关于电气英文论文题目

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

电力是发展生产和提高人类生活水平的重要物质基础，电力的应用在不断深化和发展，电气自动化是国民经济和人民生活现代化的重要标志。学术堂整理了十五个电气工程论文题目供大家进行参考：1、短路电流计算曲线的算法研究及与IEC短路电流计算法的对比2、计算曲线法用于大容量机组短路电流计算的评估3、崇明电网配置低压减载装置的必要性和可行性研究4、电压稳定计算中配网模型的研究5、上海电网电压稳定极限运行能力分析6、发电机励磁系统模型对短路电流计算结果的影响7、联络线功率对上海电网电压稳定极限运行的影响8、采用“干预法”估计谐波阻抗9、波过程试验装置的研制10、直流电源中可控硅控制电路的设计11、应用于波过程试验装置的频率可调方波发生器的研制12、水位测量仪的液晶显示器电路的设计13、基于R232、R485的无线数据通信系统的设计14、直流电源中脉冲宽度控制电路的设计15、红外温度测试系统中数据采集电路的设计

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.

不会写论文还这么嚣张?不就是250分吗得到了又怎么地？能吃呀？

1 距离保护（ZM1-5）1.1 情况 概述距离保护装置是在输电网和变电网中应用得最广泛的一种保护装置。在配电网中它也变得越来越重要。主要原因如下：*它在线路两端之间的通信通道中的独立性，是因为它是利用本地有效电流和电压信息动作的。*距离保护在电力网中形成了一个相互关联的有选择性的保护系统（非单元式的保护系统）。这意味着它也可以作为网络中其他主要元件的远后备保护。现代线路保护的基本要求，比如快速性，灵敏性和选择性，以及在可靠性和安全性方面的严格要求，变得越来越严格。另外，现代距离保护在网络中必须能够与阻抗继电器配合动作，这是一种由不同技术设计而成的继电器（静态或者是机电式继电器）。较早的阻抗继电器在多数情况下只用于电力线路的相间和三相故障的保护，一些其他保护用于接地故障中。由于这些原因现代距离保护的灵活性非常重要，当它用于一个复杂的网络结构时尤其合适。比如并列运行的多回线路和辐射网。距离保护的有选择性动作不是依靠线路两端间的通信设备。距离保护能在远方末端电流互感器处检测到故障。这个功能使它成为那些不能检测到超过反方向末端电流互感器范围以外故障的线路差动保护的一个理想补偿。距离保护范围在线路REX 5XX的保护、控制和终端监测方面的距离保护装置由3到5个独立的距离保护范围组成，每一个包括了3个接地故障的测量元件和3个相间故障的测量元件。对于各种不同电压等级在不同的电网中，不同的终端要适合不同的要求。由于这个原因，距离保护装置的一些特征参数各终端之间是不同的（要了解详细内容，请查阅线路保护终端的分类细节）。距离保护区域5不同于其他段在于它动作的快速性。它比其他距离保护段启动快，而且在不同的系统暂态过程中，由于这个原因误动的可能性就更高了，因此它只适用于以下情况：允许更高越限或者作为具有超过100ms延时的延时距离保护段。线路差动保护的补充在一些线路差动保护终端设备中（如REL 561）距离保护装置能够成为一个有选择性的保护。同时它是超出反方向末端电流互感器以外故障时的主保护，这个功能由带延时段实现（如II段），它覆盖了所有相邻母线，因此形成了母线的主保护或后备保护。所以超越段应处于持续动作状态。保护范围为部分线路的保护段（如I段）可以作为线路差动保护的后备。只要差动保护动作这个功能就不需要了。为了减小I段误动的风险，可以在差动保护拒动时将其投入，差动保护失灵的最大原因就是通信系统故障。由于这个原因用于距离保护的通信方案应该使用另一个通信途径而舍弃用于线路差动保护的那一个方案。简单参数的整定每一距离保护段基本上包含了作为相对地、相间测量的完全独立的整定参数。这是复杂网络结构中和那些被要求使新配置的距离保护装置适应目前其他类型继电器的网络的一个优势情况。一套简明的可选择参数适用于反映各种类型故障的相同最大保护范围是一个标准惯例的场合。参看整定参数和整定操作说明表格。基本特性作为合成到线路REX 5XX保护终端的距离保护装置是一个全方案的距离保护。这意味着在不同范围内对于各种类型故障它都有单独的测量元件。根据终端类型，它至少由5个独立的阻抗测量范围（详情参看通信规则详文）组成，每一个都是四边形特性，示例插图如图38。RL和XL代表线路电阻和电抗，RF代表保护范围的电阻最大值。A1.2 Line impedanceAbout this chapterThis chapter describes the line impedance functions in the terminal.1 Distance protection (ZM1-5)1.1 ApplicationGeneralThe distance protection function is the most widely spread protection function in transmission and subtransmission networks. It is also becoming increasingly important indistribution networks. The main reasons for this are:• Its independence on communication links between the line ends, because for its operation,it uses information about the locally available currents and voltages.• The distance protection forms a relatively selective protection system (non-unit protectionsystem) in the power network. This means that it can also operate as a remoteback-up protection for other primary elements in the network.The basic requirements for modern line protection, such as speed, sensitivity and selectivity, with their strict requirements for dependability and security (availability), aregetting more stringent. In addition, modern distance protections must be able to operate in networks with existing distance relays, which are mostly designed in a different technology (static or even electromechanical relays).Older distance relays protect in many cases power lines only at phase-to-phase and three-phase faults. Some other protection is used for phase-to-earth faults.The flexibility of modern distance protection is for this reason very important. This especially applies when it is used in a complex network configuration, for example, on parallel operating multicircuit lines and on multiterminal lines.The selective operation of the distance protection does not depend on communication facilities between two line ends. At the same time, the distance protection can detect faults beyond the current transformers at the remote terminal. This functionality makes it an ideal complement to the line differential protection function that cannot detect faults beyond the current transformer at the opposite terminal.Distance protection zonesThe distance protection function in REx 5xx line protection, control, and monitoring terminals consists of three to five independent distance protection zones, each of them comprising three measuring elements for phase-to-earth (Ph-E) faults and/or three measuring elements for phase-to-phase (Ph-PH) faults. Different terminals suit different requirements in different networks on various voltage levels. For this reason, some characteristic parameters of the distance protection function differ from terminal to terminal. For detailed information, please refer to ordering particulars for each line protection terminal REx 5xx separately.Distance protection zone five differs from other zones with respect to its speed of operation. It starts faster than other distance protection zones and might have for this reason higher overreaching for different system transients. It is for this reason suggested to use it only for the applications, which permit higher overreaching, (i.e. switch-onto-fault function) or as a time delayed distance protection zone with time delay longer than 100 ms.Complement to the line differential protectionThe distance protection function can become optional protection in some line differential protection terminals (REL 561, for example). At the same time it represents the primary protection for faults beyond the current transformers at the opposite terminal. This functionality is achieved by the time delayed overreaching zone (generally zone 2), which covers at least the adjacent busbar and thus forms a primary or back-up protectionfor the busbar. So the overreaching zone should be continuously in operation.An underreaching zone (generally zone 1) can form a back-up to the line differential protection. There is no need for this function as long as the differential protection is in operation. To minimize the risk of unwanted operation from zone 1, this function can be activated only when the differential function is out of operation. The most likelycause to lose the differential protection is a failure within the communication system.The communication scheme used with the distance protection should for this reason use another communication channel than the one used by the line differential protection.Set of simplified setting parametersEach distance protection zone comprises basically completely independent setting parameters for phase-to-earth, and for phase-to-phase measurement. This is an application advantage in complex network configurations and in networks, where it is required to adjust the newly applied distance protection functions to the existing other types of relays (overcurrent earth fault, for example).A set of simplified optional parameters is available optionally for applications, where equal zone reaches for all kinds of faults are a standard practice. See the table of setting parameters and the setting instructions.Line impedanceBasic characteristicsThe distance protection function, as built into the REx 5xx line protection terminals, is a full-scheme distance protection. This means that it has individual measuring elements for different types of faults within different zones.Depending on the type of terminal, it consists of up to five (for details see the corresponding ordering details) independent, impedance-measuring zones, each has a quadrilateral characteristic, as symbolically illustrated in figure 38. RL and XL represent line resistance and reactance and RF represents the resistive reach of a protective zone.