With the development of renewable energy,the voltage support strength of multi-infeed systems with renewable energy is gradually decreasing,and there is an urgent need for strength evaluation methods.Considering that devices are all at the rated operation condition points,accurate quantification of strength can be achieved by utilizing existing power grid strength indices and threshold.However,the actual operation conditions of devices are diverse and complex,which disrupts the existing criteria for defining indices and causes existing methods to fail.Therefore,this paper focuses on the quantification problem of voltage support strength under actual operation conditions.Based on the perturbation theory of eigen-subspaces,an equivalent single-infeed system that can approximately characterize the stability of the actual system is solved.On this basis,the definition and physical significance of the generalized operational short-circuit ratio are provided,so as to rigorously quantify the strength under actual operation conditions using the generalized operational short-circuit ratio and the critical operational short-circuit ratio for devices.In addition,this paper reveals the specific mechanism of the actual operation conditions on strength with different stable forms.Finally,the effectiveness of the proposed method is verified through cases.
Accurate real-time topology identification of distribution networks is the basis for safe and stable operation of power systems,but with the access of renewable energy and the increasing scale of distribution network,the dynamic changes of the distribution network topology are more frequent and difficult to identify.However,the historical data used by the existing topology identification algorithms need to be labeled manually,and the topology identification time is long.So it is difficult to achieve real-time topology identification for distribution networks.Therefore,a real-time two-stage topology identification algorithm for distribution networks based on field programmable logic gate array(FPAG)is proposed.The proposed algorithm does not need to know the number of distribution network topology categories in advance,and can label and classify the existing historical data,and realize the real-time topology identification for distribution networks based on FPGA.The algorithm is divided into two stages.The first stage uses the variational Bayesian Gaussian mixture model to label and classify the existing historical data.In the second stage,the sparrow search algorithm is used to make the support vector machine converge quickly to get the optimal parameters,so as to realize the accurate topology identification for distribution networks.Based on this algorithm,a real-time topology identification platform is established by using FPGA parallel architecture and high speed and high density characteristics.Finally,the effectiveness and superiority of the proposed identification method are verified by case analysis.
Penetration of distributed renewable energy (DRE) is increasing in modern power systems. Integration of DREs have profound impact on transient voltage stability of bulk power systems, which has been observed in real-world power system event in USA and Australia. However, related studies are relatively rare in existing literatures. This paper utilizes a synthesis load model with renewables to study this issue. Two abnormal transient performances of DRE are revealed, which impact and interact with voltage of bulk power system. The performances are concluded as continuous low-voltage-ride-through (LVRT) of DRE and repeated LVRT of DRE, respectively. Sensitivities of the performances to DRE parameters are studied in weak power grid, with several novel and unexpected findings. Active power output of DRE significant influences the terminal voltage during LVRT, while impact of reactive output is not so prominent. Related results explain performance of several real power grids with high penetration of DREs.
As the proportion of wind power in new-type power systems increases year by year, its dynamic characteristics, especially fault ride-through characteristics, have a significant impact on power systems. To accurately analyze the impact of large-scale wind power on power systems, it is necessary to construct a white-box model that can characterize the actual dynamic characteristics of wind turbine. The white-box model has numerous parameters with interactive effects, and current parameter identification methods cannot achieve identification of the entire DFIG's fault ride-through, inner and outer controller parameters, limiting parameters, and electrical parameters, especially the accurate identification of parameters insensitive to external characteristics. To solve these problems, this paper constructs a frequency domain universal model for DFIG under fault ride-through conditions, which includes the DFIG itself and all controllers. The parameters are divided into four categories for step-by-step identification, proposing a categorized and integrated step-by-step identification method. The accuracy of the frequency domain universal model is verified through comparison with a simulation model, and the correctness of the proposed categorized and integrated step-by-step parameter identification method is validated by comparing the identified values with the real values.
The penetration of high-proportion renewable energy brings significant volatility and uncertainty to power grids.Thus the receiving end of the power system faces the problem of insufficient adjustable resource capacity.It requires the full utilization of a large number of flexible energy resources to participate in power system dispatch and provide auxiliary services.However,the vast number,wide distribution,and diverse characteristics of these flexible energy resources pose significant challenges to centralized dispatch and control.It is necessary to manage and dispatch these flexible energy resources in a clustered way.To accurately assess the role of clusters in the power system dispatch and control,it is essential to aggregate these flexible energy resources and evaluate their performance by using appropriate quantitative metrics based on application requirements.According to the application demands of flexible resource clusters in power system dispatch and electricity market,a quantitative metric system of flexibility for evaluating the adjustable capacity of flexible energy resource clusters is proposed.Based on their physical characteristics,these resources are categorized into three types:generator-like characteristics,storage-like characteristics,and common characteristics.For quantitative evaluation of the cluster flexibility metrics across various application scenarios,an aggregation reference model comprising an equivalent generator and an equivalent energy storage is proposed.This aggregation reference model has a clear physical interpretation,exhibits nested properties,and therefore is suitable for various time scales and energy forms.It can be used to calculate the quantitative metrics for specific application scenarios and widely applied in scenarios such as asynchronous dispatch of distributed energy resource clusters,joint optimization dispatch of integrated energy systems,and participation of virtual power plant in electricity market bidding.
When wind turbines participate in primary frequency regulation by releasing the kinetic energy of the rotor, the primary frequency response capacity (PFRC) varies with the fluctuation of operation conditions, especially the wind speed. Probabilistic Assessment of PFRC is required to provide basis for power system operation planning and control strategy formulation. A simplified analytical model of frequency response considering the dynamic variation of rotor speed was established. Based on the analytical solution of PFRC, the influence of wind speed on the PFRC was analyzed. Point estimation and Gram-Charlier series expansion were used to obtain the probabilistic distribution characteristics of PFRC with wind speed fluctuation. The accuracy of the model and the effectiveness of the proposed probabilistic evaluation method were verified by simulation.
Traditionally, virtual inertia is used as the control strategy for wind turbines when participating in frequency regulation. However, it has inherent defects in measurement error amplification due to the frequency differential. Also, when control delay of wind turbines is taken into consideration, virtual inertia is essentially a fast power response, just the same as droop control. Hence, considering the adaptability of droop control, it is valuable to explore a novel droop control method without virtual inertia, as the frequency response model of wind turbines. For this reason, a multi-segment droop control strategy is proposed to provide a reliable frequency regulation model for wind turbines that can be broadly applied to other inverter-based power sources. Firstly, based on the extended system frequency response model, a differential equation including piecewise time-varying coefficients is established, and the analytical expression of the frequency response is obtained using the impulse function balancing principle and the integration by parts algorithm. Subsequently, based on analytical expression, the performance of the presented strategy is theoretically analyzed via comparison with virtual inertia control, and the conclusion that the presented multi-segment droop control has better frequency regulation performance can be got. Furthermore, to achieve optimal frequency regulation performance, a Lagrangian function is established to determine the optimal parameters of the proposed control strategy. Finally, the performance of the proposed strategy was verified in a two-area system model constructed on MATLAB/Simulink. Results show that the proposed multi-segment droop control has better frequency regulation performance.
The novel hybrid advanced traction power supply device (NH-ATPSD), which consists of a traction transformer and a “two-phase-parallel-input to single-phase-cascaded-output” (2AC-AC) converter, has been proposed recently. It provides opportunities for solving the neutral section and negative-sequence power quality problems. However, different from the single-level power electronic device with cascade structure, the negative-sequence current and healthy module overload may occur when the input- or output-module fault occurs in NH-ATPSD. Thus, a dynamic fault-tolerant control for NH-ATPSD is proposed in this paper. For input module faults, the healthy module overload is avoided by the proposed dynamic modulation coefficient, which can dynamically adjust the power allocation between output port modules. In addition, the negative-sequence current is suppressed by controlling the partial power imbalance between the 2AC input modules. For output module faults, the active bypass of faulty module and increased voltage methods are adopted to keep the rated voltage and power output. Finally, the simulation and experiment results verify the effectiveness and efficiency of the proposed control strategy under different fault types.
典型运行场景提取对制定有效的日前运行策略具有重要意义.微电网中,可再生能源和新型负荷的强不确定性使得微电网的运行场景具有复杂时序特征.传统的场景聚类分析方法缺乏对时序特征的考虑,难以得到有效可信的典型运行场景.为此,文中提出一种基于深度时间聚类的微电网典型运行场景生成方法.首先,基于受路径约束的动态时间规整算法,量度时间序列的形态相似性;其次,设计了一种组合卷积神经网络和双向长短期记忆网络的时序自动编码器结构,提取复杂时序运行场景中的深层次特征并实现数据降维;然后,联合优化时序特征提取与时序聚类,得到有效、可信的典型运行场景;最后,提出考虑时间序列形态相似性的时间轮廓系数以及日内实际场景的运行成本作为聚类有效性评估指标.基于澳大利亚居民微电网的实际算例结果表明,与传统的场景聚类方法相比,所提方法具有更强的复杂时序特征挖掘能力,能够得到更具代表性的典型运行场景.
预留备用是应对电力系统强不确定性的必要举措,随着电力市场改革的不断推进,如何科学确定备用容量,并将备用费用在各责任方间公平合理地分摊是实现电力市场化改革的关键之一.针对负荷、新能源等不确定性,提出了备用容量估计及其成本分摊方法,根据不确定性预测误差的波动特征确定备用容量,并基于Vickrey-Clarke-Groves(VCG)理论合理分摊备用成本.首先,利用非参数核密度估计方法刻画新能源/负荷预测误差的概率密度曲线,无须假设新能源/负荷服从某一固定分布,并在此基础上提出基于蒙特卡洛法的备用需求场景模拟生成方法,确定备用总容量.然后,根据VCG理论,通过一个市场参与者(新能源/负荷)对其他市场参与者的替代效益进行价值量化,基于价值大小按比例分配备用成本到新能源/负荷一侧.最后,以修改的IEEE 30节点系统以及中国某省级电网661节点系统为例进行仿真分析,验证所提方法的有效性.
能源互联网技术推动了电力产消用户的规模化发展，产消者资源的优化运行与电力市场运营成为改善综合能效和投资收益的重要议题。产消用户的电力负荷精细化预测不但有益于提升分布式资源有限的容量价值，而且还能在售电侧市场全面放开时规避运营风险。首先，综述了产消者电力负荷预测技术及应用场景，提出了事件数据的含义并讨论了事件数据稀疏性带来的行为模式切变对于典型时序预测模型产生的极端预测误差问题。为避免解耦分析多元影响因素下的不确定性，构建了基于预测历史数据置信加权的短时预测修正模型，并分析了修正模型对于极限误差的收敛作用和经济性提升成效。最后，基于真实校园微电网工程运行数据验证了所提方法的有效性。
采用可行域投影方法实现电热能源系统间协调调度,是解决电力系统和供热系统行业信息壁垒的有效方法之一,而如何将系统内不确定性因素投影至边界信息并且开展协调决策是仍需解决的技术挑战.为此,文中提出供热系统鲁棒运行可行域投影概念及计算方法,并基于边界信息共享实现电热能源系统协调运行决策.首先,基于投影理论将供热系统内部运行数据信息投影至边界,构建供热系统运行可行域投影模型.在此基础上,考虑供热系统中外界环境温度及换热站热负荷不确定性,建立供热系统鲁棒运行可行域并将其投影至边界信息.然后,电力系统利用供热系统鲁棒运行可行域投影构建电热能源系统间协调决策模型,以实现电热能源系统协调调度.最后,通过算例验证所提供热系统鲁棒运行可行域投影模型及电热能源系统协调决策方法的必要性及准确性.
离岸海上风电制氢是中远海风力资源利用的重要方式,而分布式风电制氢机组由于无须集中汇流与大规模平台搭建,成为学界业界重点关注的技术路线.然而,受风场尾流效应影响,分布式风电制氢集群不同机组之间的运行状态相互耦合,制氢能力存在差异.文中提出考虑尾流效应的分布式风电制氢容量优化模型,基于机组协同控制对电解池容量空间分布进行优化配置.算例选取中国江苏省海域实际风源数据进行研究.首先,考虑尾流效应的风电制氢机组的协同控制可有效提高约3.05％的年期望制氢量.进一步,相比于电解池容量空间均匀分布方案,文中所得出的边缘大、内部小的最优容量空间配置方案可降低海上风电制氢的平准化制氢成本,验证了所提优化模型的有效性.
城市能源系统不仅需要具备高可靠性以应对小规模、大概率的日常故障事件，还需要具备高韧性以应对大规模、小概率的极端灾害事件。随着跨能源形式耦合以及电力电子化程度的不断提高，城市能源系统有望通过协调跨系统能量转移和海量电力电子设备快速调节提升系统韧性。首先，文中提出了极端灾害事件下城市能源系统两阶段韧性运行模型，综合考虑了电力电子设备快动态特性和多能源网络慢动态特性的建模与协调。其次，针对韧性模型存在多约束、求解复杂度高等问题，提出了基于稀疏权重斜决策树理论的数据驱动城市能源系统安全规则提取方法，将复杂的韧性模型转化为少量的混合整数线性约束，即安全规则，并内嵌至系统正常运行模型。最后，通过算例分析验证了所提方法的有效性及其相较于传统模型驱动方法在计算效率上的优势。
充分发挥流域梯级水电的调节作用,实现梯级水光系统的互补联合发电是促进清洁能源消纳的重要途径.文中考虑光伏出力不确定性,以整体可消纳电量期望最大为目标,提出了梯级水光互补系统的短期优化调度模型.该模型以机组为最小调度单位,精细化建模了电站约束、机组约束以及电网约束,通过梯级负荷在电站和时段间的合理调配,挖掘梯级水电的电网供电支撑和光伏互补协调双重作用,提升互补系统整体消纳水平.模型求解方面,采用分段线性逼近、引入0-1整数变量、发电水头离散等线性化方法和建模技巧处理模型中的非线性约束,将原模型转换为混合整数线性规划问题,并在Java环境中采用CPLEX工具实现求解.最后,以参考中国西南地区某流域梯级的4个水电站15台机组以及2个光伏群构建的互补系统为例,验证了所提模型和求解方法的有效性.
Multi-phase ring brushless exciter is widely used in million-kilowatt nuclear power plants at present. However, due to its lack of perfect relay protection, multiple faults on site have brought serious losses. The difficulty in implementing this protection lies in the fact that the exciter is a rotating-armature-type motor, and the only measurable quantity is the stator excitation current.Therefore, a single electrical characteristic is required to protect and distinguish various faults. Firstly, based on the characteristics of rotor armature current and spatial harmonic magnetic field before and after various faults, the fault characteristics and mechanism of exciter stator and rotor windings and rotating rectifier are deeply studied. According to the mutual induction relationship between stator and rotor currents in the asymmetric winding structure, the transient process and steady-state spectrum distribution characteristics and evolution laws of various faults are obtained. Secondly, taking the 11-phase ring brushless exciter as an example, the experiments and simulations with different faults are carried out on the prototype, and the experimental and simulation results verify the correctness of the theoretical analysis. Finally, a new protection principle based on stator excitation current is proposed. The prototype experiment and the field test results show that this protection method can not only realize reliable and sensitive protection from faults, but also distinguish the faults selectively.
传统电力系统与其他能源系统不断交叉融合,逐渐形成能源互联的新生态.在能源互联网中,数据使用权与数据所有权分离、信息资源与计算资源分离的特征使得多主体协同优化的隐私保护问题日益突出.文中从能源互联网协同优化的典型模式出发,总结了传统第三方代理计算模式及无第三方交互计算模式的隐私安全风险,提出了考虑隐私保护的能源互联网协同优化初步技术方案.首先,面向含第三方场景提出了基于信息伪装机制的安全代理计算方案,并研究了该方案的算法特性、算子构造方法以及基于云服务的用户侧、集群级、系统级应用场景.然后,面向无第三方场景提出了基于秘密分享原理的安全多方交互计算方案,并结合多中心化和全分布式两种应用架构,分析了该方案应用于海量主体或少量主体场景时的特性差异.最后,所述方案从数据隐私性和计算安全性层面,保障数据所有者的权益,遏制并降低能源互联网协同优化计算的数据泄露风险,实现可靠隐私保护.
为促进新能源的消纳利用,锂离子电池储能系统(LiBESS)在电网中得到了广泛应用,进一步导致电网故障特征更加复杂.为此,提出一种LiBESS电磁暂态建模方法.在分析故障特征的基础上,建立了功率变流器系统(PCS)模型和兼顾电池外特性、荷电状态的锂离子电池模型.PCS控制策略引入了故障穿越控制环和负序控制环,实现了故障穿越并消除了直流母线电压波动.此外,通过机理分析和仿真验证明确了LiBESS在不同充放电模式下的故障特性差异.最后,基于PSCAD/EMTDC的电磁暂态仿真和基于实时数字仿真器的硬件在环测试验证了所提建模方法的有效性.
随着电力市场改革的深化以及风电和太阳能为主的间歇性可再生能源发电(IREG)机组在电力系统中的占比不断升高,目前,对IREG机组采用的全额固定电价收购模式将按计划逐步终止,IREG机组将作为市场竞争主体参与电力市场,包括电力现货市场的运营.在此背景下,考虑绿色证书交易,通过建立三层决策模型优化政府对IREG机组的补贴政策,并引导其参与电力现货市场运营.首先,提出了过渡机制并建立了多市场多主体交易框架.然后,分别以求解最优合约覆盖率、社会效益最大化的市场出清和发电机组参与现货市场的最优投标策略为目标,建立了考虑绿色证书交易的多主体三层优化决策模型,并以市场出清结果作为这三层模型间的交互数据.接着,基于KKT(Karush-Kuhn-Tucker)条件,将该三层优化决策模型转化为混合整数线性规划模型,以提升求解效率.最后,通过算例对所提过渡机制的可行性和有效性进行了验证.
