查看更多>>摘要：This paper presents a fully distributed state-of-charge balance control(DSBC)strategy for a distributed energy storage system(DESS).In this framework,each energy storage unit(ESU)processes the state-of-charge(SoC)information from its neighbors locally and adjusts the virtual impedance of the droop controller in real-time to change the current sharing.It is shown that the SoC balance of all ESUs can be achieved.Due to virtual impedance,voltage deviation of the bus occurs inevitably and increases with load power.Meanwhile,widespread of the constant power load(CPL)in the power system may cause instability.To ensure reliable operation of DESS under the proposed DSBC,the concept of the safe region is put forward.Within the safe region,DESS is stable and voltage deviation is acceptable.The boundary conditions of the safe region are derived from the equivalent model of DESS,in which stability is analyzed in terms of modified Brayton-Moser's criterion.Both simulations and hardware experiments verify the accuracy of the safe region and effectiveness of the proposed DSBC strategy.
查看更多>>摘要：In this paper,we propose a two-stage transmission hardening and planning(TH&P)model that can meet the load growth demand of normal scenarios and the resilience require-ments of hurricane-induced damage scenarios.To better measure the resilience requirements,the proposed TH&P model includes two resilience assessment indexes,namely,the load shedding(LS)under the damage scenario and the average connectivity degree(ACD)at different stages.The first-stage model,which aims to meet the load growth demand while minimizing the LS,is formulated as a mixed-integer linear program(MILP)to minimize the total planning and hardening cost of transmission lines,the operating cost of generators,and the penalty cost of wind power and load shedding in both normal and damage scenarios.The second-stage model aims to further improve the ACD when the ACD of the scheme obtained from the first-stage model cannot reach the target.Specifically,the contribution of each transmission line to the ACD is calculated,and the next hardened line is determined to increase the ACD.This process is repeated until the ACD meets the requirements.Case studies of the modified IEEE RTS-24 and two-area IEEE reliability test system-1996 indicate the proposed TH&P model can meet the requirements for both normal and damage scenarios.
查看更多>>摘要：How to effectively use the multi-energy demand elasticity of users to bid in the multi-energy market and formulate multi-energy retail packages is an urgent problem which needs to be solved by integrated energy service providers(IESPs)to attract more users and reduce operating costs.This paper presents a unified clearing of electricity and natural gas based on a bi-level bidding and multi-energy retail price formulation method for IESPs considering multi-energy demand elasticity.First,we propose an operating structure of IESPs in the wholesale and retail energy markets.The multi-energy demand elasticity model of retail-side users and a retail price model for electricity,gas,heat and cooling are established.Secondly,a bi-level bidding model for IESPs considering multi-energy demand elasticity is established to provide IESPs with wholesale-side bidding decisions and retail-side energy retail price decisions.Finally,an example is given to verify the proposed method.The results show that the method improves the total social welfare of the electricity and natural gas markets by 7.99％and the profit of IESPs by 1.40％.It can reduce the variance of the electricity,gas,and cooling load curves,especially the reduction of the variance of the electricity load curve can which reach 79.90％.It can be seen that the research in this paper has a positive effect on repairing the limitations of integrated energy trading research and improving the economics of the operation of IESPs.
查看更多>>摘要：In this paper,an island integrated energy system(IES)combining power,heat and hydrogen(CPHH)is built,and optimal power-heat-hydrogen scheduling is studied under actual plateau meteorological data.Considering the comprehen-sive demands of residents,an IES including renewable energy sources(RESs),fuel cell,electrolyzer,electric boiler,thermal energy storage device and new energy vehicles is established and operated.In the first stage of operation,according to the prediction of RESs and demands,day-ahead optimization is carried out which aims to minimize operation cost,while electric vehicles(EVs)are considered as special demand response(DR)loads.For the second stage of operation,ultra-short-term prediction is implemented to provide prediction data for model predictive control(MPC),realizing real-time operation.Functioning as a CPHH system,the fuel cell and electrolyzer collaborate to meet various needs of the plateau residential area with high efficiency.In addition,the method and IES structure proposed in this paper is compared with other options.
查看更多>>摘要：Composite insulators have been widely used in transmission lines.After being removed from transmission lines,their housing silicone material cannot degrade naturally.To tackle this problem,this paper proposes an effective method to recycle waste insulators by pyrolysis to obtain mullite(3A12O3·2SiO2)with high purity and compact structure.The recycling process studied will not generate toxic products.The thermal degradation process of housing material is investigated by analyzing its degradation products including the gas and residues in detail.The experimental results indicate that the colorant agent Fe2O3 inside the housing material is beneficial for the generation of mullite by decreasing the temperature of mullitization.Besides,since the transitional alumina generated by the dehydration of aluminum hydroxide(ATH)has a smaller diameter and can better dissolute into the silica phases,ATH is a better choice as the additional aluminum resource.By comparing the components,structure,and particle size of grains formed at different calcination temperatures,the proposed pyrolysis tem-peratures of the two stages are 1400℃ and 1600℃,respectively.
查看更多>>摘要：Compared to Si devices,the junction temperature of SiC devices is more critical due to the reliability concern introduced by immature packaging technology applied to new material.This paper proposes a practical SiC MOSFET junction temperature monitoring method based on the on-state voltage Vds(on)measurement.In Section Ⅱ of the paper,the temperature sensitivity of the on-state voltage Vds(on)is characterized.The hardware of the measurement system is set up in Section Ⅲ,which consists of an On-state Voltage Measurement Circuit(OVMC),the sampling and isolation circuit.Next,a calibration method based on the self-heating of the SiC MOSFET chip is presented in Section IV.In the final Section,the junction tem-perature is monitored synchronously according to the calibration results.The proposed method is applied to a Buck converter and verified by both an Infrared Radiation(IR)camera and a Finite Element Analysis(FEA)tool.
查看更多>>摘要：Repetitve nanosecond impulses in gas-insulated metal-enclosed switchgear(GIS)are likely to trigger inside flashover.Interface charges on the spacer in GIS are consid-ered one of the main factors damaging insulation performance and may be induced by overvoltage.For good understanding of insulation failures,accumulation characteristics of charges between SF6 and epoxy spacers under repetitive nanosecond impulses are investigated.It can be found under nanosecond impulses,the charge source in gas volume contributes to interface charge accumulation predominantly.Interface charges will be promoted by impulse number and amplitude.Accumulation processes are analyzed based on runaway electrons mechanism.When impulse amplitude exceeds a threshold value,discharge in the gas volume turns to a runaway mode.A runaway electron leads to the interface charge accumulation.Affected by motion of the runaway electrons,the potential peak gradually moves close to the grounded electrode when impulse amplitude is raised.Meanwhile,increasing impulse number can enhance surface potential.Surface potential will reach saturation eventually.However,memory effect of the repetitive impulse discharge makes the half-peak width of the surface potential at the interface change little.Design of GIS gas-solid insulations can refer to this research.
查看更多>>摘要：With high-frequency,low power dissipation and high-efficiency characteristics,Gallium nitride(GaN)power de-vices are of significant benefit in designing high-speed motor drives,as they improve performance and reduce weight.However,due to the cascode structure,coupling with the parasitics in gate driver and power circuits,power converters based on cascode GaN are prone to overshoot and oscillate on switching waveforms,which may lead to serious EMC problems,or even device breakdown.The complicated structure of cascode GaN device makes the gate driver design comparatively complex.An analytical model of the switching process considering gate driver parameters is proposed in this article.The influence of gate driver parameters on switching behavior is investigated from the perspective of switching speed,waveform overshoot,and power loss.Trade-offs among overshoot,switching speed,and power loss are discussed;guidelines to design gate driver parameters are given.
查看更多>>摘要：Environmental issues associated with the aviation industry are getting more attention as air traffic increases.Strin-gent standards are imposed for fuel consumption and pollution emissions for next-generation aircraft.Superconducting electrical propulsion aircraft(SEPA)have been seen as an efficient way to achieve this goal.High-temperature superconducting(HTS)devices are extensively used in the power system to supply enormous energy.Power is distributed to the different loads via a DC distribution network.However,it will generate an inrush current over ten times higher than the rated current in short-circuit state,which is very harmful to the system.Therefore,it is essential to adopt an appropriate protection scheme.This paper discusses one protection scheme that combines DC vacuum circuit breakers(DC VCB)and resistive superconducting cur-rent limiters(RSFCL)for superconducting aircraft applications.Considering problems of cost and loss,the auxiliary capacitor is pre-charged by system voltage,and mechanical elements extinguish the arc.Furthermore,combined with RSFCL,the interrupting environment is fully improved.RSFCL limits fault current,and then the VCB breaks this limited current based on creating an artificial current zero(ACZ).The prospective rated power is 8MW,rated voltage and current are 4 kV and 1 kA,respectively.In this paper,we discuss and simulate switching devices that protect SEPA.The interrupting performance of the circuit breaker is analysed in the DC short-circuit fault that occurs on the transmission line.Finally,the residual energy consumption of different situations is calculated.A comparison is made between using RSFCL with metal oxide varistor(MOV)and just using MOV.The scheme with RSFCL shows a significant advantage in energy consumption.
查看更多>>摘要：A virtual battery(VB)provides a succinct interface for aggregating distributed storage-like resources(SLR)to in-teract with a utility-level system.To overcome the drawbacks of existing VB models,including conservatism and neglecting network constraints,this paper optimizes the power and energy parameters of VB to enlarge its flexibility region.An optimal VB is identified by a robust optimization problem with decision-dependent uncertainty.An algorithm based on the Benders decomposition is developed to solve this problem.The proposed method yields the largest VB satisfying constraints of both network and SLRs.Case studies verify the superiority of the optimal VB in terms of security guarantee and less conservatism.
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