Dynamic grouping control of electric vehicles based on improved k-means algorithm for wind power fluctuations suppression

To address the significant lifecycle degradation and inadequate state of charge(SOC)balance of electric vehicles(EVs)when mitigating wind power fluctuations,a dynamic grouping control strategy is proposed for EVs based on an improved k-means algorithm.First,a swing door trending(SDT)algorithm based on compression result feedback was designed to extract the feature data points of wind power.The gating coefficient of the SDT was adjusted based on the compression ratio and deviation,enabling the acquisition of grid-connected wind power signals through linear interpolation.Second,a novel algorithm called IDOA-KM is proposed,which utilizes the Improved Dingo Optimization Algorithm(IDOA)to optimize the clustering centers of the k-means algorithm,aiming to address its dependence and sensitivity on the initial centers.The EVs were categorized into priority charging,standby,and priority discharging groups using the IDOA-KM.Finally,an two-layer power distribution scheme for EVs was devised.The upper layer determines the charging/discharging sequences of the three EV groups and their corresponding power signals.The lower layer allocates power signals to each EV based on the maximum charging/discharging power or SOC equalization principles.The simulation results demonstrate the effectiveness of the proposed control strategy in accurately tracking grid power signals,smoothing wind power fluctuations,mitigating EV degradation,and enhancing the SOC balance.

Minimization of Reactive Power Fluctuation in JT-60SA Magnet Power Supply

This paper describes an asymmetric control method for the firing angle and a start/stop timing shift control of four thyristor converters called ＂Booster PS＂ to minimize the reactive power fluctuation during plasma initiation in JT-60SA. From the simulation using the ＂PSCAD/EMTDC＂ code, it is found that these control methods can drastically reduce the reac- tive power induced by the four units of the ＂Booster PS＂. In addition, the voltage fluctuation of the motor-generator connected to the ＂Booster PS＂ is expected to be suppressed. This can also contribute to achieve stable control of the JT-60SA magnet power supplies.

Influencing Factors of the Power Fluctuation on the Ultra High Voltage Transmission Line Caused by Faults at the Remote Ends of the Interconnected Grid

After the North China grid and the Central China grid get into connection with the UHVAC demonstration, a new phenomenon is discovered according to some simulations. That is, the faults at the remote end of the UHV interconnected grid will result in significant power fluctuation and voltage drop on the UHV transmission line and even system splitting. But the faults near the UHV line only have marginal effects. Further, the simulation results also indicate that the short-circuit current of the buses near the UHV line is larger than that of the buses far away from the UHV line. This phenomenon is divergent from the traditional view. In this paper, the detail will be introduced, and the factors influencing the system stability after faults are presented and analyzed. The results indicate that transmission power of the UHV line and of the lines between the remote end and the major grid influence the fluctuation on UHV line. The load model and the grid structure of the remote end also have effect on it. Finally, corresponding control scheme is presented to improve the operation conditions of the UHV interconnected grid and ensure its security and stability.

Research and Application of Probability Distribution of Wind Power Fluctuation Characteristics

The fluctuation characteristics is the inherent property of wind power.Through analysis of a large number of wind t＇anns based on measured data,we find it describes the best probability distribution of wind power fluctuation for the mixed Gauss distribution of two components,and try to carry out the physical interpretation of two components.Further discussion is between the probability distribution of fluctuating wind power time difference and whole relationship.It is found that the two have basic similarity.Through comparing the different time level data quantified losses the information of wind power fluctuation,quantitative determination of the degree of impact prediction.We can summarize and understand of wind power fluctuation,constructing instance from the wind farm construction and monitoring prediction two aspect recommendations to overcome the adverse effects of wind power fluctuations on the power grid operation.

Digitally Controlled Boost PFC Converters Operating with Large Scale Load Fluctuations

When boost power factor correction(PFC) circuit works with large scale load fluctuations, it is easy to cause a higher total harmonic distortion and a lower power factor because of traditional controllers and inductor current mode. To solve this problem, this paper proposes a PFC control system, which can operate with load fluctuations up to 1 000 W by using duty cycle feed-forward control theory to achieve smooth switching mode. The duty cycles in the next period of the control system are pre-estimated in the current cycle, which enhances the speeds of AD samplers and switching frequency, and reduces the cost and volume of the equipment to some extent. Introductions of system decoupling and feed-forward of input-voltage greatly improve the system performance. Both theoretical simulation and experimental results prove the advantage of the proposed scheme.

Measurement of Particle Velocity, Particle Size Distribution and Concentration in Particulate Suspension by Transmission Fluctuation Correlation Spectrometry

In coal-fired power generation industry, parameters such as particle size affect combustion efficiency. Especially in the application of two-phase flow clean energy, the parameters such as particle velocity, particle size distribution and concentration are very important, because the coal particle velocity, concentration or size range have an impact on the whole combustion process. This paper introduces an optical measurement setup based on the transmission fluctuation correlation spectrum measurement technique, which realizes the simultaneous measurement of particle velocity, particle size distribution and concentration. Compared with image method, ultrasonic spectrum method and other methods, the experimental device is simple and low-cost.

Research on typical operating conditions of hydrogen production system with off-grid wind power considering the characteristics of proton exchange membrane electrolysis cell

Hydrogen energy,with its abundant reserves,green and low-carbon characteristic,high energy density,diverse sources,and wide applications,is gradually becoming an important carrier in the global energy transformation and development.In this paper,the off-grid wind power hydrogen production system is considered as the research object,and the operating characteristics of a proton exchange membrane(PEM)electrolysis cell,including underload,overload,variable load,and start-stop are analyzed.On this basis,the characteristic extraction of wind power output data after noise reduction is carried out,and then the self-organizing mapping neural network algorithm is used for clustering to extract typical wind power output scenarios and perform weight distribution based on the statistical probability.The trend and fluctuation components are superimposed to generate the typical operating conditions of an off-grid PEM electrolytic hydrogen production system.The historical output data of an actual wind farm are used for the case study,and the results confirm the feasibility of the method proposed in this study for obtaining the typical conditions of off-grid wind power hydrogen production.The results provide a basis for studying the dynamic operation characteristics of PEM electrolytic hydrogen production systems,and the performance degradation mechanism of PEM electrolysis cells under fluctuating inputs.

基于单风电场功率波形幅-时特性的风电场群功率波动幅度演化建模与机理分析

大规模风电场群的功率波形是由场群内所有风电场功率波形累加而成。风电场群区域内风速时空分布的差异和风电场空间位置的分散导致各单风电场功率波形时序上的差异性,从而使场群功率的最大相对波动幅度低于单场功率的最大相对波动幅度,称为风电场群功率的汇聚效应。为了揭示汇聚效应的机理及其时空影响因素,该文根据各风电场功率波形具有相关性的特点,建立描述风电场群区域主要风速时空变化特征的一维风速行波函数,构建反映单风电场到风电场群功率波形演化关系的风电场群功率汇聚模型;基于离散小波变换构建反映风电功率波形多尺度变化特征的风电功率波形幅-时关联特性;深入分析风电场功率波形幅-时关联特性与风电场空间尺度的关联关系,建立基于单风电场功率波形幅-时关联特性的风电场群功率波动幅度评价方法,揭示单风电场功率波形特质及风电场空间间距影响风电场群功率波动幅度的机理。通过两个风电场群的实例验证所提模型和分析方法的有效性。

考虑波动功率耦合的电力电子变压器电容电压纹波抑制方法研究

级联型电力电子变压器通常采用大电容来抑制子模块的电容电压波动,这严重限制了电力电子变压器功率密度的提高。针对这一问题,文中首先推导了二倍频波动电压的产生机理和波动功率的耦合原理,然后从输入阻抗的角度对波动功率不能自然流入后级的原因进行了分析,进而提出了一种实时调整隔离级输入电流的电容电压纹波抑制策略,有效地降低了电容电压波动幅值,最后在PSCAD/EMTDC中搭建仿真模型,并与传统控制策略进行对比,验证了所提策略的有效性。

考虑海上风能波动的水下压缩空气储能系统能量转化特性

为准确揭示海上风能波动性对水下压缩空气储能系统性能的影响规律,以先进绝热水下压缩空气储能系统为研究对象,首先,建立考虑风能波动性的海上风电-储能系统热力学模型;接着,提出关键设计参数的设计流程;最后,分析了额定工况与变工况条件下储能系统的能量转化特性。研究结果表明:随着导热油与空气质量流量之比κ_(o,a)的增加,水下输气管道散热损失与冷油罐散热损失的变化趋势相反,同时存在κ_(o,a)最优值为1.41,使得系统热损失最小,对应的最大系统能量往返效率η_(rt)为60.3%;设计工况下,储热与换热单元的(火用)损失最大,约占总损失的36.6%;稳定风速下,当风速偏离设计基础风速时,压缩机与膨胀机的效率降低,导致η_(rt)降低;扰动风速下,随着扰动风分量最大值v_(d,max)增加,受风机额定风速与切出风速的限制,v_(d,max)对储能系统平均发电功率的影响区域可分为快速增长区、增长减缓区以及降低区,3个区域内的η_(rt)均低于额定稳定工况下的设计值。研究可为水下压缩空气储能与海上风电的集成应用提供理论指导。

海上风电发电量指数保险设计

中国发展海上风电面临风速偏小导致发电量减少的风险,给运营及投资方带来损失。本研究基于ERA5风场数据,评估中国近海风资源波动风险,设计海上风电发电量指数保险,并检验其效果。结果表明:(1)中国近海风资源以台湾海峡最高,东海及南海开阔海域优于渤海湾及北部湾区,且秋、冬季较春、夏季更为丰富。(2)近海风资源偏小事件的发生率随时间呈上升趋势。东海南部和台湾海峡发生频率最高,并由开阔海域向陆地逐渐减小,南海北部由西向东逐渐增大。波动强度在近海各岛屿的西侧较大。(3)发电量下行波动风险以台湾海峡最高,南海东北部和北部湾次之,黄海及东海北部、东海南部和南海西北部最小。(4)海上风电发电量指数保险以月实际发电量为指数,可有效反映风资源的月尺度差异,根据超越概率设置不同的月赔付触发阈值,提供不同风险保障程度的保险方案。费率厘定中考虑了管理低频高损事件风险所增加的保险成本及不同地域间的风险差异。月赔付触发电量取95、93和90超越概率水平时,其保障程度自低到高,对应的保险费率分别为7.045%、7.384%及8.685%。该保险产品可通过损失补偿及提高收入下限,稳定风电场收益,有效管理风资源波动风险。

陕西镇安抽水蓄能电站地下厂房动力响应分析

抽水蓄能电站水头高,地下厂房结构振动问题突出,启停频繁,地下厂房动力响应分析作为厂房设计研究中的重点问题受到更多关注。以陕西镇安抽水蓄能电站为例,利用ANSYS有限元软件建立地下厂房实体模型,通过进行厂房自振特性及共振分析和对机组荷载及压力脉动作用下地下厂房动力响应进行研究,分析了不同工况下厂房整体、局部结构自振特性和动力响应。结果表明:镇安抽水蓄能电站厂房抗振设计基本合理,楼梯和立柱作为厂房薄弱环节需重点关注;电站在低水头运行时,厂房结构动力响应明显增大,在实际运行中应合理调度,尽量减少低水头运行时长。研究结果可为类似工程设计提供参考。

Probability distribution of wind power volatility based on the moving average method and improved nonparametric kernel density estimation

In the process of large-scale,grid-connected wind power operations,it is important to establish an accurate probability distribution model for wind farm fluctuations.In this study,a wind power fluctuation modeling method is proposed based on the method of moving average and adaptive nonparametric kernel density estimation(NPKDE)method.Firstly,the method of moving average is used to reduce the fluctuation of the sampling wind power component,and the probability characteristics of the modeling are then determined based on the NPKDE.Secondly,the model is improved adaptively,and is then solved by using constraint-order optimization.The simulation results show that this method has a better accuracy and applicability compared with the modeling method based on traditional parameter estimation,and solves the local adaptation problem of traditional NPKDE.

Groundwater Waves in a Coastal Fractured Aquifer of the Third Phase Qinshan Nuclear Power Engineering Field

Tidal fluctuations of Hangzhou Bay produce progressive pressure waves in adjacent field fractured aquifers, as the pressure waves propagate, groundwater levels and hydraulic gradients continuously fluctuate. The effect of tidal fluctuations on groundwater flow can be determined using the mean hydraulic gradient that can be calculated by comparing mean ground and surface water elevations.Tidal fluctuation is shown to affect the piezometer readings taken in a nearshore fractured aquifer around the nuclear power engineering field. Continuous monitoring of a network of seven piezometers provided relations between the tidal cycle and the piezometer readings. The relations can be expressed in times of a time and amplitude scaling factor. The time lag and the tidal efficiency factor and wavelength are calculated using these parameters. It provides significant scientific basis to prevent tide and groundwater for the nuclear power engineering construction and safety run of nuclear power station in the future.

Analysis on the Characteristics of Wind Power Output in Hainan Power Grid

It is of great importance to study the characteristics of wind power output for the healthy and secure & stable of power grid. Based on the actual operating data, the probability distribution of the power fluctuations of the wind farm in Hainanand the variation of wind power annual, seasonal, daily active output is analyzed. The study showed thatHainanProvincehas obvious seasonal variation of wind power output characteristics, higher levels of output of the year generally in winter or summer, spring and autumn to contribute small. The average wind power output will contribute to “low day and high night”, with certain peaking capacity. Shorter time scales, changes in the wind power to smaller amount, not to bring too much impact on system operation, while a long time fluctuations affect the scheduling and running on the grid.

Impact of the Intermittency of Photovoltaic Power Plants on the Frequency Management: Case of the Senegalese Electricity Grid

This paper investigates the impact of the intermittency of the photovoltaic (PV) power plants on the electric grid frequency management and the consequences that can occur. To meet these purposes, three years data of the Senegalese grid frequency are used, combined with three PV power plants data since their starting-up. Using these data, we analyzed two days of heavily disturbed operation of the Senegalese grid in order to emphasize the real impact of the presence of PV power plants on the electrical grid. Our study has highlighted that how the intermittency of photovoltaic power plants affects frequency management. It obviously appears that the PV production curves follow the irradiation variations. Instantaneous variations of PV production make it difficult to manage the grid frequency leading to more frequent load shedding as we have shown with the data after the commissioning of the PV power plants. We also estimate the power then energy losses during the load shedding induced by the PV integration on the power grid by comparing a period corresponding to one month before (February 2017) and one month after (February 2018) the integration of variable PV production.

Coordinated control strategy for wind power accommodation based on electric heat storage and pumped storage

To solve the severe problem of wind power curtailment in the winter heating period caused by ＂power determined by heat＂ operation constraint of cogeneration units, this paper analyzes thermoelectric load, wind power output distribution and fluctuation characteristics at different time scales, and finally proposes a two level coordinated control strategy based on electric heat storage and pumped storage. The optimization target of the first level coordinated control is the lowest operation cost and the largest wind power utilization rate. Based on prediction of thermoelectric load and wind power, the operation economy of the system and wind power accommodation level are improved with the cooperation of electric heat storage and pumped storage in regulation capacity. The second level coordinated control stabilizes wind power real time fluctuations by cooperating electric heat storage and pumped storage in control speed. The example results of actual wind farms in Jiuquan, Gansu verifies the feasibility and effectiveness of the proposed coordinated control strategy.

Analysis of Cooperation between Wind Power and Load Side Resources

Development of the intermittent energy is greatly promoted by change in energy, while consumption of large-scale intermittent energy is becoming a problem. With the development of smart grid technology, controllability of load side resources is becoming more and more important. Based on the wave characteristics of wind power, this paper indicates that wind energy has continuous output characteristics on the hour-time scale. Through analysis on loads characteristic of industry, public facility and resident, this paper gets comprehensive response of load side resources. Considering characteristics of wind power output, combined with different load side resources and DR program, this paper suggests cooperation between wind power and load side resources on different time scales.

平抑风电波动的电-氢混合储能容量优化配置

针对电-氢混合系统协同平抑接入新型电力系统的新能源波动问题,提出考虑碱性电解槽运行特性的电-氢混合储能容量优化配置方案。首先,基于经验模态分解,将原始风电功率信号分解为符合波动量限值的直接并网分量和混合储能功率任务;在综合考虑电化学储能和氢储能介质充放电功率约束和存储状态约束的基础上,制定计及碱性电解槽运行特性的混合储能能量管理策略。基于此策略,以综合成本最小为目标,建立用于平抑风电波动的电-氢混合储能容量配置模型,并通过实际数据进行计算分析。算例结果表明,所提策略下的容量配置方案,在满足平抑需求的前提下,可以有效提高系统经济性。

计及SOC自恢复的混合储能平抑风电功率波动控制

混合储能系统能够较好地应对复杂的风电波动,有效地提高电网的稳定性和安全性。在混合储能平抑风电功率波动的典型应用场景下,该文首先提出一种计及荷电状态(SOC)自恢复的混合储能平抑风电功率波动控制方法,在满足风电平抑需求的情况下,通过模型预测控制快速调节储能在平抑功率过程中的荷电状态,提高储能持续稳定运行能力;然后,为提高混合储能系统协调运行能力,设计了加权滑动平均(WMA)-模糊控制策略对超级电容和蓄电池功率进行动态分配;最后,结合实际风电功率数据,通过仿真验证了所提策略能有效平衡储能寿命和平抑风电波动的矛盾,能充分考虑两种储能设备的特性差异并提高功率分配的合理性。