Overview of wind power intermittency impacts on power systems

Although integrating a large amount of wind power is technically possible, higher integration costs might be incurred when the penetration level of this intermittent power increases. This paper reviews wind power variability and its different impacts on power systems. In addition, an up-to-date overview of wind power balancing costs is presented.     

Probabilistic power quality indices for electric grids with increased penetration level of wind power generation

In future electric grids it is expected that the share of power produced by renewable energy systems will increase to supply large deficits in power demand. Wind energy is one of the most important sources of renewable energy generation systems. With increased penetration level of wind energy conversion systems in modern electric grid, the quality of power will inevitably be affected. Power quality (PQ) indices are used to quantify the quality of the power. They serve as the basis for comparing negative impacts of different disturbances on power networks. Previous research of PQ indices with electric grids including wind energy sources was mainly based on fixed wind speed. Therefore, the PQ indices were calculated as instantaneous values that do not reflect the overall power quality impact of the grid connected wind energy systems. The main objective of this paper is to propose new probabilistic PQ indices for electric grids including wind energy systems. The proposed PQ indices combine both the probabilistic nature of wind speed using discrete Markov analysis and the electric grid behavior. The main PQ indices proposed are those concerning harmonics, flicker, and voltage sag. The developed indices are suitable for electric grids that include high penetration level of wind based power sources. The method used is general and can be applied to other power quality indices or power system performance indices.     

Energy storage system-based power control for grid-connected wind power farm

Wind power is characterized as intermittent with stochastic fluctuations, which can result in deviation of grid frequency and voltage when the wind power ratio is high enough. These effects have a definite impact on stability and power quality of grid operation. This paper proposes an energy storage system (ESS) based power control for a grid-connected wind power system to improve power quality and stability of the power system. Vanadium redox flow battery (VRB), as an environmentally-friendly battery provided with many advantages, is employed in the ESS. A dynamic mathematical model of VRB is built by using an equivalent circuit, and its charging and discharging characteristics are analyzed. The VRB’s stable voltage is available in a wide range (around 20–80% state of charge), which is suitable for utilization of a single-stage AC/DC converter in the VRB-based ESS. With a proposed energy storage control method, VRB-based ESS is added at the exit of the grid-connected wind farm to filter fluctuations of wind power, which ensures that smooth power will be injected into the grid and which improves power quality of the power system. Simulations and experiments are carried out to verify the proposed power control method for these grid-connected wind power systems. The grid-connected wind farm with VRB-based ESS, wind speed (characterized as gust and stochastic wind), and wind turbines are modeled in simulations. Simulation results show that the grid-injected active power from the wind farm is effectively smoothed, and reactive power support can be provided for the grid by the designed VRB-based ESS. Experimental verification is achieved with a low power bench, where a RT-LAB real-time simulation platform and a direct torque controlled induction motor simulate a real wind turbine and a wind speed model is built in the RT-LAB real-time simulation platform. The experimental results verify the proposed scheme through demonstrating a stable and smooth power flow injected into the grid though the wind power fluctuated.     

基于两阶段随机优化建模的新能源电网灵活性资源边际成本构成的机理分析

针对大规模可再生能源并网给电力系统安全稳定运行造成的影响,考虑纳入燃气轮机储能等灵活性资源共同调节风电的波动性,构建了机组出力和备用容量联合优化的两阶段发电调度随机规划模型,并计及常规火电机组的多运行状态约束。然后,以模型中两阶段功率平衡约束对应的拉格朗日乘子分别作为日前和实时电价,从模型角度探究了边际成本构成机理。从灵活性资源供应的紧缺程度和灵活性资源需求的旺盛程度两个方面剖析灵活性资源的供需匹配对于系统边际电价的深层影响机理。算例结果说明了灵活性资源在应对风电不确定性和抑制尖峰电价的有效性,同时说明了多时间尺度的爬坡约束耦合、日前备用与实时出力调整量的耦合对于系统边际电价的影响。     

Impact of FACTS controllers on the stability of power systems connected with doubly fed induction generators

The increasing power demand has led to the growth of new technologies that play an integral role in shaping the future energy market. Keeping in view of the environmental constraints, grid connected wind turbines are promising in increasing system reliability. This paper presents the impact of FACTS controllers on the stability of power systems connected with wind energy conversion systems. The wind generator model considered is a variable speed doubly fed induction generator model. The stability assessment is made first for a three phase short circuit without FACTS controllers in the power network and then with the FACTS controllers. The dynamic simulation results yield information on (i) the impact of faults on the performance of induction generators/wind turbines, (ii) transient rating of the FACTS controllers for enhancement of rotor speed stability of induction generators and angle stability of synchronous generators. EUROSTAG is used for executing the dynamic simulations.     

Evaluating the Impacts of Real-Time Pricing on the Usage of Wind Generation

One of the impediments to large-scale use of wind generation within power systems is its nondispatchability and variable and uncertain real-time availability. Operating constraints on conventional generators such as minimum generation points, forbidden zones, and ramping limits as well as system constraints such as power flow limits and ancillary service requirements may force a system operator to curtail wind generation in order to ensure feasibility. Furthermore, the pattern of wind availability and electricity demand may not allow wind generation to be fully utilized in all hours. One solution to these issues, which could reduce these inflexibilities, is the use of real-time pricing (RTP) tariffs which can both smooth-out the diurnal load pattern in order to reduce the impact of binding unit operating and system constraints on wind utilization, and allow demand to increase in response to the availability of costless wind generation. We use and analyze a detailed unit commitment model of the Texas power system with different estimates of demand elasticities to demonstrate the potential increases in wind generation from implementing RTP.     

用神经网络对风力发电中电力电子故障分析

随着风能资源的利用水平不断提高,风力发电系统中的电力电子装置使用也越来越多,其工作可靠性要求也越来越高。风力发电装置多位于野外,为减轻检修人员的工作负担,对风机运行中远方检测到的大量数据进行快速而有效的可视化分类及故障状态粗略判断,引入了一种用单层前向神经网络来对数据进行快速分类绘制故障非故障分界线的方法。通过该方法能够很好地根据实时数据判断风机电力电子装置的故障。     

考虑风电随机性的微网多时间尺度能量优化调度

提出了考虑风电随机性的微网多时间尺度能量优化调度模型,实现了微网日前调度计划和实时调整之间的协调优化调度。该模型的日前调度部分以微网经济运行为目标,考虑风电出力的随机性,利用多场景方法提高了微网适应风电出力随机性的灵活性。在实时运行调整环节,利用响应速度较快的可控负荷消纳风电出力波动,使微网和外部电网的功率交换遵循日前调度计划,保证日前调度计划的有效性。该多时间尺度调度模型通过优化协调各种设备的运行,实现微网经济运行的同时,很好地消纳了风电随机性给外部电网带来的影响,实现了含风力发电微网对外部电网的可调度性。算例仿真验证了该模型的有效性。     

Electric vehicle integration into power systems

Sales of electric vehicle are rapidly growing worldwide. Vehicle grid integration is important for mitigating impact of charging demand on the distribution feeders, realizing renewable powered charging from the rooftop photovoltaic and wind power generation, and contributing to the Vehicle‐to‐Grid ancillary services for the power systems. This article reviews current trends of the vehicle grid integration R&D. Future prospective is also pointed out on the key issues such as an electrical interface, multiple services integration, and the electric vehicle living demonstration for open innovation.     

基于FPGA-CPU的双馈风电系统异步协同仿真

为实现双馈风电系统的并网及暂态实时仿真，研究了一种基于现场可编程门阵列(field programmable gate array, FPGA)与CPU协同仿真的多速率并行实时仿真方法。使用开关函数法对双馈风电系统中“背靠背”换流器建模并进行资源优化，基于PWM均值化原理完成不同步长系统之间的模型分割。利用FPGA运行速率高的优点，以200 ns的步长实现了“背靠背”换流器的小步长仿真。面向有源配电网实时仿真的需求，实现了FPGA与自主研发的实时仿真机(universal real-time experimental platform, UREP)的200 ns/50 并行协同仿真。通过与Simulink离线仿真结果对比，同时分析模型优化前后的FPGA资源消耗情况，验证了协同仿真的实时性与准确性，可为各类风电系统的并网及暂态研究提供技术参考。     

Multi-objective market clearing of electrical energy,spinning reserves and emission for wind-thermal power system

This paper proposes energy and spinning reserve market clearing mechanism for wind-thermal power system, including uncertainties in wind power generation and load demand forecasts. The impact of wind power and load demand volatility on the energy and spinning reserve market is taken into account. This paper considers reserve offers from the conventional thermal generators. The stochastic behavior of wind speed, and wind power is represented by Weibull probability density function (PDF), and the load demand uncertainty is represented by Normal PDF. This paper considers two objectives: energy and spinning reserves cost minimization, and emission minimization. The energy and spinning reserves cost minimization objective includes cost of energy provided by conventional thermal generators and wind generators, cost of reserves provided by conventional thermal generators. It also includes costs due to over-estimation and under-estimation of available wind power, and load demand. The proposed market clearing model provides a compromise solution by optimizing both the objectives simultaneously using multi-objective Strength Pareto Evolutionary Algorithm 2+ (SPEA 2+). The effectiveness of the proposed approach is established from the results on IEEE 30 bus system.     

考虑综合需求响应的电热系统调度

随着综合能源中电、热负荷不断增长以及热电联产(CHP)装置、风机等电源迅速发展,弃风现象愈发严重。为解决弃风问题,提出考虑电、热综合需求响应的优化模型。首先,在负荷侧分析电、热负荷的可调度价值,对电负荷建立实时电价模型,并采用价格型需求响应进行调整;其次,采用自回归滑动平均(ARMA)模型描述热负荷的传输延迟特性,并考虑模糊性供热舒适度,使得热负荷具有一定的弹性,即热力需求响应,通过2种响应模式对电、热负荷进行调整可增大风电上网空间;然后,在源侧增加电锅炉和储热装置,增加系统的灵活性,解耦CHP“以热定电”的刚性需求;最后,以系统的日运行费用与弃风成本最小为目标,在Matlab中调用CPLEX对模型进行求解。算例表明,所提方法可显著提升风电消纳能力,降低系统运行成本,提高能源利用效率。     

考虑日前小时电价的含风电电力系统调度模型研究简

为提高含大规模风电电力系统运行的灵活性,降低风电波动性对系统的影响和提高系统的风电接纳能力,在含风电电力系统调度中引入日前小时电价。基于考虑日前小时电价的风电最大接纳模式,建立了相应的数学模型和求解方法,以此为基础分析了引入日前小时电价模型在不同风电渗透率场景下对火电机组承担负荷、系统接纳风电能力和系统运行经济性的影响。算例分析表明,在含风电电力系统中引入日前小时电价能够缓解风电接入对电力系统的影响,提高系统的风电接纳能力与运行的经济性。     

Optimal power flow by a fuzzy based hybrid particle swarm optimization approach

This paper presents a fuzzy based hybrid particle swarm optimization (PSO) approach for solving the optimal power flow (OPF) problem with uncertainties. Wind energy systems are being considered in the study power systems. OPF is an optimization problem which minimizes the total thermal unit fuel cost, total emission, and total real power loss while satisfying physical and technical constraints on the network. When performing the OPF problem in conventional methods, the load demand and wind speed must be forecasted to prevent errors. However, actually there are always errors in these forecasted values. A characteristic feature of the proposed fuzzy based hybrid PSO method is that the forecast load demand and wind speed errors can be taken into account using fuzzy sets. Fuzzy set notations in the load demand, wind speed, total fuel cost, total emission, and total real power loss are developed to obtain the optimal setting under an uncertain environment. To demonstrate the effectiveness of the proposed method, the OPF problem is performed on the IEEE 30- and 118-Bus test systems.     

计及谷时段风电消纳的储能系统平抑风电功率波动控制策略

储能系统(energy storage system, ESS)仅参与平抑风电功率波动为单一场景的控制策略,存在ESS频繁充放电以及不能有效解决负荷低谷时段风电消纳等问题。为此,提出了一种计及谷时段风电消纳的ESS平抑风电功率波动控制策略。首先,根据风电特性与负荷需求的时序关系,确定ESS在一个周期内的充电和放电区间段。其次,提出了分区间控制的ESS控制策略,在充电区间段以平抑风电功率向上波动为目标存储电量;在放电区间段以平抑风电功率向下波动为目标释放电量。最后,考虑ESS的实时荷电状态(state of charge, SOC)和风电消纳,提出了基于模糊控制的ESS充放电功率修正方法。以某风电场实际数据为例,在风储联合发电系统仿真平台上进行了测试,验证了所提运行策略的可行性和优越性。     

考虑综合需求响应的电热系统优化调度

考虑配电网中电、热负荷的不断增长,以及热电联产装置(Combined heat and power,CHP)和风机等分布式电源的迅速发展,提出考虑电、热综合需求响应的优化模型。首先,在负荷侧分析电负荷和热负荷的可调价值,电负荷建立实时电价模型,采用价格型需求响应进行调整；热负荷是考虑热负荷的传输延迟特性,采用自回归滑动平均(ARMA)模型描述和计及模糊性供热舒适度特性,使得热负荷具有一定的弹性,即热力需求响应,通过这两种响应模式对电、热负荷进行调整,增大风电上网的空间；其次在源侧增加电锅炉和储热装置,增加系统的灵活性,解耦CHP“以热定电”的刚性需求,最后以系统的日运行费用与弃风成本最小为目标,在Matlab中调用CPLEX对模型进行求解。算例结果表明,在源侧采用CHP+电锅炉和储热相比于传统的CHP+储热,风电的消纳能力有显著提升；在荷侧考虑电、热综合需求响应相比于传统的考虑单一需求响应,可有效的降低系统的运行成本,提高能源的利用效率。     

Identifying the optimum wind capacity for a power system with interconnection lines

This paper presents a general framework for identifying the optimum wind capacity to be integrated in a power system with interconnection lines. Wind generation is treated as negative demand, together with the load demand, which must be covered by the conventional power generation and the energy interchange with neighboring systems. Under the presumption that the time-varying wind and load together with the trading price with neighboring systems could be statistically modeled by specified probability distributions, a chance constrained programming (CCP) model is formulated to address the wind capacity planning problem. The objective is to maximize the yearly net profit of the entire power system subject to the operational constraints and the reliability requirement. Wind power curtailment and load shedding are allowed to improve the system flexibility but incur penalty costs. The optimization problem is solved using a hybrid intelligence algorithm incorporating Monte Carlo simulations, a neural network and a genetic algorithm. The feasibility of the proposed approach is verified by a case study on a given power system.     

含大规模风电的电力系统小扰动稳定研究综述

针对风电并网对电力系统带来的小扰动稳定性问题,从对小扰动稳定性的影响和风机附加阻尼控制两方面对该领域的最新进展进行了综述。简述了小扰动稳定性的相关概念,介绍了风电机组的类型和模式。将目前的研究方法归纳为两类:基于确定性方法和概率分析方法,并分析指出了不同类型的风电机组对小扰动稳定性的影响及存在的问题。综合讨论了风机附加阻尼控制器提高系统阻尼的方法,提出了该领域需进一步开展的工作。     

基于虚拟仪器技术的 风电场电能质量监测系统

大规模风电并网对电力系统的电能质量影响较大,需要对风电场的电能质量给出全面准确的分析。提出了一种基于虚拟仪器技术的风电场电能质量实时监测系统。该系统以信号调理电路为硬件基础,以USB接口采集卡为核心,以Lab VIEW为软件开发工具。具有波形显示、数据读取、信号分析、基于国标判断等功能,可以对风电场的电能质量进行全方位监测,对风电场发出的电能质量是否适合并入电网进行判断。     

江苏沿海风电场接入系统后影响分析

描述了目前江苏沿海地区风电的概况,并对风电并网的一些技术原则作了介绍,最后具体分析了江苏沿海风电并网之后对电网电源侧及电网侧所带来的相关影响,包括电能质量、短路电流等。江苏沿海大规模开发风力发电,能够基本符合电力供需平衡的发展需要。