of the traction network,a simulation model is established to analyze the electrical characteristics such as traction current distribution,voltage losses,system equivalent impedance,voltage distribution,voltage unbalance and regenerative energy utilization.In a few words,quite a lot traction current of about 99%is undertaken by long-section cable network.The proportion of system voltage losses is small attributed to the two-stage three-phase power supply structure,and the voltage unbal-ance caused by impedance asymmetry of traction network is less than 1‰.In addition,the utilization rate of regenerative energy for locomotive achieves a significant promotion of over 97%.
基金supported by National Key Research and Development Program of China(2016YFB0900100)
文摘Half-wavelength AC transmission(HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. It is very important for the construction and operation of HWACT to analyze its fault features and corresponding protection technology. In this paper, the steady-state voltage and current characteristics of the bus bar and fault point and the steady-state overvoltage distribution along the line will be analyzed when a three-phase symmetrical short-circuit fault occurs on an HWACT line. On this basis, the threephase fault characteristics for longer transmission lines are also studied.
基金funded by“The Fourth Phase of 2022 Advantage Discipline Engineering-Control Science and Engineering”,grant number 4013000063.
文摘The rapid development of new energy power generation technology and the transformation of power electronics in the core equipment of source-grid-load drives the power system towards the“double-high”development pattern of“high proportion of renewable energy”and“high proportion of power electronic equipment”.To enhance the transient performance of AC/DC hybrid microgrid(HMG)in the context of“double-high,”aπtype virtual synchronous generator(π-VSG)control strategy is applied to bidirectional interface converter(BIC)to address the issues of lacking inertia and poor disturbance immunity caused by the high penetration rate of power electronic equipment and new energy.Firstly,the virtual synchronous generator mechanical motion equations and virtual capacitance equations are used to introduce the virtual inertia control equations that consider the transient performance of HMG;based on the equations,theπ-type equivalent control model of the BIC is established.Next,the inertia power is actively transferred through the BIC according to the load fluctuation to compensate for the system’s inertia deficit.Secondly,theπ-VSG control utilizes small-signal analysis to investigate howthe fundamental parameters affect the overall stability of the HMG and incorporates power step response curves to reveal the relationship between the control’s virtual parameters and transient performance.Finally,the PSCAD/EMTDC simulation results show that theπ-VSG control effectively improves the immunity of AC frequency and DC voltage in the HMG system under the load fluctuation condition,increases the stability of the HMG system and satisfies the power-sharing control objective between the AC and DC subgrids.
基金supported by National Natural Science Foundation of China(No. 51177142)China Postdoctoral Science Foundation(Nos.2012T50019 and 20110490210)Hebei Provincial Natural Science Foundation of China(No.F2012203063)
文摘This paper focuses on the direct current-alternating current （DC-AC） interfaced microsource based H∞ robust control strategies in microgrids. It presents detail of a DC-AC interfaced microsource model which is connected to the power grid through a controllable switch. A double loop current-regulated voltage control scheme for the DC-AC interface is designed. In the case of the load disturbance and the model uncertainties, the inner voltage and current loop are produced based on the H∞ robust control strategies. The outer power loop uses the droop characteristic controller. Finally, the scheme is simulated using the Matlab/Simulink. The simulation results demonstrate that DC-AC interfaced microsource system can supply high quality power. Also, the proposed control scheme can make the system switch smoothly between the isolated mode and grid-connected mode. 更多
基金supported by the National Key R&D Program of China(2021YFB3400200)the Beijing Natural Science Foundation(3212012)+2 种基金the National Natural Science Foundation of China(52075038)the Opening Project of the Key Laboratory of Bionic Engineering(Ministry of Education),Jilin University(KF20200001)the Opening Project of State Key Laboratory of Tribology,Tsinghua University(SKLTKF20B06)。
文摘Inspired by the dynamic wet adhesive systems in nature,various artificial adhesive surfaces have been developed but still face different challenges.Crucially,the theoretical mechanics of wet adhesives has never been sufficiently revealed.Here,we develop a novel adhesive mechanism for governing wet adhesion and investigate the biological models of honeybee arolium for reproducing the natural wet adhesive systems.Micro-nano structures of honeybee arolium and arolium-prints were observed by Cryogenic scanning electron microscopy(Cryo-SEM),and the air pockets were found in the contact interface notably.Subsequently,the adhesive models with a three-phase composite interface(including air pockets,liquid secretion,and hexagonal frames of arolium),were formed to analyze the wet adhesion of honeybee arolium.The results of theoretical calculations and experiments indicated an enhanced adhesive mechanism of the honeybee by liquid self-sucking effects and air-embolism effects.Under these effects,normal and shear adhesion can be adjusted by controlling the proportion of liquid secretion and air pockets in the contact zone.Notably,the air-embolism effects contribute to the optimal coupling of smaller normal adhesion with greater shear adhesion,which is beneficial for the high stride frequency of honeybees.These works can provide a fresh perspective on the development of bio-inspired wet adhesive surfaces.
文摘This paper proposes a multiport bidirectional non-isolated converter topology that provides advantages in terms of simultaneous multiple operations,single-stage conversion,high power density and reduced power losses due to the lower number of switches.The proposed multiport converter uses a centralized non-linear controller known as a finite control set model predictive controller to manage the flow of power between different ports.It deals with the parallel operation of photovoltaic and battery energy storage systems for stand-alone alternating current(AC)systems.The converter connects the lower voltage battery to the photovoltaic port using a bidirectional buck/boost converter and the photovoltaic port is linked to the stand-alone AC load through a three-phase full-bridge inverter.Each leg of the three-phase converter will act as a bidirectional direct current(DC)/DC converter as well as an inverter simultaneously.Only six switches manage the power transfer between all the connected ports of photovoltaic-battery energy storage system linked to the stand-alone AC load.The proposed multiport converter is mathematically modelled and controlled by a finite control set model predictive controller.The system is validated in simulation(1-kW rating)and experimental environment(200-W rating).The hardware prototype is developed in the laboratory and the controller is implemented on the field-programmable gate array board.Two independent case studies are carried out to validate the efficacy of the system.The first scenario is for a change in solar irradiance,while the second scenario is for a change in the output load.
文摘This paper focuses on a combination of three-phase VSI （voltage source inverter） with a predictive current control to provide an optimized system for three-phase inverters that control the load current. A FS-MPC （finite set-model predictive control） strategy for a three-phase VSI for RES （renewable energy systems） applications is implemented. The renewable energy systems model is used in this paper to investigate the system performance when power is supplied to resistive-inductive load. With three different cases, the evaluation of the system is done. Firstly, the robustness of control strategy under variable DC-Link is done in terms of the THD （total harmonic distortion）. Secondly, with one prediction step, the system performance is tested using different sampling time, and lastly, the dynamic response of the system with step change in the amplitude of the reference is investigated. The simulations and result analyses are carried out using Matlab/Simulink to test the effectiveness and robustness of FS-MPC for two-level VSI with AC filter for resistive-inductive load supplied by a renewable energy system.
文摘The coordinated control of parallel three-phase fourwire converters in autonomous AC microgrids is investigated in this paper.First,based on droop control,virtual impedance is inserted in positive-,negative-and zero-sequences to enhance system damping and imbalance power sharing.Then,to facilitate virtual impedance design,small signal models of the three-sequence equivalent circuits are established respectively.Corresponding indexes are proposed to comprehensively evaluate the impact of sequence virtual impedance on current sharing accuracy,voltage quality at the point of common coupling(PCC)and system stability.In addition,constraint of DClink voltage is also considered to avoid over modulation when subjected to unbalanced loads.Furthermore,to address the PCC voltage degradation resulting from virtual impedance,a voltage imbalance compensation method,based on low-bandwidth communication,is proposed.Finally,simulation and experimental results are provided to verify the correctness of the theory model,indicating that the proposed method can achieve PCC voltage restoration while guaranteeing the current sharing accuracy with desirable dynamics.
基金National Natural Science Foundationof China,Grant/Award Numbers:U21A20332,52103226,52071226Outstanding Youth Foundation of Jiangsu Province,Grant/Award Number:BK20220061+2 种基金Natural Science Foundation of Jiangsu Province,Grant/Award Number:BK20201171Key Research and Development Plan of Jiangsu Province,Grant/Award Number:BE2020003-3Fellowship of China Postdoctoral Science Foundation,Grant/Award Number:2021M702382。
文摘Substantial progress has been made in the understanding of gas-involving electrochemical reactions recently for the sake of clean,renewable,and efficient energy technologies.However,the specific influence mechanism of the microenvironment at the reaction interface on the electrocatalytic performance(activity,selectivity,and durability)remains unclear.Here,we provide a comprehensive understanding of the interfacial microenvironment of gas-involving electrocatalysis,including carbon dioxide reduction reaction and nitrogen reduction reaction,and classify the factors affecting the reaction thermodynamics and kinetics into gas diffusion,proton supply,and electron transfer.This categorization allows a systematic survey of the literature focusing on electrolyzer-level(optimization of the device,control of the experimental condition,and design of the working electrode),electrolytelevel(increase of gas solubility,regulation of proton supply,and substitution of anodic reaction),and electrocatalyst-level strategies(promotion of gas affinity,adjustment of hydrophobicity,and enhancement of conductivity),aiming to retrieve the correlations between the microenvironment and electrochemical performance.Finally,priorities for future studies are suggested to support the comprehensive improvement of next-generation gas-involving electrochemical reactions.
