By virtue of alternating direction method of multipliers(ADMM), Newton-Raphson method, ratio consensus approach and running sum method, two distributed iterative strategies are presented in this paper to address the e...By virtue of alternating direction method of multipliers(ADMM), Newton-Raphson method, ratio consensus approach and running sum method, two distributed iterative strategies are presented in this paper to address the economic dispatch problem(EDP) in power systems. Different from most of the existing distributed ED approaches which neglect the effects of packet drops or/and time delays, this paper takes into account both packet drops and time delays which frequently occur in communication networks. Moreover, directed and possibly unbalanced graphs are considered in our algorithms, over which many distributed approaches fail to converge. Furthermore, the proposed schemes can address the EDP with local constraints of generators and nonquadratic convex cost functions, not just quadratic ones required in some existing ED approaches. Both theoretical analyses and simulation studies are provided to demonstrate the effectiveness of the proposed schemes.展开更多
Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a signifi...Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a significant issue.However,the traditional calculation methods aiming at synchronous generators cannot be directly applied to the DFIG wind turbines.A new method is needed to calculate the short-circuit current required by the planning,protection and control of the power grid.The short-circuit transition of DFIG under symmetrical and asymmetric short-circuit conditions are mathematically deduced,and the short-circuit characteristics of DFIG are analyzed.A new method is proposed to calculate the steady-state short-circuit current of DFIG based on the derived expressions.The time-domain simulations are conducted to verify the accuracy of the proposed method.展开更多
Magnetic radiation phenomena appear inevitably in the magnetic-resonance wireless power transfer (MR-WPT) system, and regarding this problem the magnetic-shielding scheme is applied to improve the electromagnetic pe...Magnetic radiation phenomena appear inevitably in the magnetic-resonance wireless power transfer (MR-WPT) system, and regarding this problem the magnetic-shielding scheme is applied to improve the electromagnetic performance in engineering. In this study, the shielding effectiveness of a two-coil MR-WPT system for different material shields is analyzed in theory using Moser's formula and Schelkunoff's formula. On this basis a candidate magnetic-shielding scheme with a double-layer structure is determined, which has better shielding effectiveness and coils coupling coefficient. Finally, some finite element simulation results validate the correctness of the theoretical analysis, and the shielding effectiveness with the double-layer shield in maximum is 30?dB larger than the one with the single-layer case.展开更多
Recently,poly(ethylene oxide)(PEO)-based solid polymer electrolytes have been attracting great attention,and efforts are currently underway to develop PEO-based composite electrolytes for next generation high performa...Recently,poly(ethylene oxide)(PEO)-based solid polymer electrolytes have been attracting great attention,and efforts are currently underway to develop PEO-based composite electrolytes for next generation high performance all-solid-state lithium metal batteries.In this article,a novel sandwich structured solid-state PEO composite electrolyte is developed for high performance all-solid-state lithium metal batteries.The PEO-based composite electrolyte is fabricated by hot-pressing PEO,LiTFSI and Ti_(3)C_(2)T_(x) MXene nanosheets into glass fiber cloth(GFC).The as-prepared GFC@PEO-MXene electrolyte shows high mechanical properties,good electrochemical stability,and high lithium-ion migration number,which indicates an obvious synergistic effect from the microscale GFC and the nanoscale MXene.Such as,the GFC@PEO-1 wt%MXene electrolyte shows a high tensile strength of 43.43 MPa and an impressive Young's modulus of 496 MPa,which are increased by 1205%and 6048%over those of PEO.Meanwhile,the ionic conductivity of GFC@PEO-1 wt%MXene at 60℃ reaches 5.01×10^(-2) S m^(-1),which is increased by around 200%compared with that of GFC@PEO electrolyte.In addition,the Li/Li symmetric battery based on GFC@PEO-1 wt%MXene electrolyte shows an excellent cycling stability over 800 h(0.3 mA cm^(-2),0.3 mAh cm^(-2)),which is obviously longer than that based on PEO and GFC@PEO electrolytes due to the better compatibility of GFC@PEO-1 wt%MXene electrolyte with Li anode.Furthermore,the solid-state Li/LiFePO_(4) battery with GFC@PEO-1 wt%MXene as electrolyte demonstrates a high capacity of 110.2–166.1 mAh g^(-1) in a wide temperature range of 25–60C,and an excellent capacity retention rate.The developed sandwich structured GFC@PEO-1 wt%MXene electrolyte with the excellent overall performance is promising for next generation high performance all-solid-state lithium metal batteries.展开更多
With the trend of multiple energies or flexible demand in power systems,binary variables appear in systemwide constraints,which are the foundation of marginal pricing currently in markets.An appropriate pricing method...With the trend of multiple energies or flexible demand in power systems,binary variables appear in systemwide constraints,which are the foundation of marginal pricing currently in markets.An appropriate pricing method incentivizes compliance of market participants;otherwise,compliance can be incentivized by paying discriminatory uplift payments which jeopardize transparency of markets.This paper proposes two theorems to examine whether the binary variables brought by multiple energies and flexible demand will impact compliance under marginal pricing.The first theorem shows sufficient conditions with which marginal pricing with fixed binary variables incentivizes compliance,while the second theorem shows sufficient conditions to require uplift payments.To improve transparency by reducing uplift payments under cases which fall into the second theorem,this paper further proposes a pricing method by combining 1)designed constraints to price binary variables in system-wide constraints,and 2)convex hull pricing to price binary variables in private constraints.Effectiveness of the proposed theorems and pricing method is verified in an electricity-gas case(consisting of the IEEE 30-bus system and the NGS 10-node system)and the IEEE 118-bus test system.展开更多
Wind energy is one of the most promising and renewable energy sources;however,owing to the limitations of device structures,collecting low-speed wind energy by triboelectric nanogenerators(TENGs)is still a huge challe...Wind energy is one of the most promising and renewable energy sources;however,owing to the limitations of device structures,collecting low-speed wind energy by triboelectric nanogenerators(TENGs)is still a huge challenge.To solve this problem,an ultra-durable and highly efficient windmill-like hybrid nanogenerator(W-HNG)is developed.Herein,the W-HNG composes coupled TENG and electromagnetic generator(EMG)and adopts a rotational contact-separation mode.This unique design efficiently avoids the wear of friction materials and ensures a prolonged service life.Moreover,the generator group is separated from the wind-driven part,which successfully prevents rotation resistance induced by the friction between rotor and stator in the conventional structures,and realizes low-speed wind energy harvesting.Additionally,the output characteristics of TENG can be complementary to the different performance advantages of EMG to achieve a satisfactory power production.The device is successfully driven when the wind speed is 1.8 m s−1,and the output power of TENG and EMG can achieve 0.95 and 3.7 mW,respectively.After power management,the W-HNG has been successfully applied as a power source for electronic devices.This work provides a simple,reliable,and durable device for improved performance toward large-scale low-speed breeze energy harvesting.展开更多
Cattle encephalon glycoside and ignotin(CEGI)injection is known as a multi-target neuroprotective drug that contains numerous liposoluble molecules,such as polypeptides,monosialotetrahexosyl ganglioside(GM-1),free ami...Cattle encephalon glycoside and ignotin(CEGI)injection is known as a multi-target neuroprotective drug that contains numerous liposoluble molecules,such as polypeptides,monosialotetrahexosyl ganglioside(GM-1),free amino acids,hypoxanthine and carnosine.CEGI has been approved by the Chinese State Food and Drug Administration and widely used in the treatments of various diseases,such as stroke and Alzheimer's disease.However,the neuroprotective effects of CEGI beyond the time window of thrombolysis(within 4.5 hours)on acute ischemic stroke remain unclear.This study constructed a rat middle cerebral artery occlusion model by suture-occluded method to simulate ischemic stroke.The first daily dose was intraperitoneally injected at 8 hours post-surgery and the CEGI treatments continued for 14 days.Results of the modified five-point Bederson scale,beam balance test and rotameric test showed the neurological function of ischemic stroke rats treated with 4 m L/kg/d CEGI improved significantly,but the mortality within 14 days did not change significantly.Brain MRI and 2,3,5-triphenyltetrazolium chloride staining confirmed that the infarct size in the 4 m L/kg/d CEGI-treated rats was significantly reduced compared with ischemic insult only.The results of transmission electron microscopy and double immunofluorescence staining showed that the hippocampal neuronal necrosis in the ischemic penumbra decreased whereas the immunopositivity of new neuronal-specific protein doublecortin and the percentage of Ki67/doublecortin positive cells increased in CEGI-treated rats compared with untreated rats.Our results suggest that CEGI has an effective neuroprotective effect on ischemic stroke when administered after the time window of thrombolysis.The study was approved by the Animal Ethics Committee of The Third Military Medical University,China.展开更多
An adaptive fast multipole higher order boundary element method combining fast multipole (FM) with a higher order boundary element method is studied to solve the power frequency electric field (PFEF) of substation...An adaptive fast multipole higher order boundary element method combining fast multipole (FM) with a higher order boundary element method is studied to solve the power frequency electric field (PFEF) of substations. In this new technique, the iterative equation solver GMRES is used in the FM, where matrix-vector multiplications are calculated using fast multipole expansions. The coefficients in the preconditioner for GMRES are stored and are used repeatedly in the direct evaluations of the near-field contributions. Then a 500kV outdoor substation is modeled and the PFEF of the substation is analyzed by the novel algorithm and other conventional methods. The results show that, in computational cost and the storages capability aspects, the algorithm proposed in this study has obvious advantages. It is suitable for the calculation of the large-scale PFEF in complex substations and the design of electromagnetic compatibility.展开更多
The large application of renewable energy generation(REG)has increased the risk of cascading failures in the power system.At the same time REG also provides the possibility of new approaches for the suppression of suc...The large application of renewable energy generation(REG)has increased the risk of cascading failures in the power system.At the same time REG also provides the possibility of new approaches for the suppression of such failures.However,the capacity and position of the synchronous generator(SG)involved in regulation limit the power regu-lation speed(PRS)of REG to the overload line which is the main cause of cascading failures,while the PRS of SG is related to the position and shedding power.REG and SGs have difficulty in achieving effective cooperation under constraints of system power balance.Particularly,the dynamic variation of line flow during power regulation causes new problems for the accurate evaluation of line thermal safety under overload.Therefore,a new strategy for quan-titatively coordinating shedding power and power regulation to block cascading failures in the dynamic security domain is proposed in this paper.The control capability and dynamic security domain of the overload line are mod-eled,and the coordination control method based on power regulation is then proposed to minimize shedding power.The algorithm for the optimal control scheme considers the constraints of load capacity,power source capacity and bus PRS.The correctness of the proposed method is verified using case studies.展开更多
A bulk power system is conventionally characterized by a complex structure with a large number of components. Each component generally has a different contribution to the transmission congestion(TC) of a system. Thus,...A bulk power system is conventionally characterized by a complex structure with a large number of components. Each component generally has a different contribution to the transmission congestion(TC) of a system. Thus, a TC sharing method that can be used to evaluate the contribution of each component to the system TC and recognize the weak parts from the perspective of TC should be built. This paper presents a transmission congestion tracing(TCT) principle based on the failed component sharing principle and proportional sharing principle and a TCT model using the Monte Carlo simulation method. Case studies on the IEEE Reliability Test System indicate that the proposed method is effective and feasible.展开更多
Wind power converter(WPC)is a key part of a wind power unit which delivers electric energy to power grid.Because of a large number of semiconductors,WPC has a high failure rate.This paper proposes a method to accurate...Wind power converter(WPC)is a key part of a wind power unit which delivers electric energy to power grid.Because of a large number of semiconductors,WPC has a high failure rate.This paper proposes a method to accurately evaluate the reliability of WPC,which is crucial for the design and maintenance of wind turbines.Firstly,the index of effective temperature(ET)is presented to quantify the effects of temperature and humidity on the semiconductor operation.A novel method is proposed to evaluate the lifetime and calculate the aging failure rates of the semiconductors considering the fluctuations of ET.Secondly,the failure mode and effect analysis(FMEA)of WPC is investigated based on the topology and control scheme.The conventional two-state reliability model of the WPC is extended to the multi-state reliability model where the partial working state under the fault-tolerant control scheme is allowed.Finally,a reliability evaluation framework is established to calculate the parameters of the WPC reliability model considering the variable failure rates and repair activities of semiconductors.Case studies are designed to verfify the proposed method using a practical wind turbine.展开更多
The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-seq...The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of syn-chronous generators.Based on the model,the synchronization characteristics of the VSC system under asymmetric grid faults are described,and the interaction mechanisms,as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained.Using the equal area criterion,the influences of sequence control switching action,detection delay,and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed,respectively.In addition,a transient stabil-ity assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed.Finally,the analytical results are validated through simulation and experiments.展开更多
In northern China,thermal power units(TPUs)are important in improving the penetration level of renewable energy.In such areas,the potentials of coordinated dispatch of renewable energy sources(RESs)and TPUs can be bet...In northern China,thermal power units(TPUs)are important in improving the penetration level of renewable energy.In such areas,the potentials of coordinated dispatch of renewable energy sources(RESs)and TPUs can be better realized,if RESs and TPUs connected to the power grid at the same point of common coupling(PCC)are dispatched as a coupled system.Firstly,the definition of the coupled system is introduced,followed by an analysis on its characteristics.Secondly,based on the operation characteristics of deep peak regulation(DPR)of TPUs in the coupled system,the constraint of the ladder-type ramping rate applicable for day-ahead dispatch is proposed,and the corresponding flexible spinning reserve constraint is further established.Then,considering these constraints and peak regulation ancillary services,a day-ahead optimal dispatch model of the coupled system is established.Finally,the operational characteristics and advantages of the coupled system are analyzed in several case studies based on a real-world power grid in Liaoning province,China.The numerical results show that the coupled system can further improve the economic benefits of RESs and TPUs under the existing policies.展开更多
Efficient nitrogen fixation through a reactive plasma process attracts intense interest due to the environmental issues induced by the conventional Haber–Bosch method. In this work, we present a direct and simple fix...Efficient nitrogen fixation through a reactive plasma process attracts intense interest due to the environmental issues induced by the conventional Haber–Bosch method. In this work, we present a direct and simple fixation routine without any catalysts for nitrogen in open air using an atmospheric-pressure pin-to-solution plasma electrolytic system. Nitrate, nitrite, and ammonia as the nitrogen-derived chemicals in solution were analyzed as indicators under various discharge conditions to estimate the energy efficiency of this process. The results show that the nitrogen fixation process was much more efficient by the pin-positive discharge compared to the negative one. N chemicals preferred to be formed when the solution was of negative polarity. It was also found that, with the help of solution circulation, the energy efficiency was enhanced compared to that of static liquid. However, an inverse trend was observed with the increase of the discharge current. Further study by optical emission spectroscopy indicates the important roles of active N2* and water vapour and their derived species near the plasma–water interface in the fixation process.展开更多
Triboelectric nanogenerator(TENG)is regarded as an effective strategy to convert environment mechanical energy into electricity to meet the distributed energy demand of large number of sensors in the Internet of Thing...Triboelectric nanogenerator(TENG)is regarded as an effective strategy to convert environment mechanical energy into electricity to meet the distributed energy demand of large number of sensors in the Internet of Things(IoTs).Although TENG based on the coupling of triboelectrification and air-breakdown achieves a large direct current(DC)output,material abrasion is a bottleneck for its applications.Here,inspired by primary cell and its DC signal output characteristics,we propose a novel primary cell structure TENG(PC-TENG)based on contact electrification and electrostatic induction,which has multiple working modes,including contact separation mode,freestanding mode and rotation mode.The PC-TENG produces DC output and operates at low surface contact force.It has an ideal effective charge density(1.02 m Cm^(-2)).Meanwhile,the PC-TENG shows a superior durability with 99% initial output after 100,000 operating cycles.Due to its excellent output performance and durability,a variety of commercial electronic devices are powered by PC-TENG via harvesting wind energy.This work offers a facile and ideal scheme for enhancing the electrical output performance of DC-TENG at low surface contact force and shows a great potential for the energy harvesting applications in IoTs.展开更多
Better electrical insulation and thermal management are both urgently required in integrated power semiconductors.Electrical insulation epoxy encapsulation suffers from poor heat conduction,which has increasingly beco...Better electrical insulation and thermal management are both urgently required in integrated power semiconductors.Electrical insulation epoxy encapsulation suffers from poor heat conduction,which has increasingly become a bottleneck of power semiconductors integration.Although incorporating high thermal conductivity ceramics,such as hexagonal boron nitride(hBN),aluminium nitride etc.into epoxy promotes the thermal conductivity,the eco-friendly scalable fabrication of these composites with sufficient electrical breakdown strength remains a formidable challenge.Suitable voltage stabilizers are known to provide additional benefits to breakdown strength.Herein,a highthroughput approach combining plasma with roll-to-roll was developed.The voltage stabilizer(acetophenone)was grafted on interfaces between hBN and epoxy matrix through plasma.The high-energy electrons are consumed by the grafted interface,which leads to the significant suppression of partial discharge in Epoxy/hBN.Meanwhile,interfacial phonon scattering is repaired by grafting.Therefore,the epoxy composite concurrently exhibits improved breakdown strength(by 27.4%)and thermal conductivity(by 142.9%)at about 11.9 wt.%filler content,outperforming the pure epoxy.Consequently,a promising modification strategy for mass production is provided for the encapsulation materials in various high-power-density semiconductor devices.展开更多
All-solid-state switches are one of the core components of pulsed power supply systems.However,the voltage level of a single switch is limited.By optimizing the chip structure,the voltage level of a single switch can ...All-solid-state switches are one of the core components of pulsed power supply systems.However,the voltage level of a single switch is limited.By optimizing the chip structure,the voltage level of a single switch can be improved.Due to the immaturity of the production process and the positive correlation between the blocking voltage and the onresistance of the switch,it is difficult to improve the blocking voltage and the continuous forward current of a single switch simultaneously.The series-connected switch is a way to increase the switch's blocking voltage without reducing the switch's continuous forward current.Magnetically coupled isolated drive and resistor-capacitor forced voltage equalization techniques are investigated to increase the blocking voltage of the switches using multiple SiC metal-oxide-semiconductor field-effect transistors(MOSFETs)in series connections.Meanwhile,a special overcurrent protection scheme is designed to improve the reliability of the series-connected switch.Finally,a high-voltage solid-state switch is developed based on the SiC MOSFET series connections,whose output pulse width is adjustable from 20 to 300μs,frequency is adjustable from 1 Hz to 3 kHz,the maximum output voltage can reach 57 kV(1 Hz),and the overcurrent protection time is about 1μs.展开更多
The surface-enhanced Raman scattering(SERS)substrates enable a highly sensitive detection of furfural in the transformer oil.However,detection substrates with long-term stability are still extremely challenging.In thi...The surface-enhanced Raman scattering(SERS)substrates enable a highly sensitive detection of furfural in the transformer oil.However,detection substrates with long-term stability are still extremely challenging.In this work,we anchored the thiol-containing coupling agents 2,5-dimercapto-1,3,4-thiadiazole(DMTD)and 1,4-benzenedithiol(BDT)on the surface of bubble copper(B-Cu)and flower-like silver nanoparticles(FAg),respectively.The three-dimensional SERS detection substrates with long-term stability by using a combination of chemical reduction and self-assembly methods were constructed.The substrate has a minimum detection limit of 10^(−9) M for rhodamine B in oil with an enhancement factor of up to 2.23×10^(7).Importantly,the three-crystal BCu@F-Ag_(1)@Au_(5) substrate was used for the detection of furfural in the transformer oil with a detection limit of 2 mg/L and a relative standard deviation value of 2.46%.After 60 days of a simulated operation,the detection signal of furfural in the transformer oil samples at 75℃ and still reached the initial value of 77.53%,indicating that the substrate has a good long-term stability.This triple frame structured SERS detection platform shows great potential in tracking furfural in the aging transformer oil mixing systems.展开更多
基金supported by the National Natural Science Foundation of China(61673077)。
文摘By virtue of alternating direction method of multipliers(ADMM), Newton-Raphson method, ratio consensus approach and running sum method, two distributed iterative strategies are presented in this paper to address the economic dispatch problem(EDP) in power systems. Different from most of the existing distributed ED approaches which neglect the effects of packet drops or/and time delays, this paper takes into account both packet drops and time delays which frequently occur in communication networks. Moreover, directed and possibly unbalanced graphs are considered in our algorithms, over which many distributed approaches fail to converge. Furthermore, the proposed schemes can address the EDP with local constraints of generators and nonquadratic convex cost functions, not just quadratic ones required in some existing ED approaches. Both theoretical analyses and simulation studies are provided to demonstrate the effectiveness of the proposed schemes.
基金supported by State Key Laboratory of Power Transmission Equipment and System Security(No.2007DA10512711102,No.2007DA10512709202)Program of Introducing Talents of Discipline to Universities("111"Program)(No.B08036)the Fundamental Research Funds for the Central Universities(No.CDJXS11150026)
文摘Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a significant issue.However,the traditional calculation methods aiming at synchronous generators cannot be directly applied to the DFIG wind turbines.A new method is needed to calculate the short-circuit current required by the planning,protection and control of the power grid.The short-circuit transition of DFIG under symmetrical and asymmetric short-circuit conditions are mathematically deduced,and the short-circuit characteristics of DFIG are analyzed.A new method is proposed to calculate the steady-state short-circuit current of DFIG based on the derived expressions.The time-domain simulations are conducted to verify the accuracy of the proposed method.
基金Supported by the National Natural Science Foundation of China under Grant No 51377185
文摘Magnetic radiation phenomena appear inevitably in the magnetic-resonance wireless power transfer (MR-WPT) system, and regarding this problem the magnetic-shielding scheme is applied to improve the electromagnetic performance in engineering. In this study, the shielding effectiveness of a two-coil MR-WPT system for different material shields is analyzed in theory using Moser's formula and Schelkunoff's formula. On this basis a candidate magnetic-shielding scheme with a double-layer structure is determined, which has better shielding effectiveness and coils coupling coefficient. Finally, some finite element simulation results validate the correctness of the theoretical analysis, and the shielding effectiveness with the double-layer shield in maximum is 30?dB larger than the one with the single-layer case.
基金support of the Fundamental Research Funds for the Central Universities(No.2022CDJQY-004)the Fund for Innovative Research Groups of Natural Science Foundation of Hebei Province(No.A2020202002).
文摘Recently,poly(ethylene oxide)(PEO)-based solid polymer electrolytes have been attracting great attention,and efforts are currently underway to develop PEO-based composite electrolytes for next generation high performance all-solid-state lithium metal batteries.In this article,a novel sandwich structured solid-state PEO composite electrolyte is developed for high performance all-solid-state lithium metal batteries.The PEO-based composite electrolyte is fabricated by hot-pressing PEO,LiTFSI and Ti_(3)C_(2)T_(x) MXene nanosheets into glass fiber cloth(GFC).The as-prepared GFC@PEO-MXene electrolyte shows high mechanical properties,good electrochemical stability,and high lithium-ion migration number,which indicates an obvious synergistic effect from the microscale GFC and the nanoscale MXene.Such as,the GFC@PEO-1 wt%MXene electrolyte shows a high tensile strength of 43.43 MPa and an impressive Young's modulus of 496 MPa,which are increased by 1205%and 6048%over those of PEO.Meanwhile,the ionic conductivity of GFC@PEO-1 wt%MXene at 60℃ reaches 5.01×10^(-2) S m^(-1),which is increased by around 200%compared with that of GFC@PEO electrolyte.In addition,the Li/Li symmetric battery based on GFC@PEO-1 wt%MXene electrolyte shows an excellent cycling stability over 800 h(0.3 mA cm^(-2),0.3 mAh cm^(-2)),which is obviously longer than that based on PEO and GFC@PEO electrolytes due to the better compatibility of GFC@PEO-1 wt%MXene electrolyte with Li anode.Furthermore,the solid-state Li/LiFePO_(4) battery with GFC@PEO-1 wt%MXene as electrolyte demonstrates a high capacity of 110.2–166.1 mAh g^(-1) in a wide temperature range of 25–60C,and an excellent capacity retention rate.The developed sandwich structured GFC@PEO-1 wt%MXene electrolyte with the excellent overall performance is promising for next generation high performance all-solid-state lithium metal batteries.
基金supported by the National Natural Science Foundation of China(52177072).
文摘With the trend of multiple energies or flexible demand in power systems,binary variables appear in systemwide constraints,which are the foundation of marginal pricing currently in markets.An appropriate pricing method incentivizes compliance of market participants;otherwise,compliance can be incentivized by paying discriminatory uplift payments which jeopardize transparency of markets.This paper proposes two theorems to examine whether the binary variables brought by multiple energies and flexible demand will impact compliance under marginal pricing.The first theorem shows sufficient conditions with which marginal pricing with fixed binary variables incentivizes compliance,while the second theorem shows sufficient conditions to require uplift payments.To improve transparency by reducing uplift payments under cases which fall into the second theorem,this paper further proposes a pricing method by combining 1)designed constraints to price binary variables in system-wide constraints,and 2)convex hull pricing to price binary variables in private constraints.Effectiveness of the proposed theorems and pricing method is verified in an electricity-gas case(consisting of the IEEE 30-bus system and the NGS 10-node system)and the IEEE 118-bus test system.
基金The authors gratefully acknowledge the financial support from the Natural Science Foundation of Chongqing(Grant No.cstc2017jcyjAX0307)the Fundamental Research Funds for the Central Universities(Grant Nos.CYFH201821,2020CDCGJ005,2018CDQYWL0046,2019CDXZWL001)the National Natural Science Foundation of China(Grant No.51402112).
文摘Wind energy is one of the most promising and renewable energy sources;however,owing to the limitations of device structures,collecting low-speed wind energy by triboelectric nanogenerators(TENGs)is still a huge challenge.To solve this problem,an ultra-durable and highly efficient windmill-like hybrid nanogenerator(W-HNG)is developed.Herein,the W-HNG composes coupled TENG and electromagnetic generator(EMG)and adopts a rotational contact-separation mode.This unique design efficiently avoids the wear of friction materials and ensures a prolonged service life.Moreover,the generator group is separated from the wind-driven part,which successfully prevents rotation resistance induced by the friction between rotor and stator in the conventional structures,and realizes low-speed wind energy harvesting.Additionally,the output characteristics of TENG can be complementary to the different performance advantages of EMG to achieve a satisfactory power production.The device is successfully driven when the wind speed is 1.8 m s−1,and the output power of TENG and EMG can achieve 0.95 and 3.7 mW,respectively.After power management,the W-HNG has been successfully applied as a power source for electronic devices.This work provides a simple,reliable,and durable device for improved performance toward large-scale low-speed breeze energy harvesting.
基金the 63rd Batch of First-Class Financing for Chinese Postdoctoral Science Foundation,No.2018M631061(to LT)Macao Youth Scholars Program,No.AM201918(to LT)。
文摘Cattle encephalon glycoside and ignotin(CEGI)injection is known as a multi-target neuroprotective drug that contains numerous liposoluble molecules,such as polypeptides,monosialotetrahexosyl ganglioside(GM-1),free amino acids,hypoxanthine and carnosine.CEGI has been approved by the Chinese State Food and Drug Administration and widely used in the treatments of various diseases,such as stroke and Alzheimer's disease.However,the neuroprotective effects of CEGI beyond the time window of thrombolysis(within 4.5 hours)on acute ischemic stroke remain unclear.This study constructed a rat middle cerebral artery occlusion model by suture-occluded method to simulate ischemic stroke.The first daily dose was intraperitoneally injected at 8 hours post-surgery and the CEGI treatments continued for 14 days.Results of the modified five-point Bederson scale,beam balance test and rotameric test showed the neurological function of ischemic stroke rats treated with 4 m L/kg/d CEGI improved significantly,but the mortality within 14 days did not change significantly.Brain MRI and 2,3,5-triphenyltetrazolium chloride staining confirmed that the infarct size in the 4 m L/kg/d CEGI-treated rats was significantly reduced compared with ischemic insult only.The results of transmission electron microscopy and double immunofluorescence staining showed that the hippocampal neuronal necrosis in the ischemic penumbra decreased whereas the immunopositivity of new neuronal-specific protein doublecortin and the percentage of Ki67/doublecortin positive cells increased in CEGI-treated rats compared with untreated rats.Our results suggest that CEGI has an effective neuroprotective effect on ischemic stroke when administered after the time window of thrombolysis.The study was approved by the Animal Ethics Committee of The Third Military Medical University,China.
基金Supported by the National Natural Science Foundations of China under Grant No 50877082, the National Basic Research Program of China under Grant No 2009CB724506, and the Specialized Research Fund for State Key Laboratory of Power Transmission Equipment & System Security and New Technology under Grant No 2007DA10512708304.
文摘An adaptive fast multipole higher order boundary element method combining fast multipole (FM) with a higher order boundary element method is studied to solve the power frequency electric field (PFEF) of substations. In this new technique, the iterative equation solver GMRES is used in the FM, where matrix-vector multiplications are calculated using fast multipole expansions. The coefficients in the preconditioner for GMRES are stored and are used repeatedly in the direct evaluations of the near-field contributions. Then a 500kV outdoor substation is modeled and the PFEF of the substation is analyzed by the novel algorithm and other conventional methods. The results show that, in computational cost and the storages capability aspects, the algorithm proposed in this study has obvious advantages. It is suitable for the calculation of the large-scale PFEF in complex substations and the design of electromagnetic compatibility.
基金supported in part by the National Natural Science Foundation of China under Grant 51877018in part by the Natural Science Foundation of Chongqing under Grant cstc2019jcyj-msxmX0321in part by the Graduate Research and Innovation Foundation of Chongqing,China under Grant CYB22019.
文摘The large application of renewable energy generation(REG)has increased the risk of cascading failures in the power system.At the same time REG also provides the possibility of new approaches for the suppression of such failures.However,the capacity and position of the synchronous generator(SG)involved in regulation limit the power regu-lation speed(PRS)of REG to the overload line which is the main cause of cascading failures,while the PRS of SG is related to the position and shedding power.REG and SGs have difficulty in achieving effective cooperation under constraints of system power balance.Particularly,the dynamic variation of line flow during power regulation causes new problems for the accurate evaluation of line thermal safety under overload.Therefore,a new strategy for quan-titatively coordinating shedding power and power regulation to block cascading failures in the dynamic security domain is proposed in this paper.The control capability and dynamic security domain of the overload line are mod-eled,and the coordination control method based on power regulation is then proposed to minimize shedding power.The algorithm for the optimal control scheme considers the constraints of load capacity,power source capacity and bus PRS.The correctness of the proposed method is verified using case studies.
基金supported by National Natural Science Foundation of China(No.51247006)
文摘A bulk power system is conventionally characterized by a complex structure with a large number of components. Each component generally has a different contribution to the transmission congestion(TC) of a system. Thus, a TC sharing method that can be used to evaluate the contribution of each component to the system TC and recognize the weak parts from the perspective of TC should be built. This paper presents a transmission congestion tracing(TCT) principle based on the failed component sharing principle and proportional sharing principle and a TCT model using the Monte Carlo simulation method. Case studies on the IEEE Reliability Test System indicate that the proposed method is effective and feasible.
基金supported by the National Natural Science Foundation of China(No.52022016)China Postdoctoral Science Foundation(No.2021M693711)Fundamental Research Funds for the Central Universities(No.2021CDJQY-037)。
文摘Wind power converter(WPC)is a key part of a wind power unit which delivers electric energy to power grid.Because of a large number of semiconductors,WPC has a high failure rate.This paper proposes a method to accurately evaluate the reliability of WPC,which is crucial for the design and maintenance of wind turbines.Firstly,the index of effective temperature(ET)is presented to quantify the effects of temperature and humidity on the semiconductor operation.A novel method is proposed to evaluate the lifetime and calculate the aging failure rates of the semiconductors considering the fluctuations of ET.Secondly,the failure mode and effect analysis(FMEA)of WPC is investigated based on the topology and control scheme.The conventional two-state reliability model of the WPC is extended to the multi-state reliability model where the partial working state under the fault-tolerant control scheme is allowed.Finally,a reliability evaluation framework is established to calculate the parameters of the WPC reliability model considering the variable failure rates and repair activities of semiconductors.Case studies are designed to verfify the proposed method using a practical wind turbine.
基金supported in part by the National Natural Science Foundation of China under Grant 51977019in part by the Joint Research Fund in Smart Grid(U1966208)under cooperative agreement between the National Natural Science Foundation of China and State Grid Corporation of China.
文摘The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of syn-chronous generators.Based on the model,the synchronization characteristics of the VSC system under asymmetric grid faults are described,and the interaction mechanisms,as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained.Using the equal area criterion,the influences of sequence control switching action,detection delay,and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed,respectively.In addition,a transient stabil-ity assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed.Finally,the analytical results are validated through simulation and experiments.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50807058 and 50907076 and the Scientific Research Foundation of State Key Lab of Power Transmission Equipment and System Security (2007DA10512708205).
基金supported in part by the National Key Research and Development Program of China(No.2019YFB1505400).
文摘In northern China,thermal power units(TPUs)are important in improving the penetration level of renewable energy.In such areas,the potentials of coordinated dispatch of renewable energy sources(RESs)and TPUs can be better realized,if RESs and TPUs connected to the power grid at the same point of common coupling(PCC)are dispatched as a coupled system.Firstly,the definition of the coupled system is introduced,followed by an analysis on its characteristics.Secondly,based on the operation characteristics of deep peak regulation(DPR)of TPUs in the coupled system,the constraint of the ladder-type ramping rate applicable for day-ahead dispatch is proposed,and the corresponding flexible spinning reserve constraint is further established.Then,considering these constraints and peak regulation ancillary services,a day-ahead optimal dispatch model of the coupled system is established.Finally,the operational characteristics and advantages of the coupled system are analyzed in several case studies based on a real-world power grid in Liaoning province,China.The numerical results show that the coupled system can further improve the economic benefits of RESs and TPUs under the existing policies.
基金partly supported by National Natural Science Foundation of China (No. 11975061)the Technology Innovation and Application Development Project of Chongqing (No. cstc2019jscx-msxmX0041)+1 种基金the Construction Committee Project of Chongqing (No. 2018-1-3-6)the Fundamental Research Funds for the Central Universities (No. 2019CDQYDQ034)。
文摘Efficient nitrogen fixation through a reactive plasma process attracts intense interest due to the environmental issues induced by the conventional Haber–Bosch method. In this work, we present a direct and simple fixation routine without any catalysts for nitrogen in open air using an atmospheric-pressure pin-to-solution plasma electrolytic system. Nitrate, nitrite, and ammonia as the nitrogen-derived chemicals in solution were analyzed as indicators under various discharge conditions to estimate the energy efficiency of this process. The results show that the nitrogen fixation process was much more efficient by the pin-positive discharge compared to the negative one. N chemicals preferred to be formed when the solution was of negative polarity. It was also found that, with the help of solution circulation, the energy efficiency was enhanced compared to that of static liquid. However, an inverse trend was observed with the increase of the discharge current. Further study by optical emission spectroscopy indicates the important roles of active N2* and water vapour and their derived species near the plasma–water interface in the fixation process.
基金financially suppor ted by the National Key Research and Development Program(2018YFB2100100)the NSFC(U21A20147,52073037,62004017)。
文摘Triboelectric nanogenerator(TENG)is regarded as an effective strategy to convert environment mechanical energy into electricity to meet the distributed energy demand of large number of sensors in the Internet of Things(IoTs).Although TENG based on the coupling of triboelectrification and air-breakdown achieves a large direct current(DC)output,material abrasion is a bottleneck for its applications.Here,inspired by primary cell and its DC signal output characteristics,we propose a novel primary cell structure TENG(PC-TENG)based on contact electrification and electrostatic induction,which has multiple working modes,including contact separation mode,freestanding mode and rotation mode.The PC-TENG produces DC output and operates at low surface contact force.It has an ideal effective charge density(1.02 m Cm^(-2)).Meanwhile,the PC-TENG shows a superior durability with 99% initial output after 100,000 operating cycles.Due to its excellent output performance and durability,a variety of commercial electronic devices are powered by PC-TENG via harvesting wind energy.This work offers a facile and ideal scheme for enhancing the electrical output performance of DC-TENG at low surface contact force and shows a great potential for the energy harvesting applications in IoTs.
基金National Natural Science Foundation of China,Grant/Award Number:52277135Fund of the Key Laboratory of High Power Microwave Technology,Grant/Award Number:6142605190105Graduate Research and Innovation Foundation of Chongqing,Grant/Award Number:CYB22016。
文摘Better electrical insulation and thermal management are both urgently required in integrated power semiconductors.Electrical insulation epoxy encapsulation suffers from poor heat conduction,which has increasingly become a bottleneck of power semiconductors integration.Although incorporating high thermal conductivity ceramics,such as hexagonal boron nitride(hBN),aluminium nitride etc.into epoxy promotes the thermal conductivity,the eco-friendly scalable fabrication of these composites with sufficient electrical breakdown strength remains a formidable challenge.Suitable voltage stabilizers are known to provide additional benefits to breakdown strength.Herein,a highthroughput approach combining plasma with roll-to-roll was developed.The voltage stabilizer(acetophenone)was grafted on interfaces between hBN and epoxy matrix through plasma.The high-energy electrons are consumed by the grafted interface,which leads to the significant suppression of partial discharge in Epoxy/hBN.Meanwhile,interfacial phonon scattering is repaired by grafting.Therefore,the epoxy composite concurrently exhibits improved breakdown strength(by 27.4%)and thermal conductivity(by 142.9%)at about 11.9 wt.%filler content,outperforming the pure epoxy.Consequently,a promising modification strategy for mass production is provided for the encapsulation materials in various high-power-density semiconductor devices.
基金National Natural Science Foundation of China,Grant/Award Numbers:52277135,52237010The Graduate Student Research Innovation Project of Chongqing,Grant/Award Number:CYB22016。
文摘All-solid-state switches are one of the core components of pulsed power supply systems.However,the voltage level of a single switch is limited.By optimizing the chip structure,the voltage level of a single switch can be improved.Due to the immaturity of the production process and the positive correlation between the blocking voltage and the onresistance of the switch,it is difficult to improve the blocking voltage and the continuous forward current of a single switch simultaneously.The series-connected switch is a way to increase the switch's blocking voltage without reducing the switch's continuous forward current.Magnetically coupled isolated drive and resistor-capacitor forced voltage equalization techniques are investigated to increase the blocking voltage of the switches using multiple SiC metal-oxide-semiconductor field-effect transistors(MOSFETs)in series connections.Meanwhile,a special overcurrent protection scheme is designed to improve the reliability of the series-connected switch.Finally,a high-voltage solid-state switch is developed based on the SiC MOSFET series connections,whose output pulse width is adjustable from 20 to 300μs,frequency is adjustable from 1 Hz to 3 kHz,the maximum output voltage can reach 57 kV(1 Hz),and the overcurrent protection time is about 1μs.
基金National Natural Science Foundation of China,Grant/Award Number:51977017Chongqing Natural Science Foundation,Grant/Award Number:cstc2021jcyj-msxmX0617。
文摘The surface-enhanced Raman scattering(SERS)substrates enable a highly sensitive detection of furfural in the transformer oil.However,detection substrates with long-term stability are still extremely challenging.In this work,we anchored the thiol-containing coupling agents 2,5-dimercapto-1,3,4-thiadiazole(DMTD)and 1,4-benzenedithiol(BDT)on the surface of bubble copper(B-Cu)and flower-like silver nanoparticles(FAg),respectively.The three-dimensional SERS detection substrates with long-term stability by using a combination of chemical reduction and self-assembly methods were constructed.The substrate has a minimum detection limit of 10^(−9) M for rhodamine B in oil with an enhancement factor of up to 2.23×10^(7).Importantly,the three-crystal BCu@F-Ag_(1)@Au_(5) substrate was used for the detection of furfural in the transformer oil with a detection limit of 2 mg/L and a relative standard deviation value of 2.46%.After 60 days of a simulated operation,the detection signal of furfural in the transformer oil samples at 75℃ and still reached the initial value of 77.53%,indicating that the substrate has a good long-term stability.This triple frame structured SERS detection platform shows great potential in tracking furfural in the aging transformer oil mixing systems.