Performance of PI controller for control of active and reactive power in DFIG operating in a grid-connected variable speed wind energy conversion system

Due to several factors, wind energy becomes an essential type of electricity generation. The share of this type of energy in the network is becoming increasingly important. The objective of this work is to present the modeling and control strategy of a grid connected wind power generation scheme using a doubly fed induction generator （DFIG） driven by the rotor. This paper is to present the complete modeling and simulation of a wind turbine driven DFIG in the second mode of operating （the wind turbine pitch control is deactivated）. It will introduce the vector control, which makes it possible to control independently the active and reactive power exchanged between the stator of the generator and the grid, based on vector control concept （with stator flux or voltage orientation） with classical PI controllers. Various simula- tion tests are conducted to observe the system behavior and evaluate the performance of the control for some optimization criteria （energy efficiency and the robustness of the control）. It is also interesting to play on the quality of electric power by controlling the reactive power exchanged with the grid, which will facilitate making a local correction of power factor.

High performance decoupled active and reactive power control for three-phase grid-tied inverters using model predictive control

Finite control set-model predictive control (FCS-MPC) is employed in this paper to control the operation of a three-phase grid-connected string inverter based on a direct PQ control scheme. The main objective is to achieve high-performance decoupled control of the active and reactive powers injected to the grid from distributed energy resources (DER).The FCS-MPC scheme instantaneously searches for and applies the optimum inverter switching state that can achieve certain goals, such as minimum deviation between reference and actual power;so that both power components (P and Q) are well controlled to their reference values.In addition, an effective method to attenuate undesired cross coupling between the P and Q control loops, which occurs only during transient operation, is investigated. The proposed method is based on the variation of the weight factors of the terms of the FCS-MPC cost function, so a higher weight factor is assigned to the cost function term that is exposed to greater disturbance. Empirical formulae of optimum weight factors as functions of the reference active and reactive power signals are proposed and mathematically derived. The investigated FCS-MPC control scheme is incorporated with the LVRT function to support the grid voltage in fulfilling and accomplishing the up-to-date grid codes. The LVRT algorithm is based on a modification of the references of active and reactive powers as functions of the instantaneous grid voltage such that suitable values of P and Q are injected to the grid during voltage sag.The performance of the elaborated FCS-MPC PQ scheme is studied under various operating scenarios, including steady-state and transient conditions. Results demonstrate the validity and effectiveness of the proposed scheme with regard to the achievement of high-performance operation and quick response of grid-tied inverters during normal and fault modes.

ADMM-based Distributed Active and Reactive Power Control for Regional AC Power Grid with Wind Farms

A distributed active and reactive power control(DARPC)strategy based on the alternating direction method of multipliers(ADMM)is proposed for regional AC transmission system(TS)with wind farms(WFs).The proposed DARPC strategy optimizes the power distribution among the WFs to minimize the power losses of the AC TS while tracking the active power reference from the transmission system operator(TSO),and minimizes the voltage deviation of the buses inside the WF from the rated voltage as well as the power losses of the WF collection system.The optimal power flow(OPF)of the TS is relaxed by using the semidefinite programming(SDP)relaxation while the branch flow model is used to model the WF collection system.In the DARPC strategy,the large-scale strongly-coupled optimization problem is decomposed by using the ADMM,which is solved in the regional TS controller and WF controllers in parallel without loss of the global optimality.The boundary information is exchanged between the regional TS controller and WF controllers.Compared with the conventional OPF method of the TS with WFs,the optimality and accuracy of the system operation can be improved.Moreover,the proposed strategy efficiently reduces the computation burden of the TS controller and eliminates the need of a central controller.The protection of the information privacy can be enhanced.A modified IEEE 9-bus system with two WFs consisting of 64 wind turbines(WTs)is used to validate the proposed DARPC strategy.

Research on On-Line Coordinated Control Strategy to Improve the Voltage Vulnerability after Disturbance

The on-line coordinated control strategy among multi-voltage controls is important to keep voltage security in post-fault systems. Based on the wide area measuring information, the energy function, which can qualify the impacts of the different control actions on voltage of different nodes, is proposed. And then, considering the impacts of different control actions on the node voltage being treated as a weight matrix, the energy margin is used as the objective function and the reactive power margin is innovatively used as the constraint to regulate the control actions globally according to the weight values. At last, the objective functions are solved to get the optimal global coordinated control strategies. The proposed method is identified in an IEEE-30 Bus system and the simulation results show that it effectively improves the voltage stability.

基于数据驱动的配电网无功优化

传统无功电压控制由于分布式电源、储能以及柔性负荷的接入面临计算速度和精度上的挑战。该文提出了一种基于数据驱动的配电网无功电压优化方法,通过跟踪实际系统的运行参数,实现无功电压的主动控制。在极限学习机中引入自动编码器构建深度学习机制,利用自动编码器建立极限学习机输入-输出的直接耦合关系,实现无监督学习和有监督学习有机结合,缩短训练模型的迭代过程;利用蒙特卡洛法基于分布式电源、负荷预测信息构建配电网运行场景,利用深度极限学习机挖掘运行场景优化运行与无功调压设备状态间的内在联系,建立电网运行场景与系统无功调压策略的映射关系。该文提出的基于数据驱动的无功优化方法不依赖实际系统潮流计算,能够实现配电网运行状态的跟踪和无功调节设备的优化调度,为配电网无功电压的主动控制打下基础。

有源前端组网的直流船舶电网高能效运行控制

直流船舶电网为航运业绿色转型提供了有效可行的解决方案。考虑到实际船舶的运行工况,本文提出一种分层协调控制策略,主要用于有源前端组网的直流船舶电网中功率单元协调运行的设备层控制系统和功率层控制系统。其中,设备层控制系统负责实现发电机组转速的无静差跟随与不同容量柴油发电机组间的动态/稳态功率共享;功率层控制系统负责提升母线电压质量,提高系统能效。最后,利用仿真与半实物仿真系统对控制策略进行验证,结果表明该控制策略可有效提高系统运行能效,最高节省约10%的燃油。

基于“先无功–后有功”功率补偿的配电网电压协同控制策略

整县分布式光伏电源的大量开发与利用及分布式电源规模化并网对实现“碳达峰、碳中和”与“乡村振兴”两大国家战略具有重要的现实意义。由于分布式电源发电尖峰和低谷阶段与负荷峰谷时常不同步,进而导致配电系统过/欠电压问题,严重影响了电能质量,甚至威胁系统安全。针对上述问题,本文提出一种基于“先无功–后有功”功率补偿的配电网层级式电压协同控制策略。首先,建立基于“先无功–后有功”功率补偿的配电网层级式电压协同控制框架。其次,结合多微电网节点注入电流与电压的方程与功率–电压灵敏度分析,根据多节点电压越限程度,提出一种基于“先无功–后有功”功率补偿的多智能体协同调节策略,该策略先通过无功补偿器进行无功调节,当电压尚未得到有效治理时,再采用多微电网进行有功调节。再次,为了进一步满足各节点微电网有功功率调节需求,并考虑电网内部源–荷–储运行成本与污染排放,提出一种基于多目标优化的微电网内部分布式源–荷–储优化协调功率控制策略。最后,在MATLAB平台中设计了3种仿真场景以及IEEE测试系统模型对所提控制策略进行了验证。结果表明,所提出的电压协同控制方法在最经济的情况下可以实现各节点电压的综合高效治理,同时,所提出的微电网优化协调功率控制策略能使源–荷–储在绿色经济的供电模式下实时精准地满足电压治理目标下微电网有功调节的需求。仿真实验结果验证了本文所提控制策略的有效性。

Intelligent Assessment of Active and ReactivePower Flow with Satisfying Accuracy forN-k_(1)-k_(2) Cascading Outages

Addressed to the N-k_(1)-k_(2) cascading outages,it is computationally burdensome for the reliable calculation of active and reactive power flows.This paper builds a comprehensive framework with three algorithms,including the distribution factor(DF),the Newton-Raphson(NR),and the first iteration of NR algorithm(termed as 1J).Classifiers are designed to determine whether the NR algorithm should be employed for accuracy.Classifier features are extracted upon the analytical error of 1J.As reactive power is partially considered in the 1J but neglected in the DF algorithm,the deviation between the solutions is taken as one crucial feature.The support vector machine(SVM)is then utilized for classifier training.As the deep integration of the causal inference and the statistical paradigm,this framework calculates active and reactive power flows rapidly,reliably,and robustly.The effectiveness and robustness are fully validated in three typical IEEE systems.

Vibration control of the finite L-shaped beam structures based on the active and reactive power flow

This paper analyzes the physical meaning of the active and reactive power flow in the finite L-shaped beams and studies the active vibration control of the structures based on the active and reactive power flow.The traveling wave approach is used to calculate the structural dynamic responses.Because the error of control force is inevitable in practical applications,the effects of the error of control force on the control results are studied.The study indicates that the error of control force has pronounced influence on the control results of the acceleration and reactive power flow.It is obvious that the reactive power flow can represent the vibration strength component of the complex intensity,and the active power flow strongly depends on the structural damping of the finite beams.

基于安全强化学习的主动配电网有功-无功协调优化调度

提出一种基于离线策略的安全强化学习方法,通过离线训练大量配电网历史运行数据,摆脱了传统优化方法对完备且准确模型的依赖。首先,结合配电网络参数信息,建立了基于约束马尔可夫决策过程的有功无功优化模型;其次,基于原始对偶优化法设计了新型安全强化学习方法,该方法在最大化未来折扣奖励的同时最小化成本函数;最后,在配电系统上进行仿真。仿真结果表明:所提方法能够根据配电网实时观测信息,在线生成满足复杂约束条件且具有经济效益的调度策略。

面向大容量风电并网的VSC-MTDC功率协调控制

基于电压源换流站的多端直流输电(VSC-MTDC)已成为大容量风电远距离传输并网的首要选择。针对含大规模风电场的VSC-MTDC系统的功率协调控制策略进行了深入研究。首先,分析大规模风电并网时下垂系数对有功功率分配的影响,指出采用固定下垂系数存在优先级电网功率缺额的可能性和缺乏有功功率分配灵活性等问题。然后,针对此类问题,提出一种基于主从控制与自适应下垂控制相结合的功率协调控制策略,该策略根据风电功率情况制定3种控制模式,从而实现风电功率灵活分配。最后,在MATLAB/Simulink上构建了风电并网的四端柔性直流输电系统,仿真结果验证了所提控制策略的可行性和有效性。

构网型逆变器与SVG并联系统无功功率协调控制策略

以静止无功发生器(static var generator,SVG)为例,针对构网型逆变器和SVG并联系统的电压稳定性问题,提出构网型逆变器与SVG并联系统无功功率协调控制策略。将并联系统的运行状态总结为四种工况,通过工况识别、无功补偿量计算、无功功率分配策略、工况切换,来协调不同工况下构网型逆变器与SVG注入公共耦合点的无功功率,使并联系统在各种情况下均可稳定可靠工作。在MATLAB中搭建模型并进行仿真,结果表明所提控制策略可以实现工况的快速识别与切换、无功补偿量的计算、无功功率的分配,以及对公共耦合点电压的快速支撑。

直接电压控制构网型变流器控制参数暂态稳定影响分析

目前针对直接电压控制构网型变流器暂态失稳模式的演化和控制参数对暂态稳定的影响机理尚需进一步深入研究。首先,分析了两种常见电流限幅策略对变流器暂态稳定性的影响,归纳总结出3种暂态失稳演化路径。其次,通过极限切除时间、极限切除角揭示了变流器有功环节不同参数对暂态稳定的影响规律,并针对直接电压控制构网型变流器的内电势和并网点电压之间的非线性关系,使用变流器临界势能为指标,揭示了变流器无功环节不同参数对稳定性的影响规律。在此基础上,解释了不同控制环节参数对变流器暂态稳定性的影响出现反常规律的机理。最后,在PSCAD仿真平台上通过算例验证了理论分析的正确性。

高比例光伏接入的配电网分布式运行优化技术

高渗透率光伏和储能并网的现代配电网具有规模庞大、设备众多、运行工况复杂多变的特点,传统的集中式优化方法不再适用。与此同时,有载调压变压器、并联电容器等均为传统离散设备,导致配电网有功无功功率协调优化模型呈现非凸特性,而当前通用分布式算法仅适用于求解凸模型。为解决该问题,提出了计及模型非凸特性的配电网分布式有功无功功率协调优化方法。以提高配电网运行经济性为目标,利用随机规划理论进行光伏有功功率不确定性刻画,建立配电网分布式随机有功无功功率协调优化模型。针对所建模型的非凸特性提出基于交替寻优过程的分布式算法,实现该模型可靠求解。最后通过PG&E69节点系统进行算例分析,验证了所提分布式有功无功功率协调优化方法的有效性以及分布式算法的可靠性。

高压级联SVG电流PR控制策略

对SVG在出现无功阶跃扰动时的补偿控制进行深入研究。SVG在无功功率调节时,如果出现阶跃扰动,无功功率的调节会直接影响有功功率的调节,这是因为传统的旋转坐标系控制方法对于有功功率和无功功率的控制环路之间存在耦合关系。为此,文中引入了有功和无功的解耦控制。另外,无功的阶跃信号会引起直流母线电压的突变,故将直流分量引入装置侧输出电流的值,并将这个直流分量滤除,保证控制的稳定性。最后在仿真的基础上,以光伏电站为背景对所提方法进行现场验证,结果充分证明了该算法的有效性。

考虑新能源不确定出力的有功无功协调降损控制策略研究

在高比例新能源接入电力系统的背景下,电网安全、经济的运行面临着巨大挑战。该文考虑风光出力的不确定性,建立有功无功协调优化的多目标优化模型。运用拉丁超立方抽样(latin hypercube sampling,LHS)场景生成法和Kantorovich距离的场景缩减技术,得到典型日的风电和光伏出力;建立以系统运行有功网损和电压偏移最小的多目标综合优化调度模型,采用传统的鲸鱼优化算法(whale optimization algorithm,WOA)与粒子群优化(particle swarm optimization,PSO)相结合的鲸鱼群(WOA-PSO)算法求解该模型,得到Pareto解的分布;根据优化结果制定无功补偿装置的投切功率以及储能系统充放电策略,达到提升系统电压稳定性与平缓新能源出力波动的效果,减少功率在线路上的损耗,实现电网的安全、节能运行;在改进IEEE30节点系统上进行实验分析,验证所提模型与求解算法的有效性与合理性。

基于自抗扰控制的双馈风电场分层无功功率支撑策略

随着风力发电的规模化联网,电力系统电压问题愈发突出。为提高双馈风电场在电网故障下的暂态响应特性,提出1种基于自抗扰控制(ADRC)的双馈风电场分层无功功率支撑策略。首先,描述了双馈异步风力发电机(DFIG)的无功功率边界;其次,设计双馈风电场的分层无功功率支撑策略,在场站控制器中利用自抗扰控制器产生电压控制信号,在机组控制器中采用变增益系数辅助调整电压;最后,使用Washout滤波器抑制暂态过电压,搭建基于EMTP-RV的双馈风电场仿真模型。仿真分析表明,所提控制策略在电网电压跌落时具有良好的支撑效果。

基于电气自动化的无功补偿装置在电源系统中的协调控制研究

电源系统中,无功功率的产生会导致电压波动、线损增加、电能质量下降,为有效提升电源系统的稳定性,减少人工劳动强度,增加电力运行的安全性,文章对基于电气自动化的无功补偿装置在电源系统中的协调控制进行研究,在深入了解无功补偿原理的基础上提出一种固定补偿和动态补偿相结合的智能化无功补偿方式,实现电源系统的协调和控制。该种方式有效解决了有功功率波动和无功补偿的问题,在降低有功网损的同时降低了电源运行成本,实现了经济效益和技术效益的双重提升。

调相机交流母线电压无功双闭环控制策略及母线电容协调控制研究

针对高压换流站调相机无功补偿过程中出现的功率超调与交流母线电压大幅波动,考虑无功功率扰动的影响,提出一种交流母线电压外环、调相机无功内环的双闭环调相机先进控制方法,该控制方法在保证调相机快速响应交流母线电压波动的同时能够有效抑制无功功率超调。为了进一步抑制无功功率波动导致的高压换流站交流母线电压的大幅波动,通过电容串接吸收电阻的方式,设计一种调相机与交流母线电容无功补偿协调控制策略,提升高压换流站的稳态与动态性能。通过PSCAD软件验证了所提控制方法的正确性与有效性。

Optimal Active Power Dispatching of Microgrid and Distribution Network Based on Model Predictive Control

First, a three-tier coordinated scheduling system consisting of a distribution network dispatch layer, a microgrid centralized control layer, and local control layer in the energy internet is proposed. The multi-time scale optimal scheduling of the microgrid based on Model Predictive Control（MPC） is then studied, and the optimized genetic algorithm and the microgrid multi-time rolling optimization strategy are used to optimize the datahead scheduling phase and the intra-day optimization phase. Next, based on the three-tier coordinated scheduling architecture, the operation loss model of the distribution network is solved using the improved branch current forward-generation method and the genetic algorithm. The optimal scheduling of the distribution network layer is then completed. Finally, the simulation examples are used to compare and verify the validity of the method.