交流微电网系统并网保护分析

交流微电网系统保护按其功能可分为并网保护和微电网内部保护。文中以交流微电网的结构和特点为基础,重点分析不同规模微电网并网保护,参照微电网类型将其分为系统并网保护、区域并网保护及单元并网保护。通过对不同级别微电网负荷、运行方式进行分析,结合各级微电网的功能,提出3种类型并网保护的配置策略。考虑到大型微电网结构复杂,不同级别微电网之间可能存在包含关系,分析了发生区内、区外故障时3种类型并网保护之间动作时间的配合。最后在PSCAD/EMTDC中建立IEEE P1547.4典型微电网拓扑,仿真验证了并网保护配置方案的有效性与可行性。     

微电网群特征分析及示范工程设计

随着更多的分布式电源接入,微电网及其群落出现在配电网末端。如何合理规划设计微电网及其群落成为智能电网发展必须解决的关键问题之一。从运营模式和技术形态2个方面阐述微电网群的主要特征,比较微电网群与其他分布式电源接入配电网技术解决方案的区别。接着,提出微电网群的一般规划设计流程。在此基础上,结合广西猫儿山地区的实际供电需求和条件,完成了猫儿山微电网群示范工程的方案设计,并对其合作运营模式成立的条件进行校验。研究工作拓展了微电网群的实际应用,可为微电网群相关规划设计和运行管理提供借鉴依据。     

微电网规划关键问题与运行仿真

微电网的合理规划是实现其效益的基础。本文从负荷预测、接入方式、电压等级和容量以及网架结构4个方面对微电网规划的关键问题进行研究。利用电磁暂态仿真软件EMTDC/PSCAD建立了含微型燃气轮机、风力发电机、光伏电池等分布式电源的微电网模型及其控制模型,对微电网运行模式切换后功率变化、频率稳定性、电压稳定性等运行情况进行仿真。实验表明,上述规划方法对工程实践具有一定的指导作用。     

微电网相关问题及技术研究

介绍了分布式电源微电网的技术特点。详细分析了分布式电源接入形成的微电网对电压、频率和谐波的影响,并提出了相应的技术措施。根据微电网可以并网和孤岛运行的特性,对已有控制方法进行分类并详细介绍其控制策略及优缺点。针对分布式电源对微电网保护的影响,介绍了适用于微电网保护的新方法。最后对微电网其他研究方向进行了探讨。     

微电网相关问题及技术研究

介绍了分布式电源微电网的技术特点.详细分析了分布式电源接入形成的微电网对电压、频率和谐波的影响,并提出了相应的技术措施.根据微电网可以并网和孤岛运行的特性,对已有控制方法进行分类并详细介绍其控制策略及优缺点.针对分布式电源对微电网保护的影响,介绍了适用于微电网保护的新方法.最后对微电网其他研究方向进行了探讨.     

微电网保护策略综述

近年来为提高电能质量和供电可靠性,越来越多的微电网接入配电网。微电网由分布式电源、储能装置和可控负荷组成。微电网的引入带来的一个主要挑战是设计在并网和孤岛2种运行模式下均能有效保护微电网的保护策略。总结了微电网继电保护面临的难点和特殊需求,介绍了微电网保护的研究现状,探讨了不同方案的优缺点,并给出了未来微电网保护的一些建议。     

微电网规划研究综述

为了解决分布式电源直接接入电网带来的诸多问题、同时充分发挥分布式电源的效能,一种有效的方法是将分布式电源以微电网的形式接入电网。介绍了美国电气可靠性技术协会提出的微电网概念,综述了不同形式的微电网结构,并研究了微电网的规划体系和规划算法。最后在此基础上,重点分析了微电网规划中待研究或研究较少的问题,为微电网规划及相关课题的研究奠定基础。     

微电网运行与发展研究

微电网可以减缓传统电力系统扩张的需求,控制潜在的数量庞大的分布式电源(DERs)带来的新挑战,并能满足用户对高级别的安全性和电能质量的需求。详细阐述了微电网的概念和结构,介绍了世界各地微电网研究现状,并在此基础上结合中国国情,分析了微电网在中国的发展,并提出了几点建议。     

微电网控制技术的研究现状及发展方向

提出微电网作为大电网的有益补充,已经成为众多国家解决电力系统安全性和可靠性问题的重要辅助手段。就微电网的研究现状特别是其控制技术进行了深入分析,基于目前已有的三类微电网经典控制方法,分析了并网和孤网两种不同运行模式下的控制策略,并对微电网研究中存在的问题和未来研究方向进行了探讨。     

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。     

Rural electrification and expansion planning of off-grid microgrids

This paper presents the past and current practices for rural electrification and the current trend in using off-grid microgrids to provide energy to the customers with no access to the central electricity network. The challenges correspond to the capacity expansion of off-grid microgrids including the financial and business models for establishing these technologies, the economic and reliability considerations, the environmental issues, the expansion and feasibility studies, and the uncertainties in the operation horizon were presented.     

低压直流微电网新型主动限流器及控制策略

低压直流微电网中直流母线发生短路故障后,现有的被动式保护措施难以有效保护电力电子装置,并且当计及直流线路电感与变流器直流母线侧电容时,常规主动限流器会出现限流电感电流振荡的特性。详细分析了该电流振荡特性产生的机理,探究了系统参数变化对限流电感电流振荡峰值的影响。并提出了一种新型主动限流器拓扑结构及控制策略,该拓扑结构通过增加能量耗散支路,在限流器直流母线侧电容电压产生负压时导通,以此耗散能量,解决了电感电流振荡的问题。通过仿真与实验,验证了所提新型主动限流器对电感电流振荡特性抑制的有效性,且在不同工况下具有良好的鲁棒性。     

A systematic review of robust control strategies in DC microgrids

This paper provides a comprehensive and systematic review of robust control strategies in DC microgrids. Microgrids gain worldwide attention in decades regarding its effective and feasible integration of distributed generations (DGs). Getting rid of frequency synchronization and reactive power problem, the DC microgrid is superior to its ac counterparts in stability, flexibility and complexity. The recent efforts were mainly directed toward developing the feasibility of implementing DC microgrids on kinds of specific application scenarios. DC microgrids design-related aspects such as the system architecture and topology, voltage levels, operation and control framework, stability analysis method, and protection challenge have been studied in a deep degree. In this paper, operation and control framework in both grid-connected (grid-forming) mode and islanding (grid-following) mode will be focused, to provide the guideline where we currently stand on the migration path from the overwhelming fully AC microgrids to a more flexible DC microgrids. Besides, the impediments against stability and effectiveness of DC microgrids and representatively proposed solutions will be discussed.     

微电网并网标准研究

根据现有的国内外相关标准和规范,从电力系统的角度初步研究了微电网并网、并网运行以及解列过程的技术要求。提出了微电网并网的基本要求和并网准则,基于配电网可靠性考虑,对微电网并网时接入点、接入容量和接入方式提出了要求。对微电网接入电网引起的电能质量、有功功率和无功功率控制、电压调节、继电保护、通信、监测和电能计量等问题进行了分析。将微电网的解列分为正常解列和事故解列,着重强调事故解列时孤岛区域的划分原则及解列要求。通过对微电网接入电网所需考虑的关键问题进行分析探讨,为制定微电网的接入标准提供了一定的基础。     

Distributed cooperative synchronization strategy for multi-bus microgrids

Microgrids can operate in both grid-connected mode and islanded mode. In order to smooth transfer from islanded mode to grid-connected mode, it is necessary to synchronize the point of common coupling (PCC) with main utility grid (UG) in voltage frequency, phase and amplitude. Conventional synchronization methods based on centralized communication are very costly and not suitable for multi-bus microgrids that have a large number of distributed generators (DGs). To address this concern, this study presents an active synchronization control strategy based on distributed cooperation technology for multi-bus microgrids. The proposed method can reconnect the microgrid in island to UG seamlessly with sparse communication channels. Synchronization correction signals are generated by a voltage controller, which are only transmitted to the leader DGs. Meanwhile, each DG exchanges information with its neighbors. Finally, the voltage of PCC will synchronize with the main grid and all DGs will achieve the consensus behaviors. Compared with traditional synchronization methods, the proposed method does not need complex communication networks and improves flexibility and redundancy. Even if the distributed communication breaks down, the primary droop control can still operate robustly. Small signal model of entire system is developed to adjust the parameters of distributed active synchronization controller. Simulation results are presented to verify the effectiveness of the proposed method.     

基于生存性评估的含微电网的保底电网网架构建方法

微电网具有较强的灵活性、可靠性和可控性,将微电网应用于保底电网能够增强城市核心区域的安全供电、抵抗灾害和快速复电能力。但是,由于组成元件和运行目标的不同,现有规划方法无法适用于含微电网的保底电网。为此,提出了一种基于生存性评估的含微电网的保底电网网架构建方法。计及了微电网对保底电网运行的影响,提出了配电网支路和节点的重要性评估指标。构建了兼顾抵抗性、安全性和恢复性的含微电网的保底电网生存性指标体系,建立了含微电网的保底电网网架搜索模型。算例分析表明,所提方法能够保证在严重自然灾害下重要负荷的持续供电和保底电网的安全运行以及提高保底电网的快速复电能力。     

孤岛微电网的分布式有限时间事件触发二次协调控制

针对传统的下垂控制策略会导致孤岛微电网稳态角频率和电压偏离额定值,且其依赖周期性通信的问题,提出一种孤岛微电网的分布式有限时间事件触发二次协调控制.首先基于多智能体系统的追踪一致性,即以系统稳态电压和角频率参考值为虚拟领航者,视分布式电源(DG)为多智能体系统的智能体,来实现系统电压和角频率的恢复控制以及期望的有功功率比例分配.然后设计了分布式有限时间事件触发二次协调控制,且只在事件触发时刻进行信息交换,其余时刻利用状态估计器输出代替DG实际状态.采用李雅普诺夫方法分析了所提策略的稳定性和可行性.最后在MATLAB/Simulink中搭建孤岛微电网测试系统进行仿真分析,仿真结果及理论分析验证了所提控制方法的有效性和优越性.     

Compensation of droop control using common load condition in DC microgrids to improve voltage regulation and load sharing

DC microgrid is one feasible and effective solution to integrate renewable energy resources, as well as to supply reliable electricity. The control objective of DC microgrids is to obtain system stability, low voltage regulation and equal load sharing in per unit. The droop control is an effectively method adopted to implement the control of microgrids with multiple distributed energy units. However in the application of low-voltage DC microgrids, the nominal reference mismatch and unequal cable resistances require a trade-off to be made between voltage regulation and load sharing. In this paper, a unified compensation framework is proposed using the common load condition in local controller, to compensate the voltage drop and load sharing errors. The voltage deviation is compensated with a P controller while the load sharing is compensated through a PI controller. An additional low bandwidth communication is introduced to share the output current information, and the average output current in per unit is generated to represent the common load condition. The performance of the proposed method is analyzed and compared with basic droop control and hierarchical structure method. The large signal stability is analyzed to define the margin of compensation coefficients. Simulations and experiments are carried out to verify the performance of the proposed method.     

A review of decentralized and distributed control approaches for islanded microgrids: Novel designs,current trends,and emerging challenges

Distributed energy resources (DER) on the demand side have been fast growing, which could boost energy resilience by uninterruptedly supplying the commercial and residential sectors in the form of islanded microgrids when the utility electricity grid is out of service. Nevertheless, simply applying the centralized hierarchical control strategies, traditionally used for utility electricity grids, onto the islanded microgrids would encounter several critical issues. For instance, the control goals in secondary and tertiary control could be activated tardily, the single-point fault could cause critical system failure, and the properties of dynamic plug and play would be hard to achieve. To this end, decentralized and distributed control approaches have been explored to cope with the issues. Specifically, compared to the centralized hierarchical control, decentralized and distributed control strategies can (i) respond to disturbances more promptly, enhancing the performance of islanded microgrids with limited resources; (ii) guarantee system stability especially when a fault occurs and certain DERs are disconnected from the network; and (iii) facilitate deeper penetration of DERs in the microgrid, owning to the low computational complexity and sparse communication network. In this article, the common approaches for decentralized and distributed control are reviewed, and the current design trends and critical technical challenges are discussed to offer a comprehensive understanding of decentralized and distributed controlled microgrids.     

交直流混合微电网接口变换器虚拟同步发电机控制方法

随着分布式发电技术的推广,交直流混合微网以其灵活性正得到越来越广泛的研究和应用,而接口变流器是其核心部件。提出了一种接口变换器虚拟同步发电机控制策略。该策略不仅能使交直流子网有功功率分配更加均匀,还能使系统在大容量负荷投切过程中响应更加平滑,降低交直流子网快速功率波动的耦合影响。Matlab/Simulink仿真算例的验证结果表明,提出的接口变换器虚拟同步发电机控制方法能够降低交直流子网功率传导影响,有利于提高交直流微电网的运行稳定性。