Zinc ion hybrid capacitors(ZIHCs),which integrate the features of the high power of supercapacitors and the high energy of zinc ion batteries,are promising competitors in future electrochemical energy storage applicat...Zinc ion hybrid capacitors(ZIHCs),which integrate the features of the high power of supercapacitors and the high energy of zinc ion batteries,are promising competitors in future electrochemical energy storage applications.Carbon-based materials are deemed the competitive candidates for cathodes of ZIHC due to their cost-effectiveness,high electronic conductivity,chemical inertness,controllable surface states,and tunable pore architectures.In recent years,great research efforts have been devoted to further improving the energy density and cycling stability of ZIHCs.Reasonable modification and optimization of carbon-based materials offer a remedy for these challenges.In this review,the structural design,and electrochemical properties of carbon-based cathode materials with different dimensions,as well as the selection of compatible,robust current collectors and separators for ZIHCs are discussed.The challenges and prospects of ZIHCs are showcased to guide the innovative development of carbon-based cathode materials and the development of novel ZIHCs.展开更多
The current collector is an indispensable component in potassium-ion hybrid capacitors,which not only provides mechanical support to load electrode materials,but also collects and outputs the current generated.Herein,...The current collector is an indispensable component in potassium-ion hybrid capacitors,which not only provides mechanical support to load electrode materials,but also collects and outputs the current generated.Herein,we investigate the effect of three different current collectors on the electrochemical properties of potassium ion capacitors using carbon black anode as a demonstration.Because of better adhesion and lower charge transfer resistance,the specific capacity of half-cells assembled using three-dimensional(3D)porous copper foil(PCu)and copper as current collector is better than that of Al foil,which stabilizes at 138.2 and 132.8 mAh·g^(-1)after 100 cycles at 0.05 A·g^(-1).The potassium-ion capacitor assembled using PCu exhibits an excellent energy/power density of 86.1 Wh·kg^(-1)and 4000 W·kg^(-1),respectively.This work will boost the rational design and provide an effective strategy to improve the performance of potassium-ion capacitors.展开更多
Objective For the inverters used in UPS, it is important to maintain the pure sinusoidal AC output voltage waveform over all loading conditions and transients. Methods A novel sinusoidal output voltage control strat...Objective For the inverters used in UPS, it is important to maintain the pure sinusoidal AC output voltage waveform over all loading conditions and transients. Methods A novel sinusoidal output voltage control strategy is pregented in this paper. The output voltage is controlled by introducing filtering eapacitor current feedback. Two simple PI regulators are used for the current and voltage control loops. Results With the new control strategy, the inverter achieves very low output voltage distortion, good output voltage regulation and strong perturbation rejection, fast dynamic response, and good performance under nonlinear loads. The THD under capacitance rectifying load is better than 0.2%, the output voltage regulation within 0 to full load is less than 0.1%. The resting time under load transient is within 200?μ s . Conclusion The merits of the new control strategy include rapid response and good steady state stiffness.展开更多
To miniaturize a very low level dc current amplifier and to improve its output response speed, the switched capacitor negative feedback circuit (SCNF), instead of the conventionally used high-ohmage resistor, is prese...To miniaturize a very low level dc current amplifier and to improve its output response speed, the switched capacitor negative feedback circuit (SCNF), instead of the conventionally used high-ohmage resistor, is presented in this paper. In our system, a switched capacitor filter (SCF) and an offset controller are also used to decrease vibrations and offset voltage at the output of the amplifier using SCNF. The theoretical output voltage of the very low level dc current amplifier using SCNF is obtained. The experimental results show that the unnecessary components of the amplifier’s output are much decreased, and that the response speed of the amplifier with both the SCNF and SCF is faster than that using high-ohmage resistor.展开更多
In this paper,an interleaved LCLC converter with enhancement-mode(E-mode)GaN devices is introduced to achieve the accurate current sharing performance for data center applications. Any tolerance in the resonant tank e...In this paper,an interleaved LCLC converter with enhancement-mode(E-mode)GaN devices is introduced to achieve the accurate current sharing performance for data center applications. Any tolerance in the resonant tank elements can lead to large load imbalance between any two different phases. Due to the steep gain curves of LCLC converters,conventional current sharing methods are not effective. In the proposed converter,the impedances of the resonant networks are matched by switching a capacitor,i.e.,switch controlled capacitor(SCC),in series with the resonant capacitor in one or some of the phases,which results in accurate load current sharing among the phases with an accuracy around 0.025%. The load share of a phase is sensed through the resonant current on it,and the control logic applied to such current sharing can be achieved. By this method,accurate current sharing is achieved for a wide input voltage range required for the hold-up time in data center applications. Interleaving is applied in the proposed multiphase LCLC converter,resulting in low current stress on the output capacitor and allowing ceramic capacitor implementation. Moreover,phase shedding accomplishes high light load efficiency. The performance of the proposed interleaved LCLC converter is verified by a two-phase 1 k W prototype with an input voltage ranging from 250 V to 400 V and a fixed 12 V output voltage.展开更多
Supercapacitors,comprising electrical double-layer capacitors(EDLCs)and pseudocapa-citors,are widely acknowledged as high-power energy storage devices.However,their local structures and fundamental mechanisms remain p...Supercapacitors,comprising electrical double-layer capacitors(EDLCs)and pseudocapa-citors,are widely acknowledged as high-power energy storage devices.However,their local structures and fundamental mechanisms remain poorly understood,and suitable experimental techniques for investigation are also lacking.Recently,nuclear magnetic resonance(NMR)has emerged as a powerful tool for addressing these fundamental issues with high local sensitivity and non-invasiveness.In this paper,we first review the limi-tations of existing characterization methods and highlight the advantages of NMR in investigating mechanisms of supercapacitors.Subsequently,we introduce the basic prin-ciple of ring current effect,NMR-active nuclei,and various NMR techniques employed in exploring energy storage mechanisms including cross polarization(CP)magic angle spinning(MAS)NMR,multiple-quantum(MQ)MAS,two-dimensional exchange spec-troscopy(2D-EXSY)NMR,magnetic resonance imaging(MRI)and pulsed-field gradient(PFG)NMR.Based on this,recent progress in investigating energy storage mechanisms in EDLCs and pseudocapacitors through various NMR techniques is discussed.Finally,an outlook on future directions for NMR research in supercapacitors is offered.展开更多
Growth and passivation of tunnels within Al foil by on-off controlling DC etching in 6 wt.% HCI solution has been investigated. It was found that, in a given etchant solution at a special temperature, the longest tunn...Growth and passivation of tunnels within Al foil by on-off controlling DC etching in 6 wt.% HCI solution has been investigated. It was found that, in a given etchant solution at a special temperature, the longest tunnel length was only a function of the turn-on interval of DC. The potential of Al foil broke at on-off controlling DC by the result from anode polarization curves and potential-time （E-t） responding curves. When DC was switched on, the potential increased abruptly over pitting potential, leading to nucleation of pits at the surface and the growth of tunnels at special length. When DC was switched off, the potential decreased rapidly to a passive value, leading to stoppage of nucleation and death of tunnels. By this way, the longest tunnel length can be controlled and a non-piercing layer can be obtained. Hence, etching of Al foil at this current is beneficial for maintaining a good mechanical strength.展开更多
The pulse-width-modulated(PWM)current-source converters(CSCs)fed electric machine systems can be considered as a type of high reliability energy conversion systems,since they work with the long-life DC-link inductor a...The pulse-width-modulated(PWM)current-source converters(CSCs)fed electric machine systems can be considered as a type of high reliability energy conversion systems,since they work with the long-life DC-link inductor and offer high fault-tolerant capability for short-circuit faults.Besides,they provide motor friendly waveforms and four-quadrant operation ability.Therefore,they are suitable for high-power applications of fans,pumps,compressors and wind power generation.The purpose of this paper is to comprehensively review recent developments of key technologies on modulation and control of high-power(HP)PWM-CSC fed electric machines systems,including reduction of low-order current harmonics,suppression of inductor–capacitor(LC)resonance,mitigation of common-mode voltage(CMV)and control of modular PWM-CSC fed systems.In particular,recent work on the overlapping effects during commutation,LC resonance suppression under fault-tolerant operation and collaboration of modular PMW-CSCs are described.Both theoretical analysis and some results in simulations and experiments are presented.Finally,a brief discussion regarding the future trend of the HP CSC fed electric machines systems is presented.展开更多
Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability ...Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability reduction.In order to solve these problems,a finite control set model predictive control(FCS-MPC)for FSTP AC-DC converters with DC-link capacitor voltage balancing is proposed.In this strategy,in order to facilitate calculation,theαβcoordinate system model is established and all voltage vectors are evaluated by establishing a cost function.During the whole process,phase locked loop(PLL)and complex modulation strategy are not required.In the new established cost function,the additional objective term of suppressing capacitor voltage fluctuation is to eliminate effectively the capacitor voltages oscillations and deviations and improve the system reliability.The simulation results show that the proposed strategy can keep the capacitor voltage balancing and has good dynamic and static performance.展开更多
The paper reports that Hfrio dielectric is deposited by reactive co-sputtering of Hf and Ti targets in an Ar/O2 ambience, followed by an annealing in different gas ambiences of N2, NO and NH3 at 600℃ for 2 min. Capac...The paper reports that Hfrio dielectric is deposited by reactive co-sputtering of Hf and Ti targets in an Ar/O2 ambience, followed by an annealing in different gas ambiences of N2, NO and NH3 at 600℃ for 2 min. Capacitancevoltage and gate-leakage properties are characterized and compared. The results indicate that the NO-annealed sample exhibits the lowest interface-state and dielectric-charge densities and best device reliability. This is attributed to the fact that nitridation can create strong Si≡N bonds to passivate dangling Si bonds and replace strained Si-O bonds, thus the sample forms a hardened dielectric/Si interface with high reliability.展开更多
基金the financial support from the National Natural Science Foundation of China(22108044)the 111 Project(B20088)+3 种基金the Fundamental Research Funds for the Central Universities(2572022DJ02)the Research and Development Program in Key Fields of Guangdong Province(2020B1111380002)the Basic Research and Applicable Basic Research in Guangzhou City(202201010290)the Guangdong Provincial Key Laboratory of Plant Resources Biorefinery(2021GDKLPRB07)。
文摘Zinc ion hybrid capacitors(ZIHCs),which integrate the features of the high power of supercapacitors and the high energy of zinc ion batteries,are promising competitors in future electrochemical energy storage applications.Carbon-based materials are deemed the competitive candidates for cathodes of ZIHC due to their cost-effectiveness,high electronic conductivity,chemical inertness,controllable surface states,and tunable pore architectures.In recent years,great research efforts have been devoted to further improving the energy density and cycling stability of ZIHCs.Reasonable modification and optimization of carbon-based materials offer a remedy for these challenges.In this review,the structural design,and electrochemical properties of carbon-based cathode materials with different dimensions,as well as the selection of compatible,robust current collectors and separators for ZIHCs are discussed.The challenges and prospects of ZIHCs are showcased to guide the innovative development of carbon-based cathode materials and the development of novel ZIHCs.
基金financially supported by the National Key Research and Development Program of China(No.2017YFE0198100)the National Natural Science Foundation of China(Nos.52072145 and 51802111)+4 种基金the Research Program on Science and Technology from the Education Department of Jilin Province(Nos.JJKH20220439KJ and JJKH20210450KJ)Jilin Talent Development Funding(No.2021Y027)the Funding of Jilin Province Development and Reform Commission(No.2020C026-2)Special Projects of the Central Government in Guidance of Local Science and Technology Development(No.202002017JC)Funding of JLNU Innovation Program for Graduate Education(No.202016)。
文摘The current collector is an indispensable component in potassium-ion hybrid capacitors,which not only provides mechanical support to load electrode materials,but also collects and outputs the current generated.Herein,we investigate the effect of three different current collectors on the electrochemical properties of potassium ion capacitors using carbon black anode as a demonstration.Because of better adhesion and lower charge transfer resistance,the specific capacity of half-cells assembled using three-dimensional(3D)porous copper foil(PCu)and copper as current collector is better than that of Al foil,which stabilizes at 138.2 and 132.8 mAh·g^(-1)after 100 cycles at 0.05 A·g^(-1).The potassium-ion capacitor assembled using PCu exhibits an excellent energy/power density of 86.1 Wh·kg^(-1)and 4000 W·kg^(-1),respectively.This work will boost the rational design and provide an effective strategy to improve the performance of potassium-ion capacitors.
文摘Objective For the inverters used in UPS, it is important to maintain the pure sinusoidal AC output voltage waveform over all loading conditions and transients. Methods A novel sinusoidal output voltage control strategy is pregented in this paper. The output voltage is controlled by introducing filtering eapacitor current feedback. Two simple PI regulators are used for the current and voltage control loops. Results With the new control strategy, the inverter achieves very low output voltage distortion, good output voltage regulation and strong perturbation rejection, fast dynamic response, and good performance under nonlinear loads. The THD under capacitance rectifying load is better than 0.2%, the output voltage regulation within 0 to full load is less than 0.1%. The resting time under load transient is within 200?μ s . Conclusion The merits of the new control strategy include rapid response and good steady state stiffness.
文摘To miniaturize a very low level dc current amplifier and to improve its output response speed, the switched capacitor negative feedback circuit (SCNF), instead of the conventionally used high-ohmage resistor, is presented in this paper. In our system, a switched capacitor filter (SCF) and an offset controller are also used to decrease vibrations and offset voltage at the output of the amplifier using SCNF. The theoretical output voltage of the very low level dc current amplifier using SCNF is obtained. The experimental results show that the unnecessary components of the amplifier’s output are much decreased, and that the response speed of the amplifier with both the SCNF and SCF is faster than that using high-ohmage resistor.
文摘In this paper,an interleaved LCLC converter with enhancement-mode(E-mode)GaN devices is introduced to achieve the accurate current sharing performance for data center applications. Any tolerance in the resonant tank elements can lead to large load imbalance between any two different phases. Due to the steep gain curves of LCLC converters,conventional current sharing methods are not effective. In the proposed converter,the impedances of the resonant networks are matched by switching a capacitor,i.e.,switch controlled capacitor(SCC),in series with the resonant capacitor in one or some of the phases,which results in accurate load current sharing among the phases with an accuracy around 0.025%. The load share of a phase is sensed through the resonant current on it,and the control logic applied to such current sharing can be achieved. By this method,accurate current sharing is achieved for a wide input voltage range required for the hold-up time in data center applications. Interleaving is applied in the proposed multiphase LCLC converter,resulting in low current stress on the output capacitor and allowing ceramic capacitor implementation. Moreover,phase shedding accomplishes high light load efficiency. The performance of the proposed interleaved LCLC converter is verified by a two-phase 1 k W prototype with an input voltage ranging from 250 V to 400 V and a fixed 12 V output voltage.
基金supported by the National Natural Science Foundation of China(Grant No.22075064)National Key Laboratory Projects(No.SYSKT20230056).
文摘Supercapacitors,comprising electrical double-layer capacitors(EDLCs)and pseudocapa-citors,are widely acknowledged as high-power energy storage devices.However,their local structures and fundamental mechanisms remain poorly understood,and suitable experimental techniques for investigation are also lacking.Recently,nuclear magnetic resonance(NMR)has emerged as a powerful tool for addressing these fundamental issues with high local sensitivity and non-invasiveness.In this paper,we first review the limi-tations of existing characterization methods and highlight the advantages of NMR in investigating mechanisms of supercapacitors.Subsequently,we introduce the basic prin-ciple of ring current effect,NMR-active nuclei,and various NMR techniques employed in exploring energy storage mechanisms including cross polarization(CP)magic angle spinning(MAS)NMR,multiple-quantum(MQ)MAS,two-dimensional exchange spec-troscopy(2D-EXSY)NMR,magnetic resonance imaging(MRI)and pulsed-field gradient(PFG)NMR.Based on this,recent progress in investigating energy storage mechanisms in EDLCs and pseudocapacitors through various NMR techniques is discussed.Finally,an outlook on future directions for NMR research in supercapacitors is offered.
基金This study was financially supported by Beijing Education Commission,China.
文摘Growth and passivation of tunnels within Al foil by on-off controlling DC etching in 6 wt.% HCI solution has been investigated. It was found that, in a given etchant solution at a special temperature, the longest tunnel length was only a function of the turn-on interval of DC. The potential of Al foil broke at on-off controlling DC by the result from anode polarization curves and potential-time （E-t） responding curves. When DC was switched on, the potential increased abruptly over pitting potential, leading to nucleation of pits at the surface and the growth of tunnels at special length. When DC was switched off, the potential decreased rapidly to a passive value, leading to stoppage of nucleation and death of tunnels. By this way, the longest tunnel length can be controlled and a non-piercing layer can be obtained. Hence, etching of Al foil at this current is beneficial for maintaining a good mechanical strength.
基金supported in part by the Jiangsu Natural Science Foundation of China under Grant BK20180013in part by the Shenzhen Science and Technology Innovation Committee(STIC)under Grant JCYJ20180306174439784.
文摘The pulse-width-modulated(PWM)current-source converters(CSCs)fed electric machine systems can be considered as a type of high reliability energy conversion systems,since they work with the long-life DC-link inductor and offer high fault-tolerant capability for short-circuit faults.Besides,they provide motor friendly waveforms and four-quadrant operation ability.Therefore,they are suitable for high-power applications of fans,pumps,compressors and wind power generation.The purpose of this paper is to comprehensively review recent developments of key technologies on modulation and control of high-power(HP)PWM-CSC fed electric machines systems,including reduction of low-order current harmonics,suppression of inductor–capacitor(LC)resonance,mitigation of common-mode voltage(CMV)and control of modular PWM-CSC fed systems.In particular,recent work on the overlapping effects during commutation,LC resonance suppression under fault-tolerant operation and collaboration of modular PMW-CSCs are described.Both theoretical analysis and some results in simulations and experiments are presented.Finally,a brief discussion regarding the future trend of the HP CSC fed electric machines systems is presented.
基金National Natural Science Foundation of China(No.61741508)
文摘Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability reduction.In order to solve these problems,a finite control set model predictive control(FCS-MPC)for FSTP AC-DC converters with DC-link capacitor voltage balancing is proposed.In this strategy,in order to facilitate calculation,theαβcoordinate system model is established and all voltage vectors are evaluated by establishing a cost function.During the whole process,phase locked loop(PLL)and complex modulation strategy are not required.In the new established cost function,the additional objective term of suppressing capacitor voltage fluctuation is to eliminate effectively the capacitor voltages oscillations and deviations and improve the system reliability.The simulation results show that the proposed strategy can keep the capacitor voltage balancing and has good dynamic and static performance.
基金Project supported by the National Natural Science Foundation of China （Grant No 60376019）.
文摘The paper reports that Hfrio dielectric is deposited by reactive co-sputtering of Hf and Ti targets in an Ar/O2 ambience, followed by an annealing in different gas ambiences of N2, NO and NH3 at 600℃ for 2 min. Capacitancevoltage and gate-leakage properties are characterized and compared. The results indicate that the NO-annealed sample exhibits the lowest interface-state and dielectric-charge densities and best device reliability. This is attributed to the fact that nitridation can create strong Si≡N bonds to passivate dangling Si bonds and replace strained Si-O bonds, thus the sample forms a hardened dielectric/Si interface with high reliability.
