下载文档原格式
MMC-HVDC系统环流控制策略研究MMC（Modular Multilevel Converter）-HVDC（High Voltage Direct Current）系统是一种新型的高压直流输电系统，具有较高的调节能力和稳定性。
然而，在实际运行中，MMC-HVDC系统中存在环路电流问题，可能导致系统发生振荡和不稳定。
因此，研究MMC-HVDC系统环流控制策略成为了当前研究的热点之一。
MMC-HVDC系统中的环流问题主要是由于逆变器之间的电容不完全匹配所引起的。
MMC-HVDC系统采用了分阶段放电和光纤通信等控制手段，可以有效地降低电容不匹配带来的环流问题。
然而，由于环流问题会对系统有害影响，因此需要寻找一种有效的控制策略来解决。
在MMC-HVDC系统中，环流控制策略主要分为有源环流控制和无源环流控制两种方式。
有源环流控制是通过调整逆变器中的导纳来抑制环流的产生，常用的方法有阻抗调节和自适应控制。
无源环流控制则是通过改进电容模块的电路结构和控制算法来减小环流的幅值和频率，常用的方法有改进电容模块的结构和采用非接触式的电容传感器等。
具体到MMC-HVDC系统中的环流控制策略研究，一种常用的方法是采用模型预测控制（MPC）策略。
MPC是一种基于模型的先进控制策略，具有快速响应、稳定性好等优点。
在MMC-HVDC系统中，利用MPC策略可以对逆变器的调制信号进行优化设计，从而实现环流的控制。
另外，还可以采用基于频率的环流控制策略，通过控制逆变器的工作频率和相位来抑制环流的产生。
在MMC-HVDC系统环流控制策略研究中，需要充分考虑系统的安全稳定性和经济性。
首先，要根据实际运行情况和系统参数对控制策略进行合理选择，以保证系统的安全稳定运行。
其次，要在保证系统安全性的前提下，尽可能减少环流控制的成本和能耗，提高系统的经济性。
最后，还应对不同的故障情况进行仿真和分析，评估环流控制策略在不同工况下的效果。
综上所述，MMC-HVDC系统环流控制策略研究是当前研究的一个重要方向。
第50卷第1期电力系统保护与控制Vol.50 No.1 2022年1月1日Power System Protection and Control Jan. 1, 2022 DOI: 10.19783/ki.pspc.201639新型模块化多电平换流器的设计与应用于 飞，王子豪，刘喜梅(青岛科技大学自动化与电子工程学院，山东 青岛 266061)摘要：随着电力系统电压等级的不断升高，模块化多电平换流器(Modular Multilevel Converter, MMC)桥臂中串联的子模块数量增多，硬件成本升高，制约了其在直流输电系统中的发展。
针对这些问题，通过分析多电平换流器和现有的阶调式模块化多电平变换器(Gradationally Controlled Modular Multilevel Converter, GC-MMC)的工作原理，提出了一种新型的换流器。
为了解决新型逆变器的电容电压平衡问题，提出了一种适用于新型逆变器的新型稳压算法。
最后在Matlab/Simulink环境下搭建了双端标幺值控制的柔性直流输电系统，将新型逆变器应用于系统中进行了验证。
仿真结果表明，新型换流器输出电平数量比普通MMC多，输出交流侧和直流侧的波形质量达到直流输电要求。
通过对新型逆变器和普通MMC分别进行成本计算，结果表明新型逆变器的建设成本大大少于普通MMC。
关键词：模块化多电平换流器；阶调式多电平逆变器；阶调式模块化多电平变换器；电容电压平衡算法A gradationally controlled modular multilevel converter and its applicationYU Fei, W ANG Zihao, LIU Ximei(College of Automation & Electric Engineering, Qingdao University of Science & Technology, Qingdao 266061, China)Abstract: With the increasing voltage level of power systems, the number of serial sub-modules in the bridge arm of a modular multilevel converter (MMC) increases, and the hardware costs increase. This restricts its development in the direct current transmission system. In order to solve these problems, a new type of converter is proposed by analyzing the working principle of a multi-level converter and the existing gradationally controlled modular multilevel converter (GC-MMC). In order to solve the problem of capacitor voltage balance of the new inverter, a new voltage regulation algorithm suitable for the new inverter is proposed. Finally, in the Matlab/Simulink environment, a flexible HVDC transmission system based on the new inverter's double-terminal SCM unit value control is built and verified. The simulation results show that the output level of the new converter is more than that of the common MMC, and the quality of the waveform of the output AC and DC side can meet the requirements of DC transmission. Through the cost calculation of the new inverter and the common MMC respectively, the results show that the construction cost of the new inverter is much less than the common MMC.This work is supported by the National Natural Science Foundation of China (No. 61803219).Key words: MMC; gradationally controlled multi-level inverter; GC-MMC; capacitor voltage balancing controlled algorithm0 引言随着电力系统的不断发展，电力系统的规模也在不断扩大，直流输电[1-3]已经成为我国电力输电的重要组成部分。
柔性直流输电技术介绍1引言柔性直流输电技术（Voltage Sourced Converter,VSC）是一种以电压源变流器、可关断器件（如门极可关断晶闸管（GTO）、绝缘栅双极晶体管（IGBT））和脉宽调制（PWM）技术为基础的新型直流输电技术。
国外学术界将此项输电技术称为VSC-HVDC，国内学术界将此项输电技术称为柔性直流输电，制造厂商ABB 公司与西门子公司分别将该项输电技术命名为HVDC Light和HVDC Plus。
与传统基于晶闸管的电流源型直流输电技术相比，柔性直流输电技术具有可控性高、设计施工方便环保、占地小及换流站间无需通信等优点，在可再生能源并网、分布式发电并网、孤岛供电、城市电网供电等方面具有明显的优势。
随着大功率全控型电力电子器件的迅速发展，柔性直流输电技术在高压直流输电领域受到越来越广泛的关注及应用。
传统的低电平VSC具有开关频率高、输出电压谐波大、电压等级低、需要无源滤波器等缺点，而且存在串联器件的动态均压问题；多电平变流器提供了一种新的VSC实现方案。
它通过电平叠加输出高电压，逼近理想正弦波，输出电压谐波含量少，无需滤波设备。
自1997年赫尔斯扬试验工程投入运行以来，柔性直流输电技术迅速发展，目前已有13项工程投入商业运行，最高电压等级已达±200kV，最大工程容量达到400MW，最长输电距离为970km。
通过各个领域专家的不断创新和工程建设运行经验的不断积累，柔性直流输电技术作为一种先进的输电技术已具备大规模应用的条件。
图1两端VSC-HVDC系统典型结构图2008年12月，“柔性直流输电关键技术研究与示范工程”作为国家电网公司的重大科技专项正式启动。
该工程联接上海南汇风电场与书院变电站，用于上海南汇风电网并网，是中国首条柔性直流输电示范工程。
该工程由中国电力科学研究院开发，负责接入系统设计、设备供货及工程实施等工作。
2柔性直流输电技术的研究现状2.1高压大容量电压源变流器技术2.2.1模块化多电平变流器（Modular Multilevel Converter,MMC）模块化多电平变流器可以有效降低交流电压变化率，其拓扑结构如图2所示。
多端柔性直流输电(VSC—HVD)系统直流电压下垂控制学院：姓名：学号：组员：指导老师：日期：摘要：多端柔性直流输电系统(voltage sourcedconverter basedmulti-terminal high voltage direct current transmission，VSC-MTDC)与传统的电网换相换流器构成的多端直流输电系统相比，具有控制灵活、能够与短路容量较小的弱交流系统甚至无源交流系统相连、扩建容易等诸多优点直流电压的稳定直接影响到直流潮流的稳定，因此直流电压控制是多端柔性直流输电系统稳定运行的重要因素之一。
下垂控制策略具有无需通讯、可靠性较高等优点，但存在直流电压质量较差、功率分配不独立、参数设计困难等问题。
本文首先介绍了多端柔性直流输电系统控制方法的分类比较，然后重点介绍了下垂控制数学模型，分析MTDC 系统中下垂控制参数对直流电压与电流(功率)的影响机理，研究满足MTDC 系统功率平衡和直流电压稳定的V-I(V-P)下垂特性曲线。
关键词：VSC-MTDC 下垂控制模块化多电平换流器一、引言基于电压源换流器（Voltage Source Converter，VSC）的高压直流输电（High Voltage Direct Current，HVDC）技术（HVDC based on VSC，VSC-HVDC，也称柔性直流输电技术）系统以其灵活性、经济性和可靠性，在新能源并网、城市直流配电网、孤岛供电等领域有着广泛的应用前景。
MTDC 系统接线方式分为串联、并联和混联等，目前主要采用并联式[1]。
并联接线的MTDC 系统中所有VSC 工作于相同直流母线电压下，因此直流电压控制是系统稳定运行的关键，类似于交流系统中的频率控制。
多端柔性直流输电系统级直流电压控制策略可以分为三大类，分别是单点直流电压控制策略、多点直流电压控制策略以及直流电压斜率控制策略。
单点直流电压控制策略将一个换流站作为直流电压控制站，其余换流站负责控制其他的变量，例如交流功率、交流频率、交流电压等，系统中仅有一个换流站对直流电压进行控制，如果这个换流站失去了直流电压的控制能力，整个柔性直流输电系统的潮流将失稳，因此单点直流电压控制策略的适用性较差。
MMC型柔性直流输电系统建模、安全稳定分析与故障穿越策略研究1. 本文概述随着全球能源需求的不断增长和电网规模的扩大，柔性直流输电技术（MMCHVDC）因其高效率、高可控性和良好的故障穿越能力而成为现代电网的重要组成部分。
本文旨在深入探讨MMC型柔性直流输电系统的建模方法、安全稳定特性分析以及故障穿越策略，以期为实际工程应用提供理论支持和策略指导。
本文将详细阐述MMCHVDC系统的基本原理和结构特点，为后续建模和分析奠定基础。
本文将重点探讨MMCHVDC系统的数学建模方法，包括其交流侧和直流侧的动态模型，以及控制器的设计。
这部分内容将采用现代控制理论，结合仿真软件进行模型验证，确保模型的准确性和实用性。
在安全稳定分析部分，本文将基于所建立的模型，分析MMCHVDC 系统在各种运行条件下的稳定性，包括正常运行、负载变化和故障情况。
特别地，本文将重点研究系统在直流侧和交流侧故障时的响应特性，以及这些故障对系统稳定性的影响。
本文将提出一套完整的故障穿越策略，以增强MMCHVDC系统在电网故障时的鲁棒性和稳定性。
这些策略将涵盖故障检测、故障隔离、系统恢复等多个方面，旨在确保系统能够在各种故障情况下保持稳定运行，最大限度地减少故障对电网的影响。
总体而言，本文的研究成果将为MMC型柔性直流输电系统的设计、运行和控制提供重要的理论参考和实践指导，有助于推动该技术在智能电网和可再生能源领域的广泛应用。
2. 型柔性直流输电系统概述MMC（Modular Multilevel Converter）型柔性直流输电系统，作为一种新型的电力电子输电技术，以其独特的模块化设计和优越的电力调节能力，近年来在高压直流输电（HVDC）领域受到了广泛关注。
该系统主要由多个子模块组成，每个子模块包含一个绝缘栅双极晶体管（IGBT）和反并二极管，以及相应的电容器。
通过控制IGBT的开关状态，可以实现对电压的精确控制，从而实现有功和无功的独立控制。
模块化多电平换流器的均压优化控制仿真研究摘要本文主要对模块化多电平换流器(modular multilevel converter, MMC) 中的均压优化控制进行的研究，整个模块化多电平换流器仿真需要将输入的三相交流电转化为直流电，并且各个子模块电压差值需要尽量的小，从而保证整个系统能够稳定运行，对载波移相脉宽调制策略进行推导与改进，使得模块化多电平换流器能够在更短的时间内稳定，且子模块电容电压在合理的控制中保持均衡。
仿真实验结果证明了所提方法的正确性和可行性。
关键词模块化多电平换流器；子模块均压；载波移相脉宽调制Simulation Study on Optimal Voltage Equalization Control ofModular Multi-level ConverterZ5号宋体oufucheng Daipanyang(Aba Teachers University,Si chuan Wenchuan,China )Abstract This paper mainly studies the voltage optimizationcontrol in Modular Multilevel Converter. The whole modular multi-level converter simulation needs to convert the input three-phase AC into DC, and the voltage difference between each sub-module needs to be assmall as possible. Thus, the whole system can run stably, and the strategy of carrier phase-shifted PWM is deduced and improved, so that the modular multi-level converter can be stable in a shorter time, andthe capacitance voltage of the sub-modules can be balanced in a reasonable control.The simulation experiment results prove the correctness and feasibility of the proposed method.keywords MMC; sub-module voltage equalizer; carrier phase shift PWM引言随着西电东送工程的实施，电能的损耗也随着高压长距离输电不断增大，从而使得直流输电在电力传输中脱颖而出。
具有直流故障阻断能力的MMC-HVDC系统拓扑研究具有直流故障阻断能力的MMC-HVDC系统拓扑研究摘要：高压直流输电（HVDC）作为一种重要的电力传输技术，已经广泛应用于大规模电力输送。
然而，在HVDC系统中，直流故障带来的挑战一直是一个重要问题。
为了解决这个问题，多级换流器Modular Multilevel Converter（MMC）的HVDC系统被设计和研究，以具备直流故障阻断能力。
本文对具有直流故障阻断能力的MMC-HVDC系统的拓扑结构进行了研究，并分析了其工作原理和特点。
研究结果表明，具有直流故障阻断能力的MMC-HVDC系统在处理直流故障时表现出较高的稳定性和可靠性，有望在HVDC系统中得到广泛应用。
关键词：高压直流输电；Modular Multilevel Converter；直流故障阻断能力；拓扑结构引言高压直流输电（HVDC）作为一种重要的电力传输技术，已经广泛应用于远距离、大容量、跨境等特殊条件下的电力输送[1]。
然而，在HVDC系统中，直流故障问题成为限制其应用的一个重要问题。
直流故障的发生会对电力系统的稳定性和可靠性产生严重影响，而传统的HVDC系统往往无法有效应对这些直流故障。
因此，如何使HVDC系统具备直流故障阻断能力成为了一个研究的热点和难点。
为了解决HVDC系统中直流故障问题，研究人员提出了多种方案，其中一种重要的方案是采用多级换流器Modular Multilevel Converter（MMC）技术[2]。
MMC是一种基于半导体器件的多电平换流器，具备较高的可控性和可靠性。
相比传统的两级换流器，MMC系统能够实现较高的电压平衡、较低的谐波波动和较小的电流冲击。
此外，MMC系统还具备直流故障阻断能力，能够在直流故障发生时保证系统的稳定运行。
MMC-HVDC系统是一种具有直流故障阻断能力的HVDC系统，其拓扑结构主要包括两级MMC子模块和直流侧接口电感[3]。
MMC-HVDC系统数学模型及其控制策略曹春刚;赵成勇;陈晓芳【摘要】Modular multilevel converter (MMC) is a new topology in VSC-HVDC,which is different from the conventional two level VSC. Therefore.it is significant to study the modeling and control strategy of MMC-HVDC. The topology and working principle of MMC are introduced in this paper. Considering the reactance of the bridge, the mathematic model of the MMC-HVDC was developed, and the simplified circuit diagram of MMC-HVDC was obtained. The 21-level MMC-HVDC system was constructed in PSCAD/EMTDC environment. In the synchronous dq reference frame, the feed forward compensation control strategy is applied, and the simulation results verify that the mathematical model is correct and the control strategy is effective.%模块化多电平换流器MMC(modular multilevel converter)是电压源换流器型直流输电领域的一种新型拓扑,与传统的两电平存在一定的不同,因而对其建模及控制策略进行研究,有重要的意义.论文介绍了MMC的拓扑结构及工作原理.在考虑桥臂电抗的基础上,推导出模块化多电平换流器型直流输电MMC-HVDC(modular multilevel converter-high voltage direct current)的数学模型,进一步得到MMC-HVDC的简化电路图.在PSCAD/EMTDC下搭建了21电平MMC-HVDC系统,在dq同步旋转坐标系下,采用前馈解耦控制策略进行仿真研究,仿真结果验证了该数学模型的正确性和控制策略的有效性.【期刊名称】《电力系统及其自动化学报》【年(卷),期】2012(024)004【总页数】6页(P13-18)【关键词】模块化多电平换流器;桥臂电抗;数学模型;简化电路图;控制策略【作者】曹春刚;赵成勇;陈晓芳【作者单位】华北电力大学(保定)电气与电子工程学院,保定071003;华北电力大学(保定)电气与电子工程学院,保定071003;华北电力大学(保定)电气与电子工程学院,保定071003【正文语种】中文【中图分类】TM721.1电压源换流器型直流输电VSC-HVDC(voltage source converter-high voltage direct current)，具有有功无功灵活可调、占地面积小、环境污染小、具备黑启动能力等显著优点，在可再生清洁能源(如风能和太阳能)的大力开发和利用，城市配电网转入地下改造等领域得到越来越广泛的应用[1～5]。
基于MPC的MMC-HVDC子模块均压控制策略张明光;李波【摘要】模块化多电平换流器(Modular Multilevel Converter,MMC)具有效率高、谐波小、模块化设计和易级联等优点,在高压大容量电能变换领域得到了广泛应用.为提高基于模块化多电平换流器的直流输电系统(MMC-HVDC)运行的动态响应速度,提出了一种基于模型预测控制(Model Predictive Control,MPC)与改进的子模块均压控制策略相结合的方法,通过预测模型、反馈校正和滚动优化得到最优的电压控制量,克服了传统的内环电流控制器与外环控制器中PI参数整定困难和动态响应慢的问题.最后,在PSCAD-EMTDC软件平台搭建了21电平的MMC-HVDC系统仿真模型.仿真结果验证了控制策略的有效性和可行性.【期刊名称】《电气自动化》【年(卷),期】2018(040)005【总页数】4页(P66-69)【关键词】模型预测;MMC-HVDC;开关频率;子模块均压;滚动优化;排序算法【作者】张明光;李波【作者单位】兰州理工大学电气工程与信息工程学院,甘肃兰州 730050;甘肃省工业过程先进控制重点实验室,甘肃兰州 730050;兰州理工大学电气与控制工程国家级实验教学示范中心,甘肃兰州 730050;兰州理工大学电气工程与信息工程学院,甘肃兰州 730050;甘肃省工业过程先进控制重点实验室,甘肃兰州 730050;兰州理工大学电气与控制工程国家级实验教学示范中心,甘肃兰州 730050【正文语种】中文【中图分类】TM460 引言模块化多电平换流器(Modular Multilevel Converter，MMC)作为一种新型的电压源型换流器结构[1]，采用子模块SM(Sub-Module)级联型拓扑，其模块化结构易于扩展，可通过增加或减少串联子模块的数量，灵活地改变应用的电压等级[2]。
与传统两电平或三电平电压源换流器(Voltage Source Converter，VSC)相比，MMC开关频率较低，输出电流的谐波含量少，对电力电子开关的一致性要求较低[3-4]，在高压直流输电领域具有广阔的应用前景[5]。
专利名称：MODULAR MULTILEVEL DC/DC CONVERTER FOR HVDC NETWORKS发明人：LEHN, Peter Waldemar,KISH, GregoryJoseph申请号：CA2014/050380申请日：20140416公开号：WO2014/169388A1公开日：20141023专利内容由知识产权出版社提供专利附图：摘要：The apparatus comprises one or more strings, each string: comprising two pairs of arms, each pair of arms being defined by an inner arm and an outer arm, series-stackedaround an associated node, each arm being defined by a plurality of cascaded submodules; and in use, being connected to one of the networks such that the arms are arranged in symmetric relation about an associated midpoint, with the inner arms flanked by the outer arms. The nodes, in use, are coupled to the other of the networks, for transfer of DC power between the networks. Means for providing paths for circulating AC currents are provided along with means to achieve power balance of submodules notwithstanding the DC power transfer.申请人：THE GOVERNING COUNCIL OF THE UNIVERSITY OF TORONTO地址：CA国籍：CA代理人：RIDOUT & MAYBEE LLP et al.更多信息请下载全文后查看。
MMC-HVDC直流侧故障分析及故障限流方法研究摘要：MMC-HVDC（Modular Multilevel Converter-HVDC）直流侧的故障分析和故障限流方法研究是HVDC技术领域中一个具有挑战性的研究问题。
本文通过分析MMC-HVDC直流侧出现的常见故障类型、故障机理和故障影响，提出了一种基于MMC-HVDC直流侧能量存储的故障限流方法，并对该方法的效果进行了数值仿真验证。
研究表明，该方法能够有效地限制MMC-HVDC直流侧的故障电流，保证整个系统的稳定性和安全性。
关键词：MMC-HVDC，故障分析，故障限流，能量存储，数值仿真1. 引言MMC-HVDC技术作为现代输电技术的代表，已经得到了广泛的应用。
MMC-HVDC直流侧的故障分析和故障限流方法研究是HVDC技术领域中一个具有挑战性的研究问题。
直流侧故障的出现不仅会导致电力系统的不稳定，还可能对设备损坏和人身安全造成威胁。
因此，对于MMC-HVDC直流侧的故障分析和故障限流方法研究具有重要的理论和应用意义。
2. MMC-HVDC直流侧故障类型及机理MMC-HVDC直流侧存在的故障类型主要包括母线短路、电容器故障和IGBT开关故障等。
针对这些故障类型及其机理，本文分别详细阐述，并通过仿真模拟分析其对MMC-HVDC直流侧电路的影响。
3. 基于MMC-HVDC直流侧能量存储的故障限流方法MMC-HVDC直流侧的故障限流方法是实现直流侧故障保护的重要手段。
本文提出了一种基于MMC-HVDC直流侧能量存储的故障限流方法，并给出了具体的实现步骤。
同时，采用Matlab/Simulink仿真工具对该方法进行了数值仿真验证。
4. 数值仿真结果分析通过对MMC-HVDC直流侧故障限流方法的数值仿真，本文得出了在不同故障情况下的电流波形图、电压波形图和功率波形图，并通过对仿真数据进行分析，验证了该方法的有效性和优越性。
5. 结论本文研究了MMC-HVDC直流侧故障分析及故障限流方法，并提出了一种基于MMC-HVDC直流侧能量存储的故障限流方法。
mmc拓扑特点-回复MMC（Modular Multilevel Converter）是一种新型的多电平变流器拓扑结构，具有许多独特的特点和优势。
在本文中，我们将逐步回答MMC 拓扑特点相关的问题，以帮助读者深入了解MMC的特性和应用。
第一部分：MMC拓扑结构的基本原理和组成MMC的基本原理是利用多个单元级联，通过各级单元的调制和控制实现电力的转换和控制。
MMC由多个H桥单元组成，每个单元都有一个正对称和一个负对称的半桥，通过串联连接形成多个级联的单元。
1. 什么是MMC拓扑结构？MMC是一种多电平变流器拓扑结构，由多个单元级联组成，能够实现高电压和高功率的变换和控制。
2. MMC的基本组成是什么？MMC由多个H桥单元组成，每个单元由两个逆并联的IGBT器件和二极管组成。
每个单元还包括一个电容和一个电感。
第二部分：MMC拓扑结构的特点和优势MMC拓扑结构具有许多特点和优势，下面我们将逐一介绍。
3. MMC拓扑结构具有什么样的电压水平？MMC拓扑结构可以实现多个电平的输出电压，从而减小谐波成分，提高输出电压质量，并且可以提供可调节的输出电压。
4. MMC拓扑结构的功率损耗小吗？由于MMC采用模块化结构，每个单元的功率损耗都比较小，整个系统的总功率损耗相对较低。
5. MMC拓扑结构的可靠性如何？MMC由多个单元级联组成，每个单元都可以独立控制，所以即使其中一个单元出现故障，整个系统仍然可以正常工作，具有较高的可靠性。
6. MMC拓扑结构的响应速度怎样？MMC的每个单元都有独立的控制系统，可以实现快速响应，并且由于模块化结构，可以同时进行多个操作。
7. MMC拓扑结构的容量扩展性如何？由于MMC是模块化的结构，可以根据需要添加或移除单元，从而实现容量的扩展或收缩。
第三部分：MMC拓扑结构的应用领域MMC拓扑结构由于具有多种特点和优势，在许多领域得到了广泛应用。
8. MMC在电力系统中的应用有哪些？MMC可以用于高压直流输电（HVDC）系统、柔流输电（FACTS）系统以及电能质量调节等方面，能够提高电力系统的稳定性和可靠性。
电力电子变压器原理现状应用场合介绍电力电子变压器（Power Electronics Transformer，PET）是一种结合了电力电子技术与变压器的新型电力转换装置。
它通过使用电力电子器件，能够实现高效率的电力转换，并具有可调性和可控性的特点，可以适用于多种电力系统应用场合。
电力电子变压器的原理是基于通过电力电子器件实现的电力转换原理。
它主要由直流侧和交流侧组成。
在直流侧，电力电子变压器通过电力电子器件（如IGBT、MOSFET等）实现可控的直流电压源。
在交流侧，电力电子变压器通过PWM（Pulse Width Modulation）调制技术，控制电力电子器件的开关周期和占空比，实现对输出交流电压波形和频率的调节。
通过这种方式，电力电子变压器能够实现对电压进行变换、调节和控制。
电力电子变压器的现状可以分为实验室研究和实际应用两个方面。
在实验室研究方面，科研人员进行了大量的理论分析和仿真研究，并取得了一定的成果。
目前已经研究出多种不同的拓扑结构和控制策略，如MMC （Modular Multilevel Converter）、HVDC（High Voltage Direct Current）、MC（Matrix Converter）等。
这些研究成果为电力电子变压器的实际应用提供了理论基础和实验验证。
在实际应用方面，电力电子变压器已经在一些特定的场合得到了应用。
例如，它可以用于电力系统中的电压和频率调整、电力质量改善等方面。
此外，电力电子变压器还可以用于电动汽车充电站、可再生能源发电系统等领域。
由于电力电子变压器具有高效能、小体积、可调性强等特点，它能够提高电能利用率，减小设备体积，提高工作效率，并且能够适应不同应用场合的电力转换需求。
电力电子变压器的应用场合可以分为传统电力系统和新能源系统两个方面。
在传统电力系统方面，电力电子变压器可以用于变频调速、无功补偿、过电压保护等方面。
例如，它可以用于电力系统中的HVDC输电、FACTS（Flexible Alternating Current Transmission System）等方面。
深远海风并网三种输电技术比较利用远海风能是海上风电未来发展的重要趋势，德国、英国等海上风电大国都已布局深远海域风电项目。
欧洲、美国及日本远海风电可开发资源储量丰富，并且占海上总可开发资源的比例均超过60%。
从风资源分布上来看，根据国家气候中心研究结果显示，我国海域5~50米水深、70米高度海上风能储量约5亿千瓦，而50米水深以上的深水区域风能储量约为13亿千瓦，占比超过60%，远高于浅水区域。
（按照国际通用惯例以及实际工程经验，一般认为水深大于50米为深海风电，场区中心离岸距离大于70千米为远海风电）。
全球远海风电储量与近海风电场相比，深远海风电场的送出通道与并网方式面临更严苛的要求。
大容量海上风电远距离送出是深远海风电开发利用的关键环节。
目前主要有三种输电技术可以实现海上风电并网：高压交流（high voltage alternating current, HVAC）送出、高压直流（high voltage direct current, HVDC）送出以及分频输电（fractional frequency transmission system,FFTS）送出技术。
HVAC的海上风电送出基于高压交流输电技术（HVAC）的海上风电送出方案仍然是目前并网的主要方式。
海上风机输出工频电能经海上升压站汇集升压后，由工频交流电缆送出并最终接入陆地电网。
海上风电HVAC并网方式工频高压交流送出方式结构相对简单、技术成熟、工程经验丰富，但由于电缆充电电流和充电功率的限制，传输距离有限，且电压等级越高，充电电流越大，一般只适用于离岸小于70 km、容量小于400MW的近海风电场送出。
在电缆两端进行无功补偿是延长电缆输送距离的有效手段之一，但技术上由于电缆载流量的约束，无功补偿容量有限。
若想进一步延长输送距离，需要换用截面积更大的电缆或在海上增设无功补偿站进行中端补偿。
目前世界上采用HVAC并网且离岸最远的海上风电场是位于英国北海地区的Hornsea ProjectOne。
基于改进控制策略的MMC-HVDC运行特性研究孙黎;胡峰;穆钢【摘要】Modular Multilevel Converter (MMC), as a new type of topology, has attracted much attention in the research on HVDC system. However, there are some problems such as low anti-jamming capability and unstable output in their internal control systems. According to these problems, this paper improves the systemic control on the basis of original control strategy. The improved control strategy not only can realize independent control of active power and reactive power as well as stable control of the DC voltage, but also can reduce the oscillation amplitude and cut downthe recovery time, as a consequence the transient and steady-state performance are improved efficaciously. This paper establishes MMC-HVDC two AC systems and conducts the contrastive simulation analyses between the improved control strategies and original strategies in the Matlab/Simulink. The results verify the correctness and validity of the theory.%模块化多电平换流器(MMC)作为一种新型拓扑结构,在高压直流输电系统研究中备受瞩目.但其内部控制系统中,存在抗干扰能力低,输出不稳定等问题.根据上述问题,在原有控制策略的基础上,对系统级控制进行改进.该系统不仅能够实现有功、无功独立控制和直流电压稳定控制,且减小了扰动振荡幅度和故障后恢复时间,有效地改善了系统暂稳态特性.在Matlab/Simulink环境下,搭建改进的MMC-HVDC两端有源系统,对改进前后的控制策略进行对比仿真分析.结果验证了理论的正确性与有效性.【期刊名称】《电力系统保护与控制》【年(卷),期】2018(046)009【总页数】7页(P10-16)【关键词】直流;模块化多电平换流器;控制策略;仿真;运行特性【作者】孙黎;胡峰;穆钢【作者单位】华北电力大学电气与电子工程学院,北京 102206;东北电力大学电气工程学院,吉林吉林 132012;东北电力大学电气工程学院,吉林吉林 132012【正文语种】中文随着高压直流输电技术的飞速发展，基于全控型电压源换流器的高压直流输电系统(Voltage Source Converter based High Voltage Direct Current, VSC-HVDC)因其独立控制有功无功、能量双向传输、适应于各类输电场合，且不存在换相失败等诸多优势，被广泛应用于大城市负荷中心、海上钻井平台、海岛供电和新能源等直流输电工程[1-4]。
Modular Multilevel Converters and HVDC/FACTS: a success storyDr. Hans-Joachim KnaakSIEMENS AGGuenther-Scharowsky-Str. 2D-91058 Erlangen, GermanyTel.: +49 / (9131) – 7.22523Fax: +49 / (9131) – 7.33199E-Mail: Hans-Joachim.Knaak@URL: /energy/hvdcKeywordsHVDC, FACTS, Multilevel converters, Voltage Source Converter (VSC), Power transmissionAbstractThe first modular multilevel converter for HVDC application went operational in 2010. The Trans Bay Cable project transfers 400 MW of electrical power from Pittsburg, CA to the city of San Francisco, via a subsea cable of 88 km. It clearly demonstrated that the advantages of this technology are not only of theoretical nature, but can also be achieved in practice: efficiency comparable to thyristor-based HVDC plants, very low space consumption due to the absence of filters and, most important for the customer, a very good reliability. In the meantime, Siemens was awarded several HVDC PLUS®contracts reaching transmission capacities of up to 1000 MW. The same success could be achieved for Static VAR Compensators (SVC) based on the modular multilevel concept. Both products will certainly play a vital role in meeting the future challenges imposed upon the transmission grids, like integration of large amounts of renewable energy sources or increasing the power transmission capability of the existing grids.IntroductionSince the early days of HVDC transmission, engineers have liked the idea of a self-commutated inverter. However, only the line-commutated, thyristor-based inverter was able to deliver the demanded high power ratings. With the IGBT developing in the high voltage and high current area, voltage source converters for HVDC and FACTS became feasible. Series connection of IGBT press pack components and PWM principle opened new application areas, but did not really spread out, maybe due to the higher losses compared to LCC technology.With HVDC PLUS® and SVC PLUS® Siemens introduced the modular multilevel converter (MMC) technology for power transmission purposes. These article reports on the experience gained with the Trans Bay Cable project, supplying a power of 400 MW to the city of San Francisco, and with the first SVC PLUS® projects. Also, the new projects being rewarded to Siemens are presented, concluding with an outlook on the future challenges in the HVDC and FACTS market.The modular multilevel technologySelf-commutated converters have well-known advantages compared to line-commutated converters (LCC). Active and reactive power can be adjusted independently, they produce fewer harmonics and they offer a black-start capability. When they were first introduced to high voltage applications, the well-proven scheme of the drives world was used: two- or three-level VSC with PWM control. It was adapted to the necessary high voltages by series connection of special IGBT components, being able to carry the current even after a component failure. These converters work well, but some drawbacks were calling for new ideas.Fig. 1: Voltage output of two-level converter (left) and modular multi level converter (right)The output voltage of a two-level converter must be filtered to eliminate the pulse frequency and the high voltage gradients. The filter needs space, generates losses and, a factor which turns out to beincreasingly important, could impose some restrictions in terms of dynamic stability. In order to keep the filter as small as possible, the pulse frequency should be as high as possible. Especially with high voltage power electronic components, the high pulse frequency always comes with high losses. With two- or three-level converters, quite a good compromise can be found, but with modular multilevel converters no filter is needed and the resulting switching frequency is considerably lower.The basic idea of the MMC is to create a variable voltage source in every converter arm, allowingindependent control of the three AC voltages and the DC voltage. This in turn offers something really important for energy transmission: the converter can act on any unsymmetrical or distorted voltage, on AC or DC side, showing passive behaviour or actively improving the voltage or current waveforms.Fig. 2: MMC principle I: controlled voltage sourcesIn the MMC, the adjustable voltage sources are put into practice by a series connection of a number of converter submodules, which can individually be switched on and off, see Fig. 3. Given that thesubmodule capacitor is charged to its nominal voltage, the IGBT switches can apply this voltage to the terminals (“on”), or they can directly connect the terminals (“off”). In case of a full bridge submodule, Realized voltage close to sine wave,even with a low number of submodulesthe capacitor voltage can additionally be connected with negative polarity. The mechanical switchshown in the submodule sketch gives the opportunity to connect the terminals in case of a malfunction of the components inside the submodule, raising the availability to the high level needed in energy transmission. With this protective equipment, standard IGBT modules can be used.With a capacitor voltage in the range of some kV and a DC voltage in the range of some hundreds of kV the output voltage is extremely close to the sinusoidal waveform wanted. Moreover, the converter is able to react instantaneously to any demand, without being slowed down by energy stored in filters or a DC capacitor at the output. The “only” prerequisite is the use of an appropriate control algorithm, taking care of the voltage of each of the capacitors in a converter arm and balancing the six converter arms at the same time. This task is quite demanding, but the feasibility was successfully demonstrated during the first HVDC PLUS ® project.Projects deliveredIn 2007, Siemens was awarded the Trans Bay Cable project, feeding electrical energy directly into the heart of San Francisco. The sending station is located near Pittsburg, CA, the cable is buried in the seabed of the San Francisco Bay. DC transmission was necessary because of the length of the submarine cable. With 88 km of length it clearly exceeds the limit for AC transmission, which is about 70 km. The decision for HVDC PLUS® was mainly driven by the low space requirements for the substations.With more than 200 submodules per converter arm, the MMC delivers up to 400 MW at a voltage of ±200 kV. The control is connected to every submodule by a pair of fibre optics. During the commissioning phase the function could be successfully demonstrated. As usual, this included power reversals, operation during transients and of course the proper functioning of all protection features. Since then, the operation not only proved the feasibility, but also the ability of the MMC scheme to cope with the high demands for power transmission availability.Fig. 4: Valve hall of the Trans Bay Cable project, San FranciscoBeing not as spectacular as HVDC projects, the FACTS projects should not be under-estimated. They certainly help stabilizing the grid in remote areas, or increasing the transmission capability of long overhead lines. One relatively new application for SVC is voltage control at the point of common coupling for offshore wind farms, being connected to the grid by AC submarine cables. SVC PLUS®is perfectly suited to this task, as the long list of projects awarded to Siemens shows. The first application has been the Thanet project in UK, commissioned in 2009 and delivering 2x ±35 MVAr in a container based standard solution, see Fig. 5. Another eleven SVC PLUS® containers for grid access of offshore wind farms have been currently commissioned, each providing ±50 MVAr. The Kikiwa project for Transpower, NZ was commissioned in 2010, fulfilling strong undervoltage requirements. In the meantime, this customer ordered another SVC PLUS® project, giving even some more confidence in the good performance of this innovative product.cooling system converter control& protectionFig. 5: Standard container arrangement of SVC PLUS®HVDC projects in executionOffshore wind farms at a distance of more than around 70 km need a HVDC connection to the grid. The offshore HVDC station must be able to generate a three phase voltage to start up the wind farm, referred to as “black-start capability”. For this reason, only VSC schemes have been taken into account for the connection of remote wind farms in the North Sea. By May 2011, with its HVDC PLUS® technology, Siemens has been able to win three out of five projects, see Fig. 6 for locations and technical data. With power ratings between 576 MW and 864 MW and the demanded fault ride through capability these projects certainly have set the pace of development, and they gave the final boost to the MMC technology.Alongside with the converter development for high power offshore applications, the other elements needed for this special application are under development. The cooling system may be mentioned here, the transformer configuration avoiding the risk of long downtimes after a fault, the space-saving switchgear equipment and last, but not least, the huge offshore platform itself, see the WIPOS® sketch in Fig. 6. The three projects mentioned will go into service in the years 2013 and 2014.Another highlight of the MMC development is the INELFE project, creating an additional connection between France and Spain. A 60 km pair of cables will be used for this link, partly installed in a tunnel under the Pyrenees. Here, the low losses, the excellent dynamic behaviour and the black start capability played a decisive role on the way to win this project for Siemens. The voltages are 400 kV on the AC sides and 320 kV on the DC side. With a transmission power of 2x 1000 MW this marks a new record for HVDC PLUS® and for VSC technology in general.Challenges aheadMMC development has really taken big leaps in the last years, but certainly this has not come to an end. The power ratings will go up, in the long run leaving only the high end power ratings and the Ultra High Voltage sector for the LCC technology. Improved control features like negative phase sequence compensation or damping of harmonics will be introduced. Looking at the big picture, HVDC will develop from isolated point-to-point connections to being an integrative part of future overlay grids. Multi terminal systems will be the next step on this road.In these wide-area overlay grids, the following items need special attention:•Power flow control•Interference of multiple AC and DC systems•Increasing portion of converter based generation and consumption in the grids. For example, there will be “super nodes” connecting multiple wind farms and HVDC lines, without anyconventional generation involved.•Integration of energy storage systems•Maintaining a proper selectivity, converter or line faults have to be isolated very fastThese challenges have to be addressed bearing in mind that interconnected systems have to be expandable und upgradeable to meet future demands, and they have to be multi-vendor systems. Of course, all innovations have to meet the high level of availability that customers already know from their LCC equipment for HVDC and FACTS.Fig. 6: Offshore projects in the North Sea awarded to SiemensConclusionThe power transmission and distribution grids will go through rapid changes in the next years, due to the high amount of renewable energy sources to be integrated. This trend obviously applies to Europe and North America, but it’s not limited to these parts of the world. For example, China has also started a wind energy program, and others will follow.HVDC and FACTS equipment will play a vital role in the development of the grids; they represent the “smart” capabilities in the medium and high voltage area. HVDC stations do not just transmit active power and FACTS installations do not just add reactive power – they are additionally used for multiple stabilizing and damping functions. For example, HVDC connections act as a “firewall” against electric disturbances spreading out in the grid.Self-commutated converters offer advantages over the classical line commutated converters – they can act faster, a VSC based HVDC station can adjust active and reactive power independently from each other. With the introduction of the modular multilevel converter, the VSC technology has been improved decisively, now offering the same efficiency as thyristor-based converters in conjunction with a superb dynamic performance. Due to these advantages, the modular multilevel converter market share will grow even faster than the HVDC and FACTS market in general.。
