The Correlation between the Power Quality Indicators and Entropy Production Characteristics of Wind Power+Energy Storage Systems

Power quality improvements help guide and solve the problems of inefficient energy production and unstable power output in wind power systems.The purpose of this paper is mainly to explore the influence of different energy storage batteries on various power quality indicators by adding different energy storage devices to the simulated wind power system,and to explore the correlation between systementropy generation and various indicators,so as to provide a theoretical basis for directly improving power quality by reducing loss.A steady-state experiment was performed by replacing the wind wheel with an electric motor,and the output power qualities of the wind power systemwith andwithout energy storagewere compared and analyzed.Moreover,the improvement effect of different energy storage devices on various indicatorswas obtained.Then,based on the entropy theory,the loss of the internal components of the wind power system generator is simulated and explored by Ansys software.Through the analysis of power quality evaluation indicators,such as current harmonic distortion rate,frequency deviation rate,and voltage fluctuation,the correlation between entropy production and each evaluation indicator was explored to investigate effective methods to improve power quality by reducing entropy production.The results showed that the current harmonic distortion rate,voltage fluctuation,voltage deviation,and system entropy production are positively correlated in the tests and that the power factor is negatively correlated with system entropy production.In the frequency range,the frequency deviationwas not significantly correlated with the systementropy production.

Virtual Synchronous Generator Adaptive Control of Energy Storage Power Station Based on Physical Constraints

The virtual synchronous generator(VSG)can simulate synchronous machine’s operation mechanism in the control link of an energy storage converter,so that an electrochemical energy storage power station has the ability to actively support the power grid,from passive regulation to active support.Since energy storage is an important physical basis for realizing the inertia and damping characteristics in VSG control,energy storage constraints of the physical characteristics on the system control parameters are analyzed to provide a basis for the system parameter tuning.In a classic VSG control,its virtual inertia and damping coefficient remain unchanged.When the grid load changes greatly,the constant control strategy most likely result in the grid frequency deviation beyond the stable operation standard limitations.To solve this problem,a comprehensive control strategy considering electrified wire netting demand and energy storage unit state of charge(SOC)is proposed,and an adaptive optimization method of VSG parameters under different SOC is given.The energy storage battery can maintain a safe working state at any time and be smoothly disconnected,which can effectively improve the output frequency performance of energy storage system.Simulation results further demonstrated the effectiveness of the VSG control theoretical analysis.

An Investigation of Battery Energy Storage Aided Wind-Coal Integrated Energy System

This paper studies the feasibility of a supply-side wind-coal integrated energy system.Based on grid-side data,the load regulation model of coal-fired power and the wind-coal integrated energy system model are established.According to the simulation results,the reasons why the wind-coal combined power supply is difficult to meet the grid-side demand are revealedthrough scenario analysis.Basedon thewind-coal combinedoperation,a wind-coalstorage integrated energy system was proposed by adding lithium-iron phosphate battery energy storage system(LIPBESS)to adjust the load of the system.According to the four load adjustment scenarios of grid-side instructions of the wind-coal system,the difficulty of load adjustment in each scenario is analyzed.Based on the priority degree of LIPBESS charge/discharge in four scenarios at different time periods,the operation mode of two charges and two discharges per day was developed.Based on the independent operation level of coal-fired power,after the addition of LIPBESS(5.5 MWh),the average qualified rate of multi-power operation in March and June reached the level of independent operation of coal-fired power,while the average qualified rate of the remaining months was only 5.4%different from that of independent operation of coal-fired power.Compared with the wind storage mode,the energy storage capacity and investment cost of wind-coal-storage integrated energy system are reduced by 54.2%and 53.7%,respectively.

Self-charging power textiles integrating energy harvesting triboelectric nanogenerators with energy storage batteries/supercapacitors

Lightweight and flexible self-charging power systems with synchronous energy harvesting and energy storage abilities are highly desired in the era of the internet of things and artificial intelligences,which can provide stable,sustainable,and autonomous power sources for ubiquitous,distributed,and low-power wearable electronics.However,there is a lack of comprehensive review and challenging discussion on the state-of-the-art of the triboelectric nanogenetor(TENG)-based self-charging power textiles,which have a great possibility to become the future energy autonomy power sources.Herein,the recent progress of the self-charging power textiles hybridizing fiber/fabric based TENGs and fiber/fabric shaped batteries/supercapacitors is comprehensively summarized from the aspect of textile structural designs.Based on the current research status,the key bottlenecks and brighter prospects of self-charging power textiles are also discussed in the end.It is hoped that the summary and prospect of the latest research of self-charging power textiles can help relevant researchers accurately grasp the research progress,focus on the key scientific and technological issues,and promote further research and practical application process.

A novel coordinated control strategy considering power smoothing for a hybrid photovoltaic/battery energy storage system

This work presents a novel coordinated control strategy of a hybrid photovoltaic/battery energy storage(PV/BES) system. Different controller operation modes are simulated considering normal, high fluctuation and emergency conditions. When the system is grid-connected, BES regulates the fluctuated power output which ensures smooth net injected power from the PV/BES system. In islanded operation, BES system is transferred to single master operation during which the frequency and voltage of the islanded microgrid are regulated at the desired level. PSCAD/EMTDC simulation validates the proposed method and obtained favorable results on power set-point tracking strategies with very small deviations of net output power compared to the power set-point. The state-of-charge regulation scheme also very effective with SOC has been regulated between 32% and 79% range.

Battery Energy Storage to Strengthen the Wind Generator in Integrated Power System

The wind energy generation,utilization and its grid penetration in electrical grid are increasing world-wide.The wind generated power is always fluctuating due to its time varying nature and causing stability problem.This weak interconnection of wind generating source in the electrical network affects the power quality and reliability.The localized energy storages shall compensate the fluctuating power and support to strengthen the wind generator in the power system.In this paper,it is proposed to control the voltage source inverter （VSI） in current control mode with energy storage,that is,batteries across the dc bus.The generated wind power can be extracted under varying wind speed and stored in the batteries.This energy storage maintains the stiff voltage across the dc bus of the voltage source inverter.The proposed scheme enhances the stability and reliability of the power system and maintains unity power factor.It can also be operated in stand-alone mode in the power system.The power exchange across the wind generation and the load under dynamic situation is feasible while maintaining the power quality norms at the common point of coupling.It strengthens the weak grid in the power system.This control strategy is evaluated on the test system under dynamic condition by using simulation.The results are verified by comparing the performance of controllers.

Battery Energy Storage System and Demand Response Based Optimal Virtual Power Plant Operation

With certain controllability of various distribution energy resources (DERs) such as battery energy storage system (BESS), demand response (DR) and distributed generations (DGs), virtual power plant (VPP) can suitably regulate the powers access to the distribution network. In this paper, an optimal VPP operating problem is used to optimize the charging/discharging schedule of each BESS and the DR scheme with the objective to maximize the benefit by regulating the supplied powers over daily 24 hours. The proposed solution method is composed of an iterative dynamic programming optimal BESS schedule approach and a particle swarm optimization based (PSO-based) DR scheme approach. The two approaches are executed alternatively until the minimum elec-tricity cost of the whole day is obtained. The validity of the proposed method was confirmed with the obviously decreased supplied powers in the peak-load hours and the largely reduced electricity cost.

Applications of Lithium-Ion Batteries in Grid-Scale Energy Storage Systems

In the electrical energy transformation process,the grid-level energy storage system plays an essential role in balancing power generation and utilization.Batteries have considerable potential for application to grid-level energy storage systems because of their rapid response,modularization,and flexible installation.Among several battery technologies,lithium-ion batteries(LIBs)exhibit high energy efficiency,long cycle life,and relatively high energy density.In this perspective,the properties of LIBs,including their operation mechanism,battery design and construction,and advantages and disadvantages,have been analyzed in detail.Moreover,the performance of LIBs applied to grid-level energy storage systems is analyzed in terms of the following grid services:(1)frequency regulation;(2)peak shifting;(3)integration with renewable energy sources;and(4)power management.In addition,the challenges encountered in the application of LIBs are discussed and possible research directions aimed at overcoming these challenges are proposed to provide insight into the development of grid-level energy storage systems.

Wind Power Flow Optimization and Control System Based on Rapid Energy Storage

风电功率的间歇与波动致使电场容量可信度低、可调度性差；同时易引起局部电网的电压不稳、频率波动，影响了系统的电能质量及稳定性。针对此现象，将超级电容器与蓄电池组成快速储能装置，用于风电的潮流优化控制。采用三重双向直流变换电路控制储能元件间的功率流动；采用四象限交直流变换电路控制储能与电网间的能量交换。提出基于超级电容器电压低频波动抑制的功率分配方法，可显著减少蓄电池的充放次数；提出基于储能元件荷电状态的储能能量调整规则，可避免储能元件的过充和频繁深度放电，以优化其功率调节能力。实验结果表明，系统可实现2种储能元件的优势互补，能有效平滑调节风电注入电网的有功功率，并实时补偿控制风电接入点的无功功率。

Prospect of new pumped-storage power station

In this paper, a new type of pumped-storage power station with faster response speed, wider regulation range, and better stability is proposed. The operational flexible of the traditional pumped-storage power station can be improved with variable-speed pumped-storage tech no logy. Combined with chemical en ergy storage, the failure to achieve sec on d-order response speed and the insufficient safety and reliability of pumped-storage power units could be solved. With the better solar en ergy and site resources, the in teg rated performance can be improved by an optical storage system in stalled in future pumped-storage stations. Through the characteristics analysis of the new type of pumped-storage power station, three types of optimal station locations are proposed, namely, the load concentration area, new energy concentration area, and ultrahigh- voltage direct current receiver area. Taking the new pumped-storage power station as an example, the advantages of multi-energy cooperation and joint operation are analyzed. It can be predicted that the frequency and load regulation of the power grid will be more flexible, and the service capacity to the main power grid will be much stronger in the future.

Time-domain Differential Protection Based on Operating and Restraining Trajectory Indices for Lines Connecting Battery Storage Energy Stations

Battery energy storage stations(BESSs)pose sever-al challenges for both phasor-based differential protection and the newly-proposed time-domain differential protection.These challenges include low sensitivity and even rejection.Besides,the negative impact of various nonideal conditions,including current transformer(CT)saturation,errors,and outliers,on the security of differential protection remains an important problem.Motivated by the aforementioned issues,this study accounts for the trajectory distribution discrepancy on Cartesian plane under various conditions and proposes a time-domain differential protection method.In this paper,the trajectory formed by operating and restraining current samples is devel-oped.Subsequently,after considering different operating states,the fault severity levels,and nonideal conditions,the variances in trajectory distribution between internal and external faults are extensively analyzed.On this basis,the Cartesian plane is divided into operating,uncertainty,and restraining zones.Further,the operating and restraining trajectory indices are meticu-lously designed and a protection criterion based on these indices is formed to accurately separate internal faults from other events,unaffected by CT saturation,errors,and outliers.The exceptional performance of the proposed protection method is extensively validated through PSCAD simulations and a hard-ware-in-the-loop testing platform.Regarding the dependability,sensitivity,and security,the proposed protection method outper-forms three state-of-the-art differential protection methods.

Towards Implementation of Smart Grid: An Updated Review on Electrical Energy Storage Systems

A smart grid will require, to greater or lesser degrees, advanced tools for planning and operation, broadly accepted communications platforms, smart sensors and controls, and real-time pricing. The smart grid has been described as something of an ecosystem with constantly communication, proactive, and virtually self-aware. The use of smart grid has a lot of economical and environmental advantages;however it has a downside of instability and unpredictability introduced by distributed generation (DG) from renewable energy into the public electric systems. Variable energies such as solar and wind power have a lack of stability and to avoid short-term fluctuations in power supplied to the grid, a local storage subsystem could be used to provide higher quality and stability in the fed energy. Energy storage systems (ESSs) would be a facilitator of smart grid deployment and a “small amount” of storage would have a “great impact” on the future power grid. The smart grid, with its various superior communications and control features, would make it possible to integrate the potential application of widely dispersed battery storage systems as well other ESSs. This work deals with a detailed updated review on available ESSs applications in future smart power grids. It also highlights latest projects carried out on different ESSs throughout all around the world.

Recent Progress on Thermal Energy Storage for Coal-Fired Power Plant

With countries proposing the goal of carbon neutrality,the clean transformation of energy structure has become a hot and trendy issue internationally.Renewable energy generation will account for the main proportion,but it also leads to the problem of unstable electricity supply.At present,large-scale energy storage technology is not yet mature.Improving the flexibility of coal-fired power plants to suppress the instability of renewable energy generation is a feasible path.Thermal energy storage is a feasible technology to improve the flexibility of coal-fired power plants.This article provides a review of the research on the flexibility transformation of coal-fired power plants based on heat storage technology,mainly including medium to low-temperature heat storage based on hot water tanks and high-temperature heat storage based on molten salt.The current technical difficulties are summarized,and future development prospects are presented.The combination of the thermal energy storage system and coal-fired power generation system is the foundation,and the control of the inclined temperature layer and the selection and development of molten salt are key issues.The authors hope that the research in this article can provide a reference for the flexibility transformation research of coal-fired power plants,and promote the application of heat storage foundation in specific coal-fired power plant transformation projects.

Analysis of Hybrid Rechargeable Energy Storage Systems in Series Plug-In Hybrid Electric Vehicles Based on Simulations

In this paper, an extended analysis of the performance of different hybrid Rechargeable Energy Storage Systems (RESS) for use in Plug-in Hybrid Electric Vehicle (PHEV) with a series drivetrain topology is analyzed, based on simulations with three different driving cycles. The investigated hybrid energy storage topologies are an energy optimized lithium-ion battery (HE) in combination with an Electrical Double-Layer Capacitor (EDLC) system, in combination with a power optimized lithium-ion battery (HP) system or in combination with a Lithium-ion Capacitor (LiCap) system, that act as a Peak Power System. From the simulation results it was observed that hybridization of the HE lithium-ion based energy storage system resulted from the three topologies in an increased overall energy efficiency of the RESS, in an extended all electric range of the PHEV and in a reduced average current through the HE battery. The lowest consumption during the three driving cycles was obtained for the HE-LiCap topology, where fuel savings of respectively 6.0%, 10.3% and 6.8% compared with the battery stand-alone system were achieved. The largest extension of the range was achieved for the HE-HP configuration (17% based on FTP-75 driving cycle). HP batteries however have a large internal resistance in comparison to EDLC and LiCap systems, which resulted in a reduced overall energy efficiency of the hybrid RESS. Additionally, it was observed that the HP and LiCap systems both offer significant benefits for the integration of a peak power system in the drivetrain of a Plug-in Hybrid Electric Vehicle due to their low volume and weight in comparison to that of the EDLC system.

Method of Electric Powertrain Matching for Battery-powered Electric Cars

The current match method of electric powertrain still makes use of longitudinal dynamics, which can’t realize maximum capacity for on-board energy storage unit and can’t reach lowest equivalent fuel consumption as well. Another match method focuses on improving available space considering reasonable layout of vehicle to enlarge rated energy capacity for on-board energy storage unit, which can keep the longitudinal dynamics performance almost unchanged but can’t reach lowest fuel consumption. Considering the characteristics of driving motor, method of electric powertrain matching utilizing conventional longitudinal dynamics for driving system and cut-and-try method for energy storage system is proposed for passenger cars converted from traditional ones. Through combining the utilization of vehicle space which contributes to the on-board energy amount, vehicle longitudinal performance requirements, vehicle equivalent fuel consumption level, passive safety requirements and maximum driving range requirement together, a comprehensive optimal match method of electric powertrain for battery-powered electric vehicle is raised. In simulation, the vehicle model and match method is built in Matlab/simulink, and the Environmental Protection Agency (EPA) Urban Dynamometer Driving Schedule (UDDS) is chosen as a test condition. The simulation results show that 2.62% of regenerative energy and 2% of energy storage efficiency are increased relative to the traditional method. The research conclusions provide theoretical and practical solutions for electric powertrain matching for modern battery-powered electric vehicles especially for those converted from traditional ones, and further enhance dynamics of electric vehicles.

锂离子电池储能电站的热失控状态检测与安全防控技术研究进展

锂离子电池具有能量密度大、使用寿命长、工作温度范围宽、自放电小等优点,是中国电化学储能电站的主流电池技术。然而,在加热、过充等恶劣工况下,锂离子电池易发生热失控引发火灾甚至爆炸,因此其安全问题已逐渐成为锂离子电池储能电站建设及大规模应用的首要问题。该文系统分析了锂离子储能电池热失控的诱因、电池内部反应过程及外部特征参量的变化规律,重点总结了当前主要的电池热失控状态检测技术、智能诊断算法及储能电站安全防控技术,最后对储能电站热失控状态检测及安全防控技术进行了总结和展望。

计及深度调峰的风-光-水-火-抽蓄多能源联网系统优化调度研究

多种能源联网运行逐步成为未来电力系统发展的方向,多能源联网系统的优化调度是应对规模化新能源并网消纳的重要手段。文中建立了计及火电机组深度调峰成本的风-光-水-火-抽蓄联网系统成本模型和考虑调峰主动性的风-光-水-火-抽蓄联网系统日前优化调度模型。针对多能源耦合系统结构复杂的情况,提出了分层优化调度的模型求解策略。上层模型以净负荷波动最小为优化目标,得到等效负荷曲线;下层模型根据上层模型的调度结果,以调峰运行的经济性最优和新能源弃电率最低为目标函数,计及调峰主动性,求解考虑火电机组深度调峰煤耗特性的含新能源系统的经济调度问题。仿真算例表明所建模型实现了多能源联网系统的互补运行,提升了火电机组的深度调峰能力,降低新能源弃电率和系统运行成本。

光伏波动平抑下改进K-means的电池储能动态分组控制策略

针对电池储能系统(battery energy storage system,BESS)进行光伏波动平抑时寿命损耗高及荷电状态(state of charge,SOC)一致性差的问题,提出了光伏波动平抑下改进K-means的BESS动态分组控制策略。首先,采用最小最大调度方法获取光伏并网指令。其次,设计了改进侏儒猫鼬优化算法(improved dwarf mongoose optimizer,IDMO),并利用它对传统K-means聚类算法进行改进,加快了聚类速度。接着,制定了电池单元动态分组原则,并根据电池单元SOC利用改进K-means将其分为3个电池组。然后,设计了基于充放电函数的电池单元SOC一致性功率分配方法,并据此提出BESS双层功率分配策略,上层确定电池组充放电顺序及指令,下层计算电池单元充放电指令。对所提策略进行仿真验证,结果表明,所设计的IDMO具有更高的寻优精度及更快的寻优速度。所提BESS平抑光伏波动策略在有效平抑波动的同时,降低了BESS运行寿命损耗并提高了电池单元SOC的均衡性。

面向风电平抑的双电池单元储能系统功率分层优化控制策略

为减少风-储联合系统中,双电池单元储能系统的充放电循环次数,降低高充放电功率指令下电池单元充放电电流倍率,提出一种储能系统充放电功率分层优化控制策略。根据充放电功率指令高低,为两电池单元匹配同充同放和一充一放两种运行模式,同时优化设置两运行模式下电池荷电状态循环区间,平衡充放电电量。仿真验证表明,在风电平抑效果相同的情况下,所提策略可降低高充放电功率指令下电池单元充放电电流倍率,减少电池充放电循环次数,延长电池寿命,降低储能电池功率和容量的配置需求。

主动配电网-充换电站群-智慧社区群分层优化调度策略

为解决配电网、社区、充换电站3个利益主体之间难以保障能量最优交换和信息安全问题,提出一种主动配电网充换电站群智慧社区群的分层优化调度策略。首先,结合用户侧的储能需求和电动汽车充换电站的运行优化需求,在满足配电网经济运行的前提下建立电动汽车充换电站、配电网和社区共同参与的共享储能模式,上层为主动配电网运行模型,下层为社区和充换电站运行模型;其次,考虑各储能充换电站之间的交通流、能量流的时空特性,利用卡车对各电动汽车充换电站间的电池进行灵活调度,建立基于移动式储能车的电池时空共享模型;然后,为解决多主体(即充换电站、配电网、社区)参与的调度框架难以实现总体最优的问题,引入交替方向乘子法(alternating direction method of multipliers,ADMM)设计了社区充换电站配电网的3层能量共享模型;最后使用MATLAB对模型仿真编码求解。仿真结果表明:所提出的策略能够保障共享储能系统中各个主体隐私的安全性和用能的经济性,使能量共享形式更加多样化;可提高储能电池的使用效率和用能经济性,系统总成本降低了18%。