中低压直流变压器拓扑与控制综述

直流变压器作为直流电网中实现电压变换与电能分配的核心装备,其运行特性对直流电网影响深刻.基于此,对中低压直流电网中直流变压器的研究现状进行了总结与分析.首先,简要阐述了直流变压器的基本功能和典型运行场景;考虑到拓扑是直流变压器适应不同电压等级应用场合的关键,从端口数量和能量耦合方式的角度对直流变压器拓扑进行了分类,明确了各类拓扑的主要特征;其次,全面分析了直流变压器在稳态与暂态运行过程中包括效率优化、软启动、直流偏置电流抑制等方面的控制策略,有利于保障直流变压器在复杂工况下的高效可靠运行;然后,对直流变压器核心部件——高频变压器的关键技术进行了讨论,为高频变压器的选型和设计提供了参考;最后,对直流变压器未来的发展趋势进行了展望.     

大规模新能源发电集群直流汇集及输送方案研究

随着多端直流和直流电网等先进输电技术的不断发展,在中国大规模新能源发电基地逐步构建直流汇集与输送系统,并与现有的交流电网互联,形成高比例新能源接入的交直流混联系统,将会成为中国未来电网形态发展的主要特点之一。针对中国西部地区大规模新能源发电集群的直流汇集及输送问题,深入分析了新能源电站场站内部、场站之间的汇集组网方式,并基于分层分区的原则设计了大规模新能源发电集群多层级直流汇集与输送系统方案,在此基础上,以中国甘肃酒泉地区千万千瓦级新能源发电基地为场景,设计了相应的汇集输送方案,并对其输送容量、电压等级、关键设备需求进行了探讨,为未来大规模新能源发电集群的直流汇集与输送方案的研究与建设提供参考。     

大规模海上风电柔性直流输电技术应用现状和展望

海上风电具有风力资源稳定性强、年利用小时数高等特点,随着海上风电机组大型化、投资规模扩大以及建设成本下降,基于柔性直流输电技术的大规模海上风电送出已成为海上风电发展和研究的热点方向。结合国内外典型海上风电柔性直流输电工程,对换流阀、联接变压器、耗能装置、高压直流断路器、海底直流电缆关键电气设备应用现状等进行分析和总结,介绍控制系统构、硬件组成和控制算法研究现状。考虑到海上平台所处的盐雾腐蚀环境,介绍了联接变压器、换流阀的防腐设计和海水冷却系统设计。分析、总结了大规模海上风电的并网技术方案的研究现状,对海上换流站、海上风电场的发展趋势进行展望。     

混合直流输电系统送端交流暂态电压特性研究

对于大规模新能源特高压直流外送系统,受端电网故障可能导致送端电网电压剧烈变化,严重威胁送端电网的安全稳定运行,因此送端电网暂态电压是直流输电系统适应性的重要考虑因素。混合直流输电结合了常规直流和柔性直流的优势。针对大规模新能源混合直流外送应用场景,首先介绍了两端混合直流输电系统典型拓扑,建立了相应数学模型,阐述了基本控制结构。然后分析了当受端交流电网发生短路故障,采用不同直流输电拓扑方案时送端电网的交流暂态电压特性。最后在PSCAD/EMTDC搭建了不同混合直流输电系统仿真模型,验证了上述分析的有效性。     

柔性直流输电技术的工程应用和发展展望

柔性直流输电技术作为新一代的直流输电技术,具有有功无功独立控制、响应快速灵活、扩展性强等突出优点,广泛应用于风电送出、电网互联、无源网络供电和远距离大容量输电等场景。在中国新型电力系统建设的背景下,针对新能源送出和多直流馈入电网安全稳定提升等重大需求,柔性直流输电技术优势将进一步凸显。文中对柔性直流输电技术的发展现状和趋势进行梳理,以多个代表性的柔性直流输电工程为例,系统地阐述了中国柔性直流输电技术的工程实践经验,重点介绍了柔性直流输电技术在新能源送出、电网互联和远距离大容量输电的典型应用及工程运行情况。最后,文中分析了新型电力系统下柔性直流输电技术的发展前景并指出所面临的挑战,为柔性直流输电技术的发展与应用提供参考。     

一种基于电容可控振荡换流的新型直流断路器EI北大核心CSCD

直流输配电网在远距离大容量电能传输、大规模新能源并网和源–网–荷协调控制等领域发挥重要作用。直流断路器(DC circuit breaker,DCCB)作为直流系统实现故障隔离的核心装备,目前还面临开断能力受限、成本高昂等问题,制约其在直流输配电系统中的广泛应用。该文首先提出一种新型电容可控振荡换流原理与拓扑电路,其通过激发电容振荡升压以实现振荡电流的快速提升,从而实现电流的转移与开断;然后对电容振荡换流机理进行数学分析,阐述所提直流断路器(DC circuit breaker,DCCB)拓扑构成与基本原理,并给出核心参数理论设计约束边界。最后,仿真分析20k V/3ms/15k A DCCB技术性能,论证所提拓扑的可行性与技术特点。研究结果表明,所提拓扑损耗低,可快速实现双向短路电流开断,与混合式DCCB相比,所提拓扑全控器件使用数量少、应力小,整体技术经济性能优异,具备良好的应用前景。     

基于高频链直流变压器的柔性中压直流配电系统分析

为了克服柔性中压直流配电网工频方案中变压器体积大、重量大、噪音大、控制不够灵活等问题,提出一种基于高频链直流变压器的柔性中压直流配电系统。该系统中直流配电母线不仅包括中压直流母线,还包括低压直流母线;中低压直流母线之间通过直流变压器进行连接;低压直流母线用于接入各类分布式电源。该系统中高频链直流变压器的使用不仅实现了不同电压等级直流母线间的电压变换、能量管理,还可以有效提高系统功率密度。介绍了中压柔性直流配电系统架构,给出了高频链直流变压器以及其它典型换流器的设计和分析,并对直流配电系统的工作模式和控制器进行了设计。最后,搭建了仿真平台,验证了系统的有效性。     

直流配电网运行控制策略分析及展望

由于直流配电网在新能源消纳、直流负荷接入、网络结构升级等方面具有巨大的优势,近年得到了广泛关注和认可。在减少变流环节、简化控制目标的同时,直流配电网引入了新的不稳定因素,对运行控制提出了新的挑战。首先,总结并分析了直流配电网拓扑结构及特征;然后,对直流配电网典型运行特征及其带来的稳定性问题进行了分析,在此基础上,对直流配电网变流器典型运行控制策略的基本原理、应用场景以及研究方向进行了总结和分析;最后,对直流配电网运行控制的难点和未来研究方向进行了预期和展望。     

新一代低压直流供用电系统关键技术及发展展望

针对当今社会能源变革现状及电力系统发展新趋势,探索了新一代低压直流供用电系统的主要特征、典型应用场景、关键技术及未来研究方向。分析了现代社会的能源变革特点及电力系统的未来发展趋势,指出了发、储、用一体化的新一代低压直流供用电系统的发展需求;分析了新一代低压直流供用电系统的主要特征和典型应用场景,介绍了低压直流供用电系统的电压等级、国际标准及国内外示范工程的进展情况;分析了低压直流供用电系统的关键技术并展望了低压直流供用电系统的发展趋势。最后,对新一代低压直流供用电领域的未来研究方向进行了总结和建议。     

柔性直流输电技术在大电网中的应用与实践

柔性直流输电是基于电压源换流器原理的新型直流输电技术,具有无换相失败、有功无功解耦、运行稳定等优点,改善交直流相互影响问题和提高电网稳定性的作用显著。该文对柔性直流的技术特点和发展现状进行了介绍,系统性地阐述了柔性直流输电技术提升大电网稳定性方面的作用,介绍了我国柔性直流技术在大电网应用的工程实践经验,并展望了新型电力系统下柔性直流技术在电网惯性支撑、大规模新能源传输的新技术,为柔性直流技术在新型电力系统的发展与应用提供参考。     

DC analysis and design of a PWM buck converter operated as a dynamic power supply

Modern energy transmission and signal reproduction techniques rely upon power amplifiers that must operate with high efficiency. An increasingly popular technique for addressing this problem involves replacing the fixed power amplifier supply voltage V _{D D} with a controlled, variable voltage provided by a dynamic power supply. Although pulse‐width modulated dc‐dc buck converters typically function as fixed‐output supplies, this paper provides new theoretical dc analysis for operation wherein the output voltage is controlled and continuously variable over a wide range. A design procedure for the variable‐output buck converter is derived. Key device parameters affecting converter speed and efficiency are identified. The dc analysis and design procedure are verified experimentally, with calculated and measured parameters shown to be in good agreement. Copyright © 2016 John Wiley & Sons, Ltd.     

Integration of a bi-directional DC-DC converter model into a real-time system simulation of a shipboard medium voltage DC system

A bi-directional dc/dc converter model is investigated for a notional Medium Voltage DC (MVDC) shipboard power system to improve energy flexibility and deal with peak energy demand in shipboard power system. Surplus energy in the MVDC system during light load condition can be captured by energy storages distributed in local load zones through the bi-directional dc/dc converters and then can be used during heavy load condition or black starting of the MVDC system. In this paper, the derivation process of the small-signal average models of the isolated-type bi-directional dc/dc converter is presented for controller design. This paper also presents the controller optimization process using intelligent optimal searching algorithm, Particle Swarm Optimization, for optimizing dynamic and steady-state control performance of a bi-directional dc/dc converter. The control performance of the proposed controller is evaluated using frequency-domain analysis and time-domain simulation of the large-scale notional MVDC shipboard power system using the Real-Time Digital Simulator.     

Development of –1 MV DC Filter and High‐Voltage DC Measurement Systems for ITER NBI

This paper presents the development results of a ?1 MV dc filter and dc measurement systems for an ITER (International Thermonuclear Experimental Reactor) neutral beam injector (NBI) system. High accuracy of 0.5% and fast responsivity of 3.3 μs, ?3 dB are required for the dc measurement systems: both dc voltage dividers and DCCTs. Circuit design and thermal flow design were carried out to clarify and minimize their effects on the accuracy and responsivity. The validity of the established design was demonstrated by the actual‐product tests; temperature rise of each components fell below the allowable value; inner components of dc filter withstood dc ?1.2 MV; each voltage divider accurately measured the voltage during the dc ?1.2 MV withstand voltage test; the voltage dividers and the DCCTs were adequate to the requirements of responsivity (3.3 μs, ?3 dB).     

Three-phase,power quality improvement ac/dc converters

The generation of harmonics and reactive power flow in a power system is greatly influenced by the widespread use of power electronic converters in addition to other sources of harmonics and reactive power. The design, development and successful application of single-phase, power quality improvement converters in domestic, commercial and industrial environment has made possible the design and development of three-phase, power quality improvement converters and their widespread use in different applications. This paper deals with a comprehensive review of three-phase, power quality improvement converter configurations, control approaches, performance on supply and load sides in terms of input power factor, THD and well-regulated, reduced-rippled dc output, power rating, cost and selection for specific applications. It also provides state-of-the-art of power quality improvement converter technology to researchers, designers and engineers working on three-phase, switched-mode ac–dc converters.     

DC Fault Clearing Characteristics of a Bulk Power VSC HVDC Transmission System using DC Circuit Breakers

Development of wind power generation resources is considered in Japan. However, long‐distance transmission lines are necessary to utilize the wind power because most of the wind power resources are distant from load centers. A voltage source converter based high voltage dc transmission (VSC HVDC) system is an option to realize their effective use. A VSC HVDC system equipped with dc circuit breakers has been considered to clear the dc line faults promptly. However, the fault clearing characteristics by the dc circuit breakers have not been analyzed very well for the system with the long distance overhead transmission line. This paper focuses on a fault clearing in the VSC HVDC system with long‐distance overhead line by the dc circuit breaker using a new fault detection method. A 2.4‐GW bipolar VSC HVDC system with 600‐km overhead transmission line is modeled and its operation performance is verified by computer simulations. The simulation results demonstrate the detailed fault clearing characteristics with the long transmission line. Moreover, specifications required for the dc circuit breakers are considered in terms of operation delay, peak current, and absorbed energy.     

电动汽车用外转子永磁无刷直流电动机设计

根据电动汽车电动机的特点,提出一种外转子永磁无刷直流电动机,结合一台小功率外转子永磁无刷直流电动机实例,应用电机设计几何相似律,设计了一台电动汽车用外转子永磁无刷直流电动机,并分析了其应用在电动汽车上的可行性.     

飞机高压直流电力系统的发展

20世纪下半叶电工科技的发展使飞机用电设备发生了很大的变化,要求飞机电源和配电系统相应地变化,270V飞机高压直流电力系统在解决了无刷电机电能变换和无触点电器等关键技术后诞生了。F22和F35先后应用270V高压直流电力系统表明该系统已趋成熟并将在21世纪得到更大的发展。     

中压直流配电网中直流变压器工程化应用

文中针对中压直流配电网中直流变压器(DCT)的工程化应用问题,首先归纳实际工程对DCT故障快速恢复、高可靠供电及灵活控制的需求,采用带有隔离半桥的改进型子模块结构,分析其故障阻断、在线冗余、有载调压及均压控制功能。然后,讨论子模块取电方式、整机启动策略及绝缘设计等典型工程问题,比较多种解决方案并进行适应性分析。进一步,重点研究能效提升方法这一工程核心问题,分析硬件及软件上的能效提升措施,并分别从材料选型、高频变压器设计、控制策略改进、系统用能优化等方面提出相应优化策略。最后,探索小型化应用的工程推广前景,从特定场景设计、模块拓扑改进、新型材料应用3个角度分别提出一种小型化方案,阐明现有技术瓶颈并提出相应解决思路。     

A new topology for nonisolated multiport zero voltage switching dc‐dc converter

In this paper, a new multiport zero voltage switching dc‐dc converter is proposed. Multiport dc‐dc converters are widely applicable in hybrid energy generating systems to provide substantial power to sensitive loads. The proposed topology can operate in 3 operational modes of boost, buck, and buck‐boost. Moreover, it has zero voltage switching operation for all switches and has the ability to eliminate the input current ripple; also, at low voltage side, the input sources can be extended. In addition, it has the ability of interfacing 3 different voltages only by using 3 switches. In this paper, the proposed topology is analyzed theoretically for all operating modes; besides, the voltage and current equations of all components are calculated. Furthermore, the required soft switching and zero input currents ripple conditions are analyzed. Finally, to demonstrate the accurate performance of the proposed converter, the Power System Computer Aided Design(PSCAD)/Electro Magnetic Transient Design and Control(EMTDC) simulation and experimental results are extracted and presented.