Minimization and control of battery energy storage for wind power smoothing: Aggregated,distributed and semi-distributed storage

A battery energy storage system (BESS) is usually integrated with a wind farm to smooth out its intermittent power in order to make it more dispatchable. This paper focuses on the development of a scheme to minimize the capacity of BESS in a distributed configuration using model predictive control theory and wind power prediction. The purpose to minimize the BESS capacity is to reduce the overall cost of the system as the capacity of BESS is the main cost driver. A new semi-distributed BESS scheme is proposed and the strategy is analyzed as a way of improving the suppression of the fluctuations in the wind farm power output. The scheme is tested for similar and dissimilar wind power profiles, where the turbines are geographically located closer and further from each other, respectively. These two power profiles are assessed under a variety of hard system constraints for both the proposed and conventional BESS configurations. Based on the simulation results validated with real-world wind farm data, it has been observed that the proposed semi-distributed BESS scheme results in the improved performance as compared with conventional configurations such as aggregated and distributed storage.     

电网不同故障下DFIG特性分析及保护措施建议

目前,国内外对DFIG的研究主要侧重于风力发电机组控制策略方面,而对于不同电网故障情况下DFIG的运行特性分析较少。鉴于此,在DIgSILENT／PowerFactory下建立TDFIG模型,利用含风电场的WSCC三机九节点仿真系统,进行了电网不同故障情况下的一系列仿真,重点分析了电网不同故障情况下DFIG的运行特性,研究了风电场与电网之间的交互影响及相应的保护措施,为大规模风电接入电网的运行控制提供依据。     

Techno‐economic optimization of hybrid power system using genetic algorithm

This paper presents an optimum sizing methodology to optimize the hybrid energy system (HES) configuration based on genetic algorithm. The proposed optimization model has been applied to evaluate the techno‐economic prospective of the HES to meet the load demand of a remote village in the northern part of Saudi Arabia. The optimum configuration is not achieved only by selecting the combination with the lowest cost but also by finding a suitable renewable energy fraction that satisfies load demand requirements with zero rejected loads. Moreover, the economic, technical and environmental characteristics of nine different HES configurations were investigated and weighed against their performance. The simulation results indicated that the optimum wind turbine (WT) selection is not affected only by the WT speed parameters or by the WT rated power but also by the desired renewable energy fraction. It was found that the rated speed of the WT has a significant effect on optimum WT selection, whereas the WT rated power has no consistent effect on optimal WT selection. Moreover, the results clearly indicated that the HES consisting of photovoltaics (PV), WT, battery bank (Batt) and diesel generator (DG) has superiority over all the nine systems studied here in terms of economical and environmental performance. The PV/Batt/DG hybrid system is only feasible when wind resource is very limited and solar energy density is high. On the other hand, the WT/Batt/DG hybrid system is only feasible at high wind speed and low solar energy density. It was also found that the inclusion of batteries reduced the required DG and hence reduced fuel consumption and operating and maintenance cost. Copyright © 2014 John Wiley & Sons, Ltd.     

Managing peak loads in energy grids: Comparative economic analysis

One of the key issues in modern energy technology is managing the imbalance between the generated power and the load, particularly during times of peak demand. The increasing use of renewable energy sources makes this problem even more acute. Various existing technologies, including stationary battery energy storage systems (BESS), can be employed to provide additional power during peak demand times. In the future, integration of on-board batteries of the growing fleet of electric vehicles (EV) and plug-in hybrid electric vehicles (PHEV) into the grid can provide power during peak demand hours (vehicle-to-grid, or V2G technology).This work provides cost estimates of managing peak energy demands using traditional technologies, such as maneuverable power plants, conventional hydroelectric, pumped storage plants and peaker generators, as well as BESS and V2G technologies. The derived estimates provide both per kWh and kW year of energy supplied to the grid. The analysis demonstrates that the use of battery storage is economically justified for short peak demand periods of <1 h. For longer durations, the most suitable technology remains the use of maneuverable steam gas power plants, gas turbine,reciprocating gas engine peaker generators, conventional hydroelectric, pumped storage plants.     

Lifetime and economic analyses of lithium‐ion batteries for balancing wind power forecast error

Wind power plant operators are often faced with extra charges when their power production does not match the forecasted power. Because the accuracy of wind power forecasts is limited, the use of energy storage systems is an attractive alternative even when large‐scale aggregation of wind power is considered. In this paper, the economic feasibility of lithium‐ion batteries for balancing the wind power forecast error is analysed. In order to perform a reliable assessment, an ageing model of lithium‐ion battery was developed considering both cycling and calendar life. The economic analysis considers two different energy management strategies for the storage systems and it is performed for the Danish market. Analyses have shown that the price of the Li‐ion BESS needs to decrease by 6.7 times in order to obtain a positive net present value considering the present prices on the Danish energy market. Moreover, it was found that for total elimination of the wind power forecast error, it is required to have a 25‐MWh Li‐ion battery energy storage system for the considered 2 MW WT. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling,design, and optimization of a cost‐effective and reliable hybrid renewable energy system integrated with desalination using the division algorithm

People in the Middle East are facing the problem of freshwater shortages. This problem is more intense for a remote region, which has no access to the power grid. The use of seawater desalination technology integrated with the generated energy unit by renewable energy sources could help overcome this problem. In this study, we refer a seawater reverse osmosis desalination (SWROD) plant with a capacity of 1.5 m³/h used on Larak Island, Iran. Moreover, for producing fresh water and meet the load demand of the SWROD plant, three different stand‐alone hybrid renewable energy systems (SAHRES), namely wind turbine (WT)/photovoltaic (PV)/battery bank storage (BBS), PV/BBS, and WT/BBS are modeled and investigated. The optimization problem was coded in MATLAB software. Furthermore, the optimized results were obtained by the division algorithm (DA). The DA has been developed to solve the sizing problem of three SAHRES configurations by considering the object function's constraints. These results show that this improved algorithm has been simpler, more precise, faster, and more flexible than a genetic algorithm (GA) in solving problems. Moreover, the minimum total life cycle cost (TLCC = 243 763$), with minimum loss of power supply probability (LPSP = 0%) and maximum reliability, was related to the WT/PV/BBS configuration. WT/PV/BBS is also the best configuration to use less battery as a backup unit (69 units). The batteries in this configuration have a longer life cycle (maximum average of annual battery charge level) than two other configurations (93.86%). Moreover, the optimized results have shown that utilizing the configuration of WT/PV/BBS could lead to attaining a cost‐effective and green (without environmental pollution) SAHRES, with high reliability for remote areas, with appropriate potential of wind and solar irradiance.     

风电接入对安庆地区电网的影响

为研究风电接入对安庆电网的影响,根据风功率的转换特性及双馈感应电机的运行特性,建立了风电场的风功率模型及双馈感应电机的动态模型,利用中国版BPA软件分析了风电接入系统后对电网静态电压稳定性、网损、短路电流及电网暂态稳定性的影响。结果表明,风电接入后电网电压满足正常运行要求,有利于网损的减小,但增大了短路点的短路电流;此外,由于风电容量较小,风电接入对电网暂态稳定性影响不大。可见,风电接入后安庆电网能安全经济运行。     

Dynamic contribution of variable-speed wind energy conversion system in system frequency regulation

Frequency regulation in a generation mix having large wind power penetration is a critical issue, as wind units isolate from the grid during disturbances with advanced power electronics controllers and reduce equivalent system inertia. Thus, it is important that wind turbines also contribute to system frequency control. This paper examines the dynamic contribution of doubly fed induction generator (DFIG)-based wind turbine in system frequency regulation. The modified inertial support scheme is proposed which helps the DFIG to provide the short term transient active power support to the grid during transients and arrests the fall in frequency. The frequency deviation is considered by the controller to provide the inertial control. An additional reference power output is used which helps the DFIG to release kinetic energy stored in rotating masses of the turbine. The optimal speed control parameters have been used for the DFIG to increases its participation in frequency control. The simulations carried out in a two-area interconnected power system demonstrate the contribution of the DFIG in load frequency control.     

Optimal reactive power allocation in an offshore wind farms with LCC-HVdc link connection

This paper addresses the optimal operation of an offshore wind farms (OWF), consisting of 120 wind turbines with doubly fed induction generators (DFIG) and a high voltage dc (HVdc) connection with the grid, using line commutated converters (LCC). For an optimal operation of the OWF, the distribution of the reactive power set points throughout the wind turbine generators must be optimal, in order to achieve minimum losses within the wind farm and the HVdc transmission system and therefore obtain the maximum production output. To accomplish this objective, an optimization formulation has been proposed which includes a complete model of the OWF and the LCC-HVdc, and the study of two different configurations. Simulation results show the advantages of using the reactive capability of the DFIG to achieve the optimal operation of the OWF.     

A Statistical Approach to the Design of a Dispatchable Wind Power-Battery Energy Storage System

A scheme that allows the dispatch of steady and controllable level of power from a wind power generating station is proposed in this paper. The scheme utilizes two battery energy storage systems (BESSs) in which the generated wind power is used to charge one BESS, while the second BESS is used to discharge constant power into grid. The role of the two BESS interchanges when the discharging BESS reaches specified operating limit. With this scheme in mind and based on given wind speed statistics, charging characteristics of the BESS are studied, and a method to determine the expected charging time of the BESS to reach stipulated battery state of charge is developed. The expected BESS charging time, in turn, dictates the constant power level that can be dispatched to the grid through the discharging BESS. The corresponding discharge time is also determined using the developed method, the accuracy of which is validated experimentally. The proposed design procedure is then used to determine the minimum BESS capacity based on the expected wind power. Statistical likelihood of dispatchable power delivery achievable from the scheme is also obtained.      

Predictive control and sizing of energy storage to mitigate wind power intermittency

This paper studies how the control algorithm impacts the required capacity of battery energy storage system (BESS) to mitigate wind intermittency. We study a futuristic scenario in which wind generation is traded in the energy market on an hourly basis, and the wind power producer has to procure reserves to handle wind fluctuations. The wind power producer can avoid paying for conventional reserves by charging/discharging BESS to compensate for wind surplus and deficit. We develop control algorithms using the model predictive control (MPC) methodology, which incorporates wind forecasts for the next few hours when determining wind scheduling. The MPC algorithm is developed by solving a non‐linear optimization problem to minimize operation costs to the wind power producer. In addition to operation costs, the MPC algorithm considers two practical aspects: the efficiency loss of BESS and the smoothness in wind power scheduling. BESS sizing is studied by parametric analyses. Simulations show that BESS is more effective in reducing operation costs and reducing wind curtailment than conventional reserves. In addition, MPC is a horizon‐based control algorithm and can preview future information in its control action. Simulations also show that MPC consistently outperforms an instantaneous heuristic algorithm that does not use future information. Therefore, we confirm that MPC can reduce the BESS capacity required to cover wind uncertainties. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantitative and qualitative behavior analysis of a DFIG wind energy conversion system by a wind gust and converter faults

A wind gust can cause severe dynamic conditions that affect the operational behavior of the whole doubly fed induction generator (DFIG) wind energy conversion system and, as a result, the quality of power exchanged with the grid. In addition, it can cause great disturbances to critical system's variables with possible damages to the system's construction—to mechanical or electrical part. The knowledge of DFIG reaction in such conditions is useful for both protection issues and the risk assessment concerning system's tolerance, maintenance costs and revenue losses, because of the disconnection from the grid. In this paper, a quantitative and qualitative behavior analysis of a 2 MW DFIG wind energy conversion system under a wind gust and converter faults, which has been carried out via simulation, is presented. The pitch controller parameters impact to its behavior, when a gust appears, has been investigated. Copyright © 2015 John Wiley & Sons, Ltd.     

An analysis for the need of a battery energy storage system in tracking wind power schedule output

电池储能系统(battery energy storage system,BESS)在风储联合应用中具有多种功能,利用电池储能系统提高风电并网调度运行能力是当前研究的热点之一.文章基于我国北方某风电场历史运行数据与预测数据,依据预测误差评价指标和风电场预报考核指标的综合评价方法对风电场预测数据进行分析研究,归纳了预测误差的概率分布特征;提出利用电池储能系统提高风电跟踪计划出力能力,统计并量化出电池储能系统用于跟踪计划出力场合的作用范围;通过仿真验证电池储能系统在风储联合系统中提高风电跟踪计划出力控制策略的有效性和可行性.     

Compensation of network voltage unbalance using doubly fed induction generator-based wind farms

A control strategy for compensating AC network voltage unbalance using doubly fed induction generator (DFIG)-based wind farms is presented. A complete DFIG dynamic model containing both the rotor and grid side converters is used to accurately describe the average and ripple components of active/reactive power, electromagnetic torque and DC bus voltage, under unbalanced conditions. The principle of using DFIG systems to compensate grid voltage unbalance by injecting negative sequence current into the AC system is described. The injected negative sequence current can be provided by either the grid side or the rotor side converters. Various methods for coordinating these two converters are discussed and their respective impacts on power and torque oscillations are described. The validity of the proposed control strategy is demonstrated by simulations on a 30 MW DFIG-based wind farm using Matlab/Simulink during 2 and 4% voltage unbalances. The proposed compensation strategy can not only ensure reliable operation of the wind generators by restricting torque, DC link voltage and power oscillations, but also enable DFIG-based wind farms to contribute to rebalancing the connected network.     

Design and set up of a hybrid power system (PV-WT-URFC) for a stand-alone application in Mexico

The Mexican territory has a large potential for renewable energy development, such as geothermal, hydro, biofuels, wind and solar. Thus, a 2.5 kW hybrid power system (solar, wind and hydrogen) was designed and installed to meet the power demand for a stand-alone application at the University of Zacatecas. The hybrid unit integrates three power energy sources –a photovoltaic system (PV), a micro-wind turbine (WT), a prototype of a unitized regenerative fuel cell (URFC) and energy storage devices (batteries)– in addition to their interaction methodology. The main contribution of this work is the URFC integration to a hybrid power system for the production of H₂ (water electrolyzer mode) and energy (fuel cell mode). These three energy technologies were connected in parallel, synchronized to the energy storage system and finally coupled to a power conversion module. To achieve the best performance and energy management, an energy management and control strategy was developed to the properly operation of the power plant. A meteorological station that has wireless sensors for the temperature, the humidity, the solar radiation and the wind speed provides the necessary information (in real time) to the monitor and control software, which computes and executes the short and mid–term decisions about the energy management and the data storage for future analysis.     

Dynamic performance of wind-diesel power system with capacitive energy storage

This paper presents an analysis of the dynamic performance of a wind-Diesel power system which operates in isolation from the grid. The simulation studies of the dynamic response are conducted in two different configurations of the power system, firstly, without storage and, secondly, with capacitive energy storage. The frequency and power deviations resulting from a step load disturbance of 1% are presented. It is shown that improvement in the transient responses of the stand alone wind and the hybrid wind-Diesel power system is achieved when capacitive energy storage is included in the systems.     

基于改进支持向量机的多能源电力系统中储能容量规划及运行模型

研究多能源电力系统中储能装置的定容及运行,有利于减小功率波动,降低对电网的冲击,提高电能质量。以青海省海西千万瓦级可再生能源基地为例,首先根据光伏电站和风电场的历史数据分析了两种新能源发电系统的出力特性,在此基础上建立了支持向量机模型,对新能源电站的输出功率进行了短期预测。根据光伏电站和风电场的出力预测误差,建立了ARMA误差预测模型,进一步修正了光伏电站和风电场的预测曲线,最后根据出力预测曲线的功率谱确定了储能系统的容量及出力曲线。研究成果可为新能源并网提供技术支持。     

Economic evaluation of fast charging electric vehicle station with second-use batteries energy storage system

由于电动汽车快速充电站大功率快速充电的特性会对电网的稳定造成冲击,因此考虑在电动车快速充电站中配置电池储能系统（BESS）,对充电站负荷进行削峰填谷,从而减少充电站变压器配置容量、缓解大功率快速充电对电网的不利影响。考虑到目前我国大量退役动力电池亟待回收利用的现状,结合梯次利用电池储能系统,建立了基于电动汽车快速充电站整体成本与收益的经济性评估模型,以快速充电站年净收益最大为目标函数,采用改进的遗传算法对模型优化求解。结合算例对快速充电站不配置储能、配置常规电池储能和配置梯次电池储能等不同情况进行了经济性评估,并综合考虑经济性与储能削减负荷的效果,确定了梯次电池储能系统最优容量配置方案。     

一种新型双电池风力发电储能系统及控制策略

提出一种新型双电池风电储能系统,它能以较低的运行成本将风电功率波动维持在规定的范围内;风电场可在每个调度时段内输出恒定功率,使风电稳定地并入电网。当调度功率低于实际风电功率时,起充电作用的电池处于工作状态,当调度功率高于实际风电功率时,起放电作用的电池处于工作状态;当其中一个电池充满电或深度放电时,2组电池的充、放电状态切换。为了延长电池使用寿命,对调度功率进行优化,以确保2组电池都在完整充、放电循环下运行,此双电池储能系统可显著降低系统运行成本。利用一台具有真实风电功率数据的3 MW风电机组进行仿真分析,验证了所提系统及控制策略的有效性。     

Comparative study on the performance of control systems for doubly fed induction generator (DFIG) wind turbines operating with power regulation

As a result of the increasing wind power penetration on power systems, the wind farms are today required to participate actively in grid operation by an appropriate generation control. This paper presents a comparative study on the performance of three control strategies for DFIG wind turbines. The study focuses on the regulation of the active and reactive power to a set point ordered by the wind farm control system. Two of them (control systems 1 and 2) are based on existing strategies, whereas the third control system (control system 3) presents a novel control strategy, which is actually a variation of the control system 2. The control strategies are evaluated through simulations of DFIG wind turbines, under normal operating conditions, integrated in a wind farm with centralized control system controlling the wind farm generation at the connection point and computing the power reference for each wind turbine according to a proportional distribution of the available power. The three control systems present similar performance when they operate with power optimization and power limitation strategies. However, the control system 3 with down power regulation presents a better response with respect to the reactive power production, achieving a higher available reactive power as compared with the other two. This is a very important aspect to maintain an appropriate voltage control at the wind farm bus.