Microgrid Dynamic Performance Improvement Using a Doubly Fed Induction Wind Generator

This paper describes a control approach applied on a doubly fed induction generator (DFIG) to provide both voltage and frequency regulation capabilities, and hence, an improvement in the dynamic behavior of a microgrid system. The microgrid system is assumed to be a portion of a medium voltage distribution feeder and is supplied by two distributed generation (DG) units, i.e., a gas-turbine synchronous generator and a variable-speed wind turbine with DFIG. A control approach algorithm is proposed for the DFIG unit to improve both voltage and primary frequency controls. Two distinct operation modes, i.e., grid-connected and islanding mode, are used in the proposed approach for proper transfer from normal to islanding operation. Case studies are simulated based on both planned and unplanned islanding scenarios to evaluate the performance of the control approach. The study results show that the proposed control approach for DGs in the microgrid increase the microgrid system's dynamic performance, reduce frequency changes, and improve bus voltages regulation during islanding and autonomous operations.      

基于三电平变流器的光伏微电网及其控制策略研究

孤岛运行的微电网常常具有可再生能源发电量时变、负载时变、三相不平衡等特点,为解决微电网的电能质量﹑稳定性等问题,本文提出适用于光伏微电网的三电平变流器结构及其电压内环,有功功率和无功功率调节为外环的控制策略。多机并联运行时,采用公共同步脉冲与均流解耦控制策略实现微电网全网范围内的变流器单机虚拟磁链的旋转同步。仿真和实验都证明了控制策略简单可行,电能性能指标比传统变流器优越,为四桥臂三电平双向变流器的开发提供理论基础、实验依据。     

微电网控制策略分析研究

为了能够对微电网不同运行模式下分布式电源进行协调控制,在分析单个微电源3种控制方式的基础上,研究了微电网的2种综合控制策略：主从控制策略和对等控制策略。为了验证2种不同的控制策略能使微电网可靠运行,对微电网在并网状态和孤岛状态下及二者状态切换的运行特性进行仿真。通过Matlab仿真,对微电网运行中各DG的有功无功功率、母线电压和系统频率曲线的变化规律进行了分析,并对2种不同控制策略的正确性与可行性进行比较。仿真结果表明,2种控制策略都能实现微电网可靠运行,对等控制策略的稳定性高,但其还有许多关键技术问题尚未解决,因而就目前来说,主从控制策略的实用性更强。     

基于等微增率法的混合微电网无功协调控制

在馈线潮流控制(FFC)和单元输出功率控制(UPC)两种控制模式下的混合微电网中,FFC模式下分布式电源(DG)的无功裕量不能满足增加的无功负载时,会引起微电网和大电网之间馈线无功潮流的变化,且馈线无功潮流值越大,脱网时公共连接点(PCC)电压偏差越大。为此,提出了一种考虑微电网内部节点电压稳定性的多台DG无功协调控制策略。该策略以FFC模式下DG为主要补偿设备,当不能满足负载需求时,采用等微增率法求解优化模型,从而确定UPC模式下DG无功输出参考值。算例结果表明,该控制策略能在维持微电网与大电网之间馈线无功潮流恒为最小值的同时,使得微电网内部节点电压更稳定。     

微电网孤岛模式下无功分配及电压优化分层控制策略

针对在微电网孤岛模式下并联运行的分布式电源采用传统下垂控制策略时存在无功功率受并网线路阻抗影响较大、电压偏离额定值等问题,提出了微电网孤岛模式下无功分配及电压优化分层控制策略,将微电网优化控制过程分为两层:初级控制层针对分布式电源无功功率受并网线路阻抗影响较大问题,提出变系数法下垂控制策略,根据下垂特性和线路特性约束方程调整下垂系数,实现无功功率精确分配;二级控制层应用多智能体一致性算法维持微电网电压稳定。仿真模型使用PSCAD/EMTDC搭建,结果表明,分层优化策略使无功功率合理分配的同时提高了微电网电压水平。     

基于随机森林分类的直流微电网孤岛检测

提出一种基于随机森林分类的直流微电网孤岛检测方法.该方法首先对原始数据进行清洗并提取特征,选择直流母线侧的电压、电流、输出有功功率及3者的一阶后向差分等6个孤岛特性指标作为检测特征,生成特征向量集,然后基于随机森林分类建立直流微电网的孤岛检测模型,实现了孤岛的准确检测,最后与决策树分类法进行比较,随机森林分类法在处理大...     

基于双模糊控制的独立微网能量优化策略

为使微网运行效益最大化,提出一种含风—储系统的独立微网的能量优化策略,该策略采用双层模糊控制方式,针对微网峰谷特性,根据日前启停机计划确定风电机组与需求侧管理负荷的投切状态,对实时调度则使用模糊控制得到风电机组、储能与负荷的功率值。对于微网瞬时功率波动,采用模糊理论,通过蓄电池—需求侧负荷混合系统平抑功率波动。实例应用结果表明,该独立微网能量优化策略有效。     

微电网中并列运行逆变器控制策略研究

考虑到微网内分布式电源的多样化和分散性,提出一种PQ控制与基于下垂特性的电压电流控制相结合的控制策略。PO控制可以实现间歇性微源的最大能源利用率,基于下垂特性的电压电流控制在微网运行模式或结构发生变化时,可以很好地实现负荷功率共享,以维持微网频率和电压的稳定。此控制策略既可以在并网模式下运行,也可以在孤岛模式下运行。并在PSCAD／EMTDC仿真平台上搭建了微电网仿真模型,验证了此控制策略的正确性和有效性。     

基于无源性的直流微电网并联变换器控制策略

针对可再生能源聚合而形成带混合负载的直流微电网稳定性与协调性问题,提出一种将无源控制与改进非线性干扰观测器前馈补偿相结合的新型控制算法,在消除恒功率负载对直流微电网的影响的同时提高了系统鲁棒性,再利用线路阻抗补偿来改善分流精度与实现电压无偏差。该文利用Matlab/Simulink搭建并联DC-DC变换器仿真模型进行验证,通过对比传统无源控制与比例积分调节的无源控制表明,提出的控制策略抑制了恒功率负载与线路阻抗对直流微电网的影响。最后,在Opal-RT半实物实验平台验证了该策略的有效性。     

交流微电网能量管理双层控制系统及其策略研究

为满足分布式电源和微电网技术发展的需要,针对含有光伏发电系统、风力发电系统、双馈风电模拟实验平台、储能系统以及负荷的微电网实验系统,设计开发了微电网能量管理双层控制系统,即本地智能控制层和专家协调控制层;分析了交流微电网在并/离网两种状态下的实时能量管理策略和锂电池储能系统经济运行模型;最后在该微电网实验系统主控单元中完成了对能量管理系统的调试,运行结果验证了所提能量管理策略的有效性和实用性。     

A novel sensorless current shaping control approach for SVPWM inverter with voltage disturbance rejection in a dc grid–based wind power generation system

A novel sensorless current shaping (CS) control strategy is proposed to avail better power quality (PQ) of a dc grid–based wind power generation system (WPGS) used on a poultry farm by generating an appropriate reference current for space vector pulse width modulation (SVPWM) inverter. The proposed CS strategy also offers adequate control for parallel operation of multiple generators and inverter applications, without requiring voltage and frequency synchronization. Further, to control the poultry farm–based WPGS, a two‐stage control loop is implemented such as energy flow control loop (EFCL) and harmonic control loop (HCL). The first loop is used to regulate the power flow, and the second loop is used to compensate harmonics. A mathematical current decomposition technique is suggested for an appropriate resistance emulation to realize a better power flow, higher harmonic rejection, and better inverter operation. In this planned approach for attaining constant wind speed, an electric ventilation fan in the poultry farm is used. A combined hybrid dc and ac grid approaches are suggested for facilitating variable load integration in a poultry farm–based microgrid system. Moreover, for achieving better power management during the islanded mode of operation, the battery energy storage (BES) device is integrated with the dc grid through a bidirectional converter. The proposed WPGS design and control approach has been simulated through MATLAB/Simulink software under various test conditions, to demonstrate the operational capability, to achieve better PQ, and to increase the flexibility and reliability in the microgrid operation.     

微网中储能系统的控制与分析

在微网系统中,大功率电力负荷的投切会导致电网电压幅值和频率产生波动。将储能装置应用于微网系统中,可以通过逆变控制单元,实时监控电网电压波动,即时调节配电网输送的有功、无功功率大小,从而达到平抑电网电压波动的效果。采用了电压频率环控制和有功、无功补偿控制相结合的控制算法,可以即时检测电网电压波动并进行快速补偿,具有较强的有功、无功调节能力。通过构建微网模拟环境,对比试验了不加储能装置和接入储能装置后微电网投入不同电力负荷时的电压波动情况,验证了控制策略的有效性和正确性。     

Microgrids formed by renewable energy integration into power grids pose electrical protection challenges

System parameters of a microgrid change in its two operating modes primarily due to output current limitation of PWM based inverters connected with renewable energy sources. The unavailability of an appropriate protection scheme, which must be compatible with both modes of a microgrid operation, is a major problem in the implementation of a microgrid. Two important properties of the microgrid components are peer-to-peer, and plug-and-play. It means that there is no component like a master controller which is critical for the operation of a system, and a distributed-generation unit can be installed at any location in a microgrid. These properties further complicate the protection of a microgrid. This paper reports the MATLAB/SIMULINK model of a microgrid along with the models of the conventional protection schemes and renewable energy distributed-generation resources. Malfunctioning in the conventional protection schemes in islanding mode is identified and models of newly proposed protection schemes are developed. Different types of faults are simulated in all the protection zones of the system and the system parameters are analysed to identify the possible fault detection methods. Based on the simulation results, a protection scheme is recommended that can meet the protection standards such as selectivity, co-ordination and reliability.     

基于改进型恒压控制与直流电压控制的交流微网协调控制方法研究

PQ控制、下垂控制与交流微网中光伏发电、风力发电等微电源之间存在协调性差问题,该文通过采用交流微网的直流电压控制策略,可使直流电压控制与光伏发电、风力发电之间的配合与协调更好,但当采用直流电压控制时,光伏发电、风力发电微电源的恒压控制策略就无法实现,为此改进恒压控制策略,提出基于改进型恒压控制与直流电压控制的交流微网的协调控制策略。Matlab/Simulink仿真结果验证了该文所提控制策略的有效性和可行性。     

微电网能量管理和控制简述

首先介绍了微电网的概念和微电网的基本结构以及运行方式。其次,给出了微电网能量管理系统的定义,分析了其与传统大电网的不同,并提出了其3种控制结构。在分析比较3种控制结构的优缺点之后,介绍了微电网能量优化调度的模型和算法以及能量管理的频率和电压控制策略。最后,提出了今后微电网能量管理系统可能采用的方法和频率电压控制的研究方向。     

Wind power smoothing using fuzzy logic pitch controller and energy capacitor system for improvement Micro-Grid performance in islanding mode

The need of reducing CO₂ emissions in electricity generation field for solving global warming problems has led to increase interest in Micro-Grid (MG) especially the one with renewable sources such as solar and wind generations. Wind speed fluctuations cause high fluctuations in output power of wind turbine which cause fluctuations in fr and voltages of the MG in the islanding mode and originate stability problems. In this study, a new fuzzy logic pitch controller and an energy storage ultra capacitor are proposed and developed to smooth the output power of wind turbine and enhance MG's performance in islanding mode. These two proposed controllers are compared with the conventional PI pitch controller, which is usually used to control wind generation system when the wind speed exceeds a rated value. Obtained results proved that our two proposed strategies are effective for the MG performance improvement during islanding mode. All models and controllers are developed using Matlab^® Simulink^® environment.     

考虑下垂控制策略的孤岛微网最优潮流

考虑到孤岛微网与传统大电网最优潮流的不同,提出一种基于下垂控制策略的孤岛微网最优潮流,构建了下垂控制分布式电源的孤岛微网模型,并建立了以系统发电成本最小和负荷能力最大为优化目标的孤岛微网最优潮流,同时利用模糊数学方法对多目标函数进行了处理,并以改进的33节点微网为例进行仿真模拟,利用最优潮流的经典计算方法——内点法对模型进行求解。结果表明,所提优化方法在求解孤岛微网最优潮流方面具有有效性和实用性。     

Enhancement of micro-grid performance during islanding mode using storage batteries and new fuzzy logic pitch angle controller

Power system deregulation, shortage of transmission capacities and needing to reduce green house gas have led to increase interesting in distributed generations (DGs) especially renewable sources. This study developed a complete model able to analysis and simulates in details the transient dynamic performance of the Micro-Grid (MG) during and subsequent islanding process. Wind speed fluctuations cause high fluctuations in output power of wind turbine which lead to fluctuations of frequency and voltages of the MG during the islanding mode. In this paper a new fuzzy logic pitch angle controller is proposed to smooth the output power of wind turbine to reduce MG frequency and voltage fluctuations during the islanding mode. The proposed fuzzy logic pitch controller is compared with the conventional PI pitch angle controller which usually used for wind turbine power control. Results proved the effectiveness of the proposed fuzzy controller in improvement of the MG performance. Also, this paper proposed using storage batteries technique to reduce the frequency deviation and fluctuations originated from wind power solar power fluctuations. Results indicate that the storage batteries technique is superior than fuzzy logic pitch controller in reducing frequency deviation, but with more expensive than the fuzzy controller. All models and controllers are built using Matlab® Simulink® environment.     

Accurate power sharing among multi-DG resources in a microgrid

In this paper, a sliding mode (SM)-based direct active and reactive power control for the distributed generations (DGs) in microgrid is presented. The grid-connected microgrid contains two three-phase DGs that are photovoltaic (PV) units, and three single-phase DGs consisting of fuel cell (FC), PV, and battery. In the proposed strategy, controlling of the active and reactive powers is carried out for the single-phase and three-phase DGs without any phase angle tracking of the network voltage or synchronization transformations. The proposed robust control strategy improves power sharing and regulates power components injected by the DGs, and it is tested under balanced and unbalanced loads.     

基于电储能的微电网控制关键技术研究及应用

可靠与先进的运行控制技术是微电网技术发展中重要的研究方向之一。对微电网控制技术热点之一的分层控制关键技术和研究现状做了系统介绍,从整体架构设计、各层控制方法技术特点及主要研究问题进行阐述。构建了一个MW级微电网并开展了关键控制技术研究与功能验证实践,开发了并网、孤岛、无缝切换和黑启动等功能,在试验过程中改进了基于储能的微电网并网运行和孤岛运行的优化逻辑,对并、离网切换和低电压穿越功能进行验证,展望了微电网协调控制的未来发展方向。