电气工程毕业论文外文翻译

文库168有毕业设计外文翻译 很多

自己先找一篇中文的，再在网上用有道或其它网站的人工翻译翻译一下，也就付个一点钱，还是挺值的。 有篇中文的，自己去翻译。

Control of Parallel Inverters in Distributed AC Power Systems with Consideration of Line Impedance Effect在分布式交流电力系统中考虑连线阻抗影响时的并联逆变器控制 论文发到你的邮箱了

你学校图书馆的英文数据裤里面肯定有，你找找看，本科的外文翻译 要求不高 基本没人看

论文中英对照，可能有错误，但应该不会很多。概述： Overview: 电气工程及其自动化的触角伸向各行各业，小到一个开关的设计，大到宇航飞机的研究，都有它的身影。 Electrical Engineering and Automation tentacles all walks of life, small to a switch designed to study aerospace aircraft, has its shadow. 本专业生能够从事与电气工程有关的系统运行、自动控制、电力电子技术、信息处理、试验技术、研制开发、经济管理以及电子与计算机技术应用等领域的工作，是宽口径“复合型”高级工程技术人才。 Health professionals can be engaged in the electrical engineering and operation of the system, automatic control, power electronics technology, information processing, testing technology, research and development, economic management, and electronic and computer technology applications in areas such as the work is宽口径"compound" High engineering and technical personnel. 该领域对高水平人才的需求很大。 High-level talents in the field of high demand. 据估计，随着国外大企业的进入，在这一专业领域将出现很大缺口，那时很可能出现人才供不应求的现象。 It is estimated that with the entry of large foreign enterprises in the fields of expertise will be a big gap, then there is likely to personnel shortage. 一、专业综合介绍 First, a synthesis of professional 电气工程及其自动化专业是电气信息领域的一门新兴学科，但由于和人们的日常生活以及工业生产密切相关，发展非常迅速，现在也相对比较成熟。 Electrical Engineering and Automation of electrical information professional is an emerging field of science, but because of people's daily lives and industrial production is closely related to the extraordinarily rapid development of relatively more mature now. 已经成为高新技术产业的重要组成部分，广泛应用于工业、农业、国防等领域，在国民经济中发挥着越来越重要的作用。 High-tech industry has become an important component of the widely used in industry, agriculture, national defense and other fields, in the national economy is playing an increasingly important role. 控制理论和电力网理论是电气工程及自动化专业的基础，电力电子技术、计算机技术则为其主要技术手段，同时也包含了系统分析、系统设计、系统开发以及系统管理与决策等研究领域。 Control theory and electrical network theory is a professional electrical engineering and automation of the base, power electronics technology, computer technology is its main technical means, but also includes a system analysis, system design, system development and system management and decision-making research. 该专业还有一些特点，就是强弱电结合、电工电子技术相结合、软件与硬件相结合，具有交叉学科的性质，电力、电子、控制、计算机多学科综合，使毕业生具有较强的适应能力，是“宽口径”专业。 There are some characteristics of the profession, that is, combining the strength of power, electrical and electronic technology, software and hardware combined with a cross-disciplinary nature, electricity, electronics, control, computer integrated multi-disciplinary, so that graduates with strong adaptation capacity, is "宽口径" professional. 电气工程及其自动化专业对广大考生有很强的吸引力，属于热门专业，高考录取分数线往往要比其他专业方向高许多，造成这一情况的主要原因有：①就业容易，工作环境好，收入高；②名称好听，专业内容对学生有吸引力； 社会宣传和舆论导向对其有利。 Electrical Engineering and Automation of the majority of candidates have a strong appeal, are popular professional, college entrance examination admission than is often high in many other professional direction, resulting in the situation of the main reasons: ① job easier, a good working environment, income high; ② the name of good, professional content attractive to students; social advocacy and public opinion in his favor. 该专业方向有着非常好的发展前景，研究成果较容易向现实产品转换，而且效益相当可观。 The direction of the profession has a very good development prospects, research products more easily converted to reality, and considerable benefits. 他创造性的研究思路吸引着众多考生，这里的确是展示他们才能的好地方。 His research and creative ideas to attract a large number of candidates, where they can really show a good place. 但是鉴于国内现在的形式，考生在报考该专业的时候应该注意以下两点： However, in view of the domestic form of the present candidates in time to apply the profession should pay attention to the following two points: (1)充分考虑自己的兴趣。 (1) give full consideration to their interests. 也许自己本来并不对该方向感兴趣，但是许多人都说好，于是自己就“感兴趣”了。 Perhaps their interest was not the direction, but many people say that good, so they are "interested in" the. 这对以后的发展是很不利的，毕竟兴趣是最好的老师。 This future development is very negative, after all, interested in is the best teacher. (2)衡量自己的综合素质。 (2) to measure the overall quality of their own. 电气工程及自动化专业需要具有扎实的数学、物理基础，较强的外语综合能力，为今后能够掌握并且灵活运用专业知识做准备。 Electrical engineering and automation with a solid professional needs of mathematics, physics basis for a strong comprehensive foreign language capabilities, for future flexibility in the use of and access to expertise to prepare. 该专业方向的人才需求虽然大，但可供选择的人也很多，如果没有非常强的综合素质，很难在众人之中脱颖而出，取得突出成绩。 The demand for professional talent while the direction, but to choose a lot of people, if there is no overall quality is very strong, it is difficult to stand out among the people, have achieved outstanding results. 也许这对许多胸怀远大志向的考生来说是不能接受的。 This may cherish lofty aspirations of many of the candidates is unacceptable. 当然，这里所说的两点是否可行也和学生个人的追求有关，如果一个人追求仅限于一份较好的工作，该专业的确是一个不错的选择。 Of course, the two points mentioned here and also the feasibility of the pursuit of individual students, and if a person is limited to the pursuit of a better work, the profession is indeed a good choice. 但是，如果想在科技创新方面做出突破性的贡献还是要建立在个人实力以及刻苦努力的基础上，馅饼是决不会无缘无故从天上掉下来的。 However, if you want to make a breakthrough in scientific and technological innovation or contribution to the establishment of personal strength and hard work on the basis of the pie for no reason at all will not come knocking on the door. 由于本专业研究范围广，应用前景好，毕业生的专业素养相对较高，因此就业形势非常好。 Because of this wide range of professional research, applications, and professional graduates is relatively high, so the employment situation is very good. 我国现在非常需要该专业方向的人才，小到一个家庭，大到整个社会，都离不开这些专业人才的工作。 Our country is now a great need for the direction of the professional personnel, as small as a family as large as the whole community can not be separated from the work of these professionals. 通常情况下，学生毕业后可以选择国有的质量技术监督部门、研究所、工矿企业等；也可以是一些外资、私营企业，待遇当然是相当可观的。 Under normal circumstances, students can choose the state after graduating from the quality and technology supervision department, research institutes, industrial and mining enterprises, etc.; also can be a number of foreign investment, the private sector, the treatment is considerable. 如果学生能力足够强，又在学习期间积累了比较好的研究成果，完全可以自己创业，闯出一片属于自己的天空。 If enough students, and also in the learning accumulated during the relatively good results, can be our own business, break a piece of the sky belongs to them. 需要指出的是，由于国外在该专业方向的研究要领先于我们，因此如果想要有进一步的发展，确立自己在国内该方向的领先地位，出国深造是一个不错的选择。 It should be noted that as a result of foreign professionals in the direction of research should lead us, so if you want to have further development, and identify their roles in the domestic leading position in that direction, go abroad for further study is a good choice. 电气工程及其自动化专业代码：080601。 Electrical Engineering and Automation code: 080601. 二、专业教育发展状况 Second, the development of professional education 电气工程与自动化专业是理、工、文相结合，融机械工程、艺术学和计算机设计于一体的新型交叉学科专业之一。 Electrical Engineering and Automation is the science, engineering, the combination of financial engineering, art and computer design in one of the new cross-disciplinary professionals. 主干学科包括电子工程、计算机科学与技术、控制科学与工程。 Backbone of disciplines, including electrical engineering, computer science and technology, control science and engineering. 本专业产生于70年代，首先在英国的牛津大学，首次实现的是直流电的控制方式，那时候执行元件的驱动电压是直流的，控制电压也是直流的，自动化系统的工作方式是很简单、粗糙的，精度也很低。 Resulting in 70 of the professional era, first of all, the Oxford University in England, the first time that the DC control, then the implementation of components of the drive voltage is a DC control voltage is DC, the automation system is very simple, rough accuracy is very low. 但直流的控制方式由于其历史的久远而被人们所熟知，自然而然的人们想到了用直流电去控制交流执行元件。 However, the control of DC because of its long history has been well-known people, people naturally think of using the DC component to control the exchange of implementation. 随着晶体管、大功率晶体管、场效应管等大功率的电子器件的出现和成熟、以及建立在场的理论上、以现代数学、矩阵代数为理论依据的弱电强电控制系统更使电子技术与自动化达到新的历史高度。 With the transistor, high-power transistors, FET high-power electronic devices, such as the emergence and maturity, as well as the establishment of the presence of the theory, modern mathematics, matrix algebra of the weak theoretical basis for the strong electrical control system of electronic technology and automation to reach a new historical high. 至此，本专业得到了广泛的发展，日本、美国、英国及其他国家的大学也纷纷设立了本专业，在这一时期的成果也并不少，诸如完成数控机床，车间厂房自动控制的工作已经是新的课题。 So far, this has been a wide range of professional development, Japan, the United States, Britain and other countries have also established the University of the professional, the results during this period and also quite a few, such as the completion of CNC machine tools, factory automation work shop is a new topic. 电子技术与自动化、计算机的有机结合，赋予电子工程及自动化专业以全新的内涵。 Electronic technology and automation, the organic integration of computer, electronic engineering and automation to give a new meaning of professional. 无人操纵，系统简化，格局合理，即插即用型的产品成为新宠。 No manipulation, the system simplified, reasonable structure, plug-and-play products to become the new darling. 建国初期（1949—1966）我国许多大学设立了本专业，主要实践性教学环节包括电路与电子技术实验、电子工艺实习、金工实习课程设计、生产实习、毕业设计，并为国家培养了许多的这方面人才。 The founding of the early (1949-1966) established in many universities in this profession, the main practice teaching links include the experimental circuit and electronics technology, electronics technology training, curriculum design metalworking practice, production internships, graduate, and the culture of many countries in this fields. 他们已成为本行业的专家学者，分布在我国许多省、市，成为骨干力量。 They have become the industry experts and scholars in China's many provinces, cities and become the backbone of. “文革”期间，由于受政治的影响，全国的高等院校相继停止招生，本专业受到了很大的影响，先是老师被批斗，后来学校根本办不下去了，只能停止招生。 "Cultural Revolution" period, because of political influence, the country's institutions of higher learning have to stop recruitment, the professional has been a great impact, first teacher was criticized and denounced, and later run schools do not go on, only to stop enrollment. 但是，即便如此，许多老师并没有停止研究。 But even so, many teachers did not stop the research. 他们知道电子工程及自动化对我国的现代化建设起重要的作用，因而，在这一时期，并没有放弃对专业的研究和探索。 They know that in electrical engineering and automation of the modernization of China's important role to play, which, in this period, and did not give up on the professional research and exploration. 改革开放以后，在党中央的正确领导下，大学恢复了招生，本专业也发展起来，许多大学设立了本专业，并陆续招生，每年为国家培养大量的高级复合型人才，包括学士、博士等高级知识分子，特别是目前，各专业扩招，本专业的招生量也在上升。 After reform and opening-up in under the correct leadership of the CPC Central Committee, the University Admissions restored, the profession has developed, many universities set up a professional, and have students trained each year a large number of high-level compound talents, including the degree, Dr. intellectuals, especially, expansion of the professional, the professional capacity of students is also rising. 虽然我国在这方面的发展还没有站在世界的最前沿，但随着我国综合国力的提高，对外交往的增加，我们已经逐渐缩小与发达国家的差距。 Although China's development in this area is also not on the side of the world's most cutting-edge, but with the improvement of China's overall national strength, the increase in foreign exchanges, we have gradually narrowed the gap with the developed countries. 具有代表性的是：每秒3000亿次计算机研制成功；纳米技术的掌握；模拟技术的应用。 Representative is: 300 billion times per second, the successful development of a computer; nano-technology to master; simulation technology. 一个不容忽视的问题摆在我们面前：如何迎接新技术革命的挑战？ A problem that can not be ignored before us: how to meet the challenges of the new technological revolution? 经过本专业的老师和同学的共同努力，把电子工程及自动化专业拓展开来，分为“电力系统及其自动化”和“电子信息工程”，涵盖原有“绝缘技术”、“电气绝缘与电缆”、“电机电器及其控制”、“电气工程及其自动化”、“应用电子技术”和“光源与照明”等几个专业方向。 After the professional efforts of teachers and students to electrical engineering and automation professions open to expand into, "Power System and Automation" and "Electronic and Information Engineering", covering the original "insulation technology", "Electrical Insulation and cable "," Electric Motor and Control "," Electrical Engineering and Automation, "" the application of electronic technology "and" light and lighting, "and several other professional direction. 设有“高电压与绝缘技术”、“电机与电器”、“电力电子与电力传动”和“电工理论与新技术”、“高电压与绝缘技术”博士学位方向。 With "High Voltage and Insulation Technology", "Electric Machines and Electric", "Power Electronics and Electric Power Transmission" and "electrical theory and new technology", "High Voltage and Insulation Technology" doctorate direction. 并以工业产品设计为基础，应用计算机造型、设计、实现工业产品的结构、性能、加工、外形等的设计和优化。 And the design of industrial products based on the application of computer modeling, design, realization of the structure of industrial products, performance, processing, shape and other design and optimization. 该专业培养适应社会急需的，既有扎实科学技术基础又有艺术创新能力的高级复合型技术人才。 The professional training needed to adapt to society, both based on solid scientific and technological innovation capability and high-level art composite technology. 本专业着重培养学生外语、计算机应用、产品造型、设计等实际工作能力，实现平面设计、立体设计等产品设计的全面智能化。 Focus on the professional training of students in foreign languages, computer applications, product modeling, design of practical work, such as the ability to achieve graphic design, three-dimensional design, product design, intelligent all-round. 该专业毕业生可从事工业产品造型设计、计算机应用、视觉传达设计、环境设计、广告创意、企业形象策划等行业的教学、科研、生产、开发和管理工作。 The graduates can be engaged in industrial product design, computer applications, visual communication design, environmental design, advertising creative, corporate image planning, such as industry, teaching, scientific research, production, development and management. 囊括了电路原理、电子技术基础、电机学、电力电子技术、电力拖动与控制、计算机技术（语言、软件基础、硬件基础、单片机等）、信号与系统、控制理论等课程。 Include circuit theory, electronic and technological base, and electric machinery, power electronics, electric drive and control, computer technology (languages, software infrastructure, hardware, microcontroller, etc.), signals and systems, control theory and so on. 高年级还根据社会需要学习柔性的、适应性强、覆盖面宽的专业课及专业选修课。 High-grade based on the needs of the community to learn flexibility, adaptability, wide coverage of elective courses and professional. 同时也进行电机与控制实验、电子工程系统实验、电力电子实验等。 At the same time also the experimental and control the electrical and electronic engineering experiments, such as power electronics experiments. 一直以来，我国在CIMS，自动控制，机器人产品，专用集成电路等等方面有了长足的进步。 All along, our CIMS, automatic control, robotics products, application specific integrated circuit and so on has made substantial progress. 例如：“基于微机环境的集成化CAPP应用框架与开发平台”开发了以工艺知识库为核心的、以交互式设计模式为基础的综合智能化CAPP开发平台与应用框架（CAPPFramework），推出金叶CAPP、同方CAPP等系列产品。 For example: "Computer-based integrated environment CAPP application framework and development platform" to develop a knowledge base as the core technology to interactive design based on the model of the integrated intelligent CAPP development platform and application framework (CAPPFramework), the introduction of Golden CAPP, with CAPP and other side products. 具有支持工艺知识建模和动态知识获取、各类工艺的设计与信息管理、产品工艺信息共享、支持特征基创成工艺决策等功能，并提供工艺知识库管理、工艺卡片格式定义等应用支持工具和二次开发工具。 With the support process modeling and dynamic knowledge of knowledge acquisition, the design of various types of technology and information management, product process information sharing in support of the characteristics of generative process-based decision-making functions, and provide technology Knowledge management, technology applications such as card format support of the definition of tools and secondary tools. 系统开放性好，易于扩充和维护。 System openness, and easy expansion and maintenance. 产品已在全国的企业，特别是CIMS示范工程企业，推广应用，还研制了自动控制装置及系列产品，红外光电式安全保护装置，大功率、高品质开关电源的开发。 Products have been in the country's enterprises, especially enterprises CIMS demonstration project to promote the application, as well as the development of the automatic control devices and products, infrared photoelectric safety protection device, high power, high-quality switching power supply development. 机器人产品包括移动龙门式自动喷涂机，电动喷涂机器人，柔性仿形自动喷涂机，往复式喷涂机，自动涂胶机器人，框架式机器人，搬运机器人，弧焊机器人的研制。 Products include mobile gantry robot automatic spraying machine, electric spraying robot, flexible profiling automatic spraying machine, reciprocating spray machines, automatic coating robots, robot frame, handling robots, welding robot. 以上这些产品的开发应用还只是电子工程与自动化在生产中的一个侧面，不足以反映其全貌。 Over the development and application of these products are only in electrical engineering and automation in the production of one aspect does not adequately reflect the full picture. 在国外先进技术的冲击下，从各个方面进行新一轮技术重组。 In the impact of foreign advanced technology from all aspects of the reorganization of a new round of technology. 形势是严峻的，同时也充满机遇。 The situation is serious, but also full of opportunities.

我有一篇我本科毕设的小论文，英文中文都有，而且是我人工翻译的，8000字左右。你要的话PM我。我是电气工程及其自动化专业的。《Analysis of thyristor-controlled phase shifter applied in damping power system oscillations》

用于分布式在线UPS中的并联逆变器的一种无线控制器A Wireless Controller for Parallel Inverters in Distributed Online UPS SystemsJosep M. Guerrero', Luis Garcia de Vicufia", Jose Matas'*, Jaume Miret", and Miguel Castilla". Departament #Enginyeria de Sistemes, Automatica i Informhtica Industrial. Universitat Polithica de CatalunyaC. Comte d'Urgell, 187.08036 -Barcelona. Spain. Email: .. Departament #Enginyeria Electrbnica. Universitat Polit6cnica de CatalunyaAV. Victor BaLguer s/n. 08800I - Vilanova i la Geltrh. SpainAbsiract - In this paper, a novel controller for parallelconnectedonline-UPS inverters without control wireinterconnections is presented. The wireless control technique isbased on the well-known droop method, which consists inintroducing P-oand Q-V schemes into the inverters, in order toshare properly the power drawn to the loads. The droop methodhas been widely used in applications of load sharing betweendifferent parallel-connected inverters. However, this methodhas several drawbacks that limited its application, such as atrade-off between output-voltage regulation and power sharingaccuracy, slow transient response, and frequency and phasedeviation. This last disadvantage makes impracticable themethod in online-UPS systems, since in this case every modulemust be in phase with the utility ac mains. To overcome theselimitations, we propose a novel control scheme, endowing to theparalleled-UPS system a proper transient response, strictlyfrequency and phase synchronization with the ac mains, andexcellent power sharing. Simulation and experimental resultsare reported confirming the validity of the proposed approach.1. INTRODUCTIONThe parallel operation of distributed Uninterruptible PowerSupplies (UPS) is presented as a suitable solution to supplycritical and sensitive loads, when high reliability and poweravailability are required. In the last years, many controlschemes for parallel-connected inverters has been raised,which are derived from parallel-schemes of dc-dc converters[I], such as the master-slave control [2], or the democraticcontrol [3]. In contrast, novel control schemes have beenappeared recently, such as the chain-structure control [4], orthe distributed control [ 5 ] . However, all these schemes needcontrol interconnections between modules and, hence, thereliability of the system is reduced since they can be a sourceof noise and failures. Moreover, these communication wireslimited the physical situation ofthe modules [6].In this sense, several control techniques has been proposedwithout control interconnections, such as the droop method.In this method, the control loop achieves good power sharingmaking tight adjustments over the output voltage frequencyand amplitude of the inverter, with the objective tocompensate the active and reactive power unbalances [7].This concept is derived from the power system theory, inwhich the frequency of a generator drops when the powerdrawn to the utility line increases [8].0-7803-7906-3/03/$17.00 02003 IEEE. 1637However, this control approach has an inherent trade-offbetween voltage regulation and power sharing. In addition,this method exhibits slow dynamic-response, since it requireslow-pass filters to calculate the average value of the activeand reactive power. Hence, the stability and the dynamics ofthe whole system are hardly influenced by the characteristicsof these filters and by the value of the droop coefficients,which are bounded by the maximum allowed deviations ofthe output voltage amplitude and frequency.Besides, when active power increases, the droopcharacteristic causes a frequency deviation from the nominalvalue and, consequently, it results in a variable phasedifference between the mains and the inverter output voltage.This fact can be a problem when the bypass switch mustconnect the utility line directly to the critical bus in stead ofits phase difference. In [9], two possibilities are presented inorder to achieve phase synchronization for parallel lineinteractiveUPS systems. The first one is to locate a particularmodule near the bypass switch, which must to synchronizethe output voltage to the mains while supporting overloadcondition before switch on. The second possibility is to waitfor the instant when phase matching is produced to connectthe bypass.However, the mentioned two folds cannot be applied to aparallel online-UPS system, since maximum transfer timeought to be less than a % of line period, and all the modulesmust be always synchronized with the mains when it ispresent. Hence, the modules should be prepared to transferdirectly the energy from the mains to the critical bus in caseof overload or failure [lo].In our previous works [11][12], we proposed differentcontrol schemes to overcome several limitations of theconventional droop method. However, these controllers bythemselves are inappropriate to apply to a parallel online-UPS system. In this paper, a novel wireless control scheme isproposed to parallel different online UPS modules with highperformance and restricted requirements. The controllerprovides: 1) proper transient response; 2) power sharingaccuracy; 3) stable frequency operation; and 4) good phasematching between the output-voltage and the utility line.Thus, this new approach is especially suitable for paralleled-UPS systems with true redundancy, high reliability andpower availability. Simulation and experimental results arereported, confirming the validity of this control scheme.Fig. 1. Equivalenl cimuif ofan invener connecled 10 a bust"Fig. 2. P-odraop function.11. REVlEW OF THE CONVENTIONAL DROOP METHODFig. 1 shows the equivalent circuit of an inverter connectedto a common bus through coupled impedance. When thisimpedance is inductive, the active and reactive powers drawnto the load can be expressed asEVcosQ - V2 Q=where Xis the output reactance of an inverter; Q is the phaseangle between the output voltage of the inverter and thevoltage of the common bus; E and V are the amplitude of theoutput voltage of the inverter and the bus voltage,respectively.From the above equations it can be derived that the activepower P is predominately dependent on the power angle Q,while the reactive power Q mostly depends on the outputvoltageamplitude. Consequently, most of wireless-control ofparalleled-inverters uses the conventional droop method,which introduces the following droops in the amplitude Eand the frequency U of the inverter output voltageu = w -mP (3)E = E ' - n Q , (4)being W* and E' the output voltage frequency and amplitudeat no load, respectively; m and n are the droop coefficientsfor the frequency and amplitude, respectively.Furthermore, a coupled inductance is needed between theinverter output and the critical bus that fixes the outputimpedance, in order to ensure a proper power flow. However,it is bulky and increase:; the size and the cost of the UPSmodules. In addition, tho output voltage is highly distortedwhen supplying nonlinezr loads since the output impedanceis a pure inductance.It is well known that if droop coefficients are increased,then good power sharing is achieved at the expense ofdegrading the voltage regulation (see Fig. 2).The inherent trade-off of this scheme restricts thementioned coefficients, which can be a serious limitation interms of transient response, power sharing accuracy, andsystem stability.On the other hand, lo carry out the droop functions,expressed by (3) and (4), it is necessary to calculate theaverage value over one line-cycle of the output active andreactive instantaneous power. This can be implemented bymeans of low pass filters with a smaller bandwidth than thatof the closed-loop inverter. Consequently, the powercalculation filters and droop coefficients determine, to a largeextent, the dynamics and the stability of the paralleledinvertersystem [ 131.In conclusion, the droop method has several intrinsicproblems to be applied 1.0 a wireless paralleled-system ofonline UPS, which can he summed-up as follows:Static trade-off between the output-voltage regulation(frequency and amplitude) and the power-sharingaccuracy (active an4d reactive).2) Limited transient response. The system dynamicsdepends on the power-calculation filter characteristics,the droop coefficients, and the output impedances.Lost of ac mains synchronization. The frequency andphase deviations, due to the frequency droop, makeimpracticable this method to a parallel-connectedonline UPS system, in which every UPS should becontinuously synchronized to the public ac supply.1)3)111. PROPOSED CONTROL FOR PARALLEL ONLINE UPSINVERTERSIn this work, we will try to overcome the above limitationsand to synthesize a novel control strategy withoutcommunication wires that could be appropriate to highperformanceparalleled industrial UPS. The objective is toconnect online UPS inverters in parallel without usingcontrol interconnections. This kind of systems, also namedinverter-preferred, should be continuously synchronized tothe utility line. When an overload or an inverter failureoccurs, a static bypass switch may connect the input line tothe load, bypassing the inve:rter [14][15].Fig. 3 shows the general diagram of a distributed onlineUPS system. This system consists of two buses: the utilitybus, which is connected lo the public ac mains; and thesecure bus, connected to the distributed critical loads. Theinterface between these buses is based on a number of onlineUPS modules connected in parallel, which providescontinuously power to the: loads [16]. The UPS modulesinclude a rectifier, a set of batteries, an inverter, and a staticbypass switch.11638Q ac mainsutility busI I Ij distributed loads !Fig. 3. Online distributed UPS system.syposr /I 4(4Fig. 4. Operation modes of an online UPS.(a) Normal operation. (b) Bypass operation. (c) Mains failureThe main operation modes of a distributed online UPS1) Normal operation: The power flows to the load, fromthe utility through the distributed UPS units.2) Mains failure: When the public ac mains fails, theUPS inverters supply the power to the loads, from thebatteries, without disruption.Bypass operation: When an overload situation occurs,the bypass switch must connect the critical busdirectly to the ac mains, in order to guarantee thecontinuous supply of the loads, avoiding the damageof the UPS modules.For this reason, the output-voltage waveform should besynchronized to the mains, when this last is present.system are listed below (see Fig. 5):3)Nevertheless, as we state before, the conventional droopmethod can not satisfy the need for synchronization with theutility, due to the frequency variation of the inverters, whichprovokes a phase deviation.To obtain the required performance, we present a transientP-w droop without frequency-deviation in steady-state,proposed previously by OUT in [ 111w=o -mP (5)where is the active power signal without the dccomponent,which is done by. -I t -1sP= p ,( s + t - ' ) ( s + o , )being zthe time constant of the transient droop action.The transient droop function ensures a stable frequencyregulation under steady-state conditions, and 'at the sametime, achieves active power balance by adjusting thefrequency of the modules during a load transient. Besides, toadjust the phase of the modules we propose an additionalsynchronizing loop, yieldingo=w'-m%k,A$, (7)where A$ is the phase difference between the inverter and themains; and k, is the proportional constant of the frequencyadjust. The steady-state frequency reference w* can beobtained by measuring the utility line frequency.The second term of the previous equality trends to zero insteady state, leading tow = w' - k4($ -@'), (8)being $and $* the phase angles of the output voltage inverterand the utility mains, respectively.Taking into account that w = d $ / d t , we can obtain thenext differential equation, which is stable fork, positived$ *dt dt- + km$ = - + k,$' . (9)Thus, when phase difference increases, frequency willdecrease slightly and, hence, all :he UPS modules will besynchronized with the utility, while sharing the power drawnto the loads.IV. CONTROLLIEMRP LEMENTATIONFig. 5 depicts the block diagram of the proposedcontroller. The average active power P , without the dccomponent, can be obtained by means of multiplying theoutput voltage by the output current, and filtering the product........................................................................................io",.LSj'nchronirorion loop.......................................................................................Fig. 5. Block diagram of the proposed controller.using a band-pass filter. In a similar way, the averagereactive power is obtained, hut in this case the output-voltagemust be delayed 90 degrees, and using a low-pass filter.In order to adjust the output voltage frequency, equation(7) is implemented, which corresponds to the frequencymains drooped by two transient-terms: the transient activepower signal term; and the phase difference term, whichis added in order to synchronize the output voltage with theac mains, in a phase-locked loop (PLL) fashion. The outputvoltageamplitude is regulated by using the conventionaldroop method (4).Finally, the physical coupled inductance can be avoided byusing a virtual inductor [17]. This concept consists inemulated an inductance behavior, by drooping the outputvoltage proportionally to the time derivative of the outputcurrent. However, when supplying nonlinear loads, the highordercurrent-harmonics can increase too much the outputvoltageTHD. This can be easily solved by using a high-passfilter instead of a pure-derivative term of the output current,which is useful to share linear and nonlinear loads [I 1][12].Furthermore, the proper design of this output inductance canreduce, to a large extent, the unbalance line-impedanceimpact over the power sharing accuracy.v. SIMULATION AND EXPERIMENTARELS ULTSThe proposed control scheme, (4) and (7), was simulatedwith the parameters listed in Table 1 and the scheme shownin Fig. 6, for a two paralleled inverters system. Thecoefficients m, n, T, and kv were chosen to ensure stability,proper transient response and good phase matching. Fig. 7shows the waveforms of the frequency, circulating currents,phase difference between the modules and the utility line,and the evolution of the active and reactive powers. Note theexcellent synchronization between the modules and theACmiiinr 4 j. ...L...I.P...S...1... ..........................B...u...n...r.r..r..e..s... ................................... iFig. 6. Parallel operation oftwa online UPS modules,mains, and, at the same time, the good power sharingobtained. This characteristik let us to apply the controller tothe online UPS paralleled systems.Two I-kVA UPS modules were built and tested in order toshow the validity of the proposed approach. Each UPSinverter consisted of a single-phase IGBT full-bridge with aswitching frequency of 20 kHz and an LC output filter, withthe following parameters: 1. = 1 mH, C = 20 WF, Vi" = 400V,v, = 220 V, I50 Hz. The controllers of these inverters werebased on three loops: an inner current-loop, an outer PIcontroller that ensures voltage regulation, and the loadsharingcontroller, based on (4) and (7). The last controllerwas implemented by means of a TMS320LF2407A, fixedpoint40 MHz digital sigrial processor (DSP) from TexasInstruments (see Fig. 8), using the parameters listed in TableI. The DSP-controller also includes a PLL block in order tosynchronize the inverter with the common bus. When thisoccurs, the static bypass switch is tumed on, and the droopbasedcontrol is initiated.1640big 7 Wa\cfc)rms for twu.invencr, ;mnectcd in parallel. rpchrontred io Ihc ac mdnl.(a) Frequencics ufhoth UPS (b) Clrculattng currcni among modulcs. (CJ Phmc d!Nercn;: betucen ihc UPS a#>dth e ai mum(d) Ikiril uf the phze diNmncc (e) md (0 Activc and rcactlw pouerr "I ooih UPSNote that the iimc-acs arc deliheratcly JiNercni due in thc disiinct timuion*uni) ofthe \ inrblrr1641TABLEI.PARAMETEROSF THE PARALLELESDYS TEM.Filter Order I IFilter Cut-off Frequency I 0, I 10 I ragsFig. 8 shows the output-current transient response of theUPS inverters. First, the two UPS are operating in parallelwithout load. Notice that a small reactive current is circlingbetween the modules, due to the measurement mismatches.Then, a nonlinear load, with a crest factor of 3, is connectedsuddenly. This result shows the good dynamics and loadsharingof the paralleled system when sharing a nonlinearload.Fig. 8. Output current for the two paralleled UPS, during the connection of Bcommon nonlinear load with a crest factor of 3. (Axis-x: 20 mddiv. Axis-y:5 Mdiv.).VI. CONCLUSIONSIn this paper, a novel load-sharing controller for parallelconnectedonline UPS systems, was proposed. The controlleris based on the droop method, which avoids the use ofcontrol interconnections. In a sharp contrast with theconventional droop method, the controller presented is ableto keep the output-voltage frequency and phase strictlysynchronized with the utility ac mains, while maintaininggood load sharing for linear and nonlinear loads. This fact letus to extend the droop method to paralleled online UPS.On the other hand, the proposed controller emulates aspecial kind of impedance, avoiding the use of a physicalcoupled inductance. Th.e results reported here show theeffectiveness of the proposed approach.