Centralized control of parallel connected power conditioning system in electric vehicle charge-discharge and storage integration station

This study presents a centralized control scheme that coordinates parallel operations of power conditioning system(PCS)for the grid interactions of electric vehicles(EVs)in EV charge-discharge and storage integration station.Key issues for the control and operation of PCS under various operation modes are discussed,including vehicle to grid(V2G)mode,stand-alone mode and seamless transfer mode.The intelligent multi-mode charge-discharge method is utilized for the V2G mode,and the parallel control method based on communication network is adopted for the standalone mode.In addition,a novel seamless transfer strategy is proposed,which is able to implement PCS transition between V2G mode and stand-alone mode.The detailed process of the seamless transfer between the two modes is illustrated.Experimental results are presented to show the performance and feasibility of this strategy.

Efficiency analysis of numerical integrations for finite element substructure in real-time hybrid simulation

Finite element（FE） is a powerful tool and has been applied by investigators to real-time hybrid simulations（RTHSs）. This study focuses on the computational efficiency, including the computational time and accuracy, of numerical integrations in solving FE numerical substructure in RTHSs. First, sparse matrix storage schemes are adopted to decrease the computational time of FE numerical substructure. In this way, the task execution time（TET） decreases such that the scale of the numerical substructure model increases. Subsequently, several commonly used explicit numerical integration algorithms, including the central difference method（CDM）, the Newmark explicit method, the Chang method and the Gui-λ method, are comprehensively compared to evaluate their computational time in solving FE numerical substructure. CDM is better than the other explicit integration algorithms when the damping matrix is diagonal, while the Gui-λ（λ = 4） method is advantageous when the damping matrix is non-diagonal. Finally, the effect of time delay on the computational accuracy of RTHSs is investigated by simulating structure-foundation systems. Simulation results show that the influences of time delay on the displacement response become obvious with the mass ratio increasing, and delay compensation methods may reduce the relative error of the displacement peak value to less than 5% even under the large time-step and large time delay.

Integrated construction technology for natural gas gravity drive and underground gas storage

Based on the mechanisms of gravity displacement,miscibility,viscosity reduction,and imbibition in natural gas flooding,an integrated reservoir construction technology of oil displacement and underground gas storage(UGS)is proposed.This paper systemically describes the technical connotation,site selection principle and optimization process of operation parameters of the gas storage,and advantages of this technology.By making full use of the gravity displacement,miscibility,viscosity reduction,and imbibition features of natural gas flooding,the natural gas can be injected into oil reservoir to enhance oil recovery and build strategic gas storage at the same time,realizing the win-win situation of oil production and natural gas peak shaving.Compared with the gas reservoir storage,the integrated construction technology of gas storage has two profit models:increasing crude oil production and gas storage transfer fee,so it has better economic benefit.At the same time,in this kind of gas storage,gas is injected at high pressure in the initial stage of its construction,gas is injected and produced in small volume in the initial operation stage,and then in large volume in the middle and late operation stage.In this way,the gas storage wouldn’t have drastic changes in stress periodically,overcoming the shortcomings of large stress variations of gas reservoir storage during injection-production cycle due to large gas injection and production volume.The keys of this technology are site selection and evaluation of oil reservoir,and optimization of gravity displacement,displacement pressure,and gas storage operation parameters,etc.The pilot test shows that the technology has achieved initial success,which is a new idea for the rapid development of UGS construction in China.

Integrated Techniques of Underground CO_2 Storage and Flooding Put into Commercial Application in the Jilin Oilfield, China

Global warming touches everybody＇s nerve, and direct reason for sharp increasing of CO2 in the atmosphere results mainly from the use of fossil fuel in power generation and other industries. How can humans return this ＂devil＂ to underground, and keep a peaceful environment for human？ Scientists from all over the world have been exploring them.

Public Auditing for Encrypted Data with Client-Side Deduplication in Cloud Storage

Storage auditing and client-side deduplication techniques have been proposed to assure data integrity and improve storage efficiency, respectively. Recently, a few schemes start to consider these two different aspects together. However, these schemes either only support plaintext data file or have been proved insecure. In this paper, we propose a public auditing scheme for cloud storage systems, in which deduplication of encrypted data and data integrity checking can be achieved within the same framework. The cloud server can correctly check the ownership for new owners and the auditor can correctly check the integrity of deduplicated data. Our scheme supports deduplication of encrypted data by using the method of proxy re-encryption and also achieves deduplication of data tags by aggregating the tags from different owners. The analysis and experiment results show that our scheme is provably secure and efficient.

Lowering the cost of large-scale energy storage:High temperature adiabatic compressed air energy storage

Compressed air energy storage is an energy storage technology with strong potential to play a significant role in balancing energy on transmission networks,owing to its use of mature technologies and low cost per unit of storage capacity.Adiabatic compressed air energy storage(A-CAES)systems typically compress air from ambient temperature in the charge phase and expand the air back to ambient temperature in the discharge phase.This papers explores the use of an innovative operating scheme for an A-CAES system aimed at lowering the total cost of the system for a given exergy storage capacity.The configuration proposed considers preheating of the air before compression which increases the fraction of the total exergy that is stored in the fom of high-grade heat in comparison to existing designs in which the main exergy storage medium is the compressed air itself.Storing a high fraction of the total exergy as heat allows reducing the capacity of costly pressure stores in the system and replacing it with cheaper thermal energy stores.Additionally,a configuration that integrates a system based on the aforementioned concept with solar thermal power or low-medium grade waste heat is introduced and thoroughly discussed.

Comparative Study on Methods for Computing Soil Heat Storage and Energy Balance in Arid and Semi-Arid Areas

Observations collected in the Badan Jaran desert hinterland and edge during 19-23 August 2009 and in the Jinta Oasis during 12-16 June 2005 are used to assess three methods for calculating the heat storage of the5-20-cm soil layer.The methods evaluated include the harmonic method,the conduction-convection method,and the temperature integral method.Soil heat storage calculated using the harmonic method provides the closest match with measured values.The conduction-convection method underestimates nighttime soil heat storage.The temperature integral method best captures fluctuations in soil heat storage on sub-diurnal timescales,but overestimates the amplitude and peak values of the diurnal cycle.The relative performance of each method varies with the underlying land surface.The land surface energy balance is evaluated using observations of soil heat flux at 5-cm depth and estimates of ground heat flux adjusted to account for soil heat storage.The energy balance closure rate increases and energy balance is improved when the ground heat flux is adjusted to account for soil heat storage.The results achieved using the harmonic and temperature integral methods are superior to those achieved using the conduction-convection method.

Multi-stage expansion planning of energy storage integrated soft open points considering tie-line reconstruction

With the rapid development of flexible interconnection technology in active distribution networks(ADNs),many power electronic devices have been employed to improve system operational performance.As a novel fully-con-trolled power electronic device,energy storage integrated soft open point(ESOP)is gradually replacing traditional switches.This can significantly enhance the controllability of ADNs.To facilitate the utilization of ESOP,device loca-tions and capacities should be configured optimally.Thus,this paper proposes a multi-stage expansion planning method of ESOP with the consideration of tie-line reconstruction.First,based on multi-terminal modular design characteristics,the ESOP planning model is established.A multi-stage planning framework of ESOP is then presented,in which the evolutionary relationship among different planning schemes is analyzed.Based on this framework,a multi-stage planning method of ESOP with consideration of tie-line reconstruction is subsequently proposed.Finally,case studies are conducted on a modified practical distribution network,and the cost-benefit analysis of device and multiple impact factors are given to prove the effectiveness of the proposed method.