毕业设计（论文）-电力负载的无功测控电路设计.doc

长江大学毕业论文（设计）题目名称：电力负载的无功测控电路设计 题目类型： 毕业设计 学生姓名： 院（系）： 电子信息学院 专业班级： 指导教师： 时间： 2010年4月1日至2010年5月23日 目录毕业设计任务书.i文献综述ii指导老师审查意见答辩会议记录评阅教师评语中外文摘要长江大学毕业设计(论文)任务书学院（系）电子信息学院 专业 仪器 班级 10601 学生姓名 指导教师/职称 1. 毕业设计(论文)题目：电力负载的无功测控电路设计2. 毕业设计（论文）起止时间：2010年03月01日2010年6月10日3毕业设计(论文)所需资料及原始数据（指导教师选定部分）1.基于msp430系列单片机的智能无功补偿控制器 2. 关于低压无功补偿装置的探讨 3. 配电系统无功补偿技术方案比较 4.电网功率因数的测量及无功自动补偿控制 4毕业设计(论文)应完成的主要内容了解实际电力负载的功率因数低的特性，分析由此造成的供电与用户的影响与损失。运用学过的知识，用电压，电流互感器进行发电机与电网的电压.电流.功率及相位的测量。运用单片机作比较计算并进行无功补偿（并联电容）。5毕业设计(论文)的目标及具体要求5.1.配电系统无功补偿的分析；5.2. 配电系统无功功率的实用检测电路设计；5.3.无功补偿的投切控制；5.4. 配电系统无功补偿的保护电路。6、完成毕业设计(论文)所需的条件及上机时数要求计算机图书馆的各种图书及杂志网上数据库上机150学时任务书批准日期 2010 年 03 月 01日 教研室(系)主任(签字) 任务书下达日期 2010 年 03月 11日 指导教师(签字) 龙从玉 完成任务日期 2010 年6月 10日 学生（签名） yangtze river university wen wen xian graduates of comprehensive statetitle name: reactive power load measurement and control circuit design department: electronic informationprofessional-level classes: instrument 10 601 student name: wang lin hua teach teachers: long congyu-teacher completion date :2010-5-3 reactive power load measurement and control circuit design literature review student: wang linhua, electronic information instructor: long congyu , telecommunications institute fist. introduction i wrote this article is to introduce the current status of power system and power compensation in power system problems. mainly related to the power system reactive power compensation in the area. reactive power load measurement and control circuit design literature review low-voltage reactive power compensation reactive power load is an important part of compensation. improve low-voltage compensation, not only can reduce the level of reactive power compensation on the pressure, but also improve the utilization of the user distribution transformers to improve power factor and voltage quality of the user, and can effectively reduce power losses, thus reducing electricity bills . reactive power compensation and power supply departments of user benefit. existing reactive power compensation device type a lot, but basically by the detection unit, control unit, execution units, and power component. the task detection unit is detected from the network and network power factor directly or indirectly related to the parameters, and to give as gifts this parameter signals and control unit, the control unit to be compared with the control target value. make switching decisions. implementation unit is based switching decisions by switching switch (ac contactor) control of capacitor switching, compensation to complete the task.second, the main at present, the low voltage reactive power compensation devices are static and dynamic compensation device compensation of two, the control method are: power factor control, reactive power (or reactive current) control and other control methods. static and dynamic reactive power compensation reactive power compensation. static var compensator svc means that when the reactive changes, control changes to control the capacitor according to the group switching to achieve the required reactive power compensation, the response normally greater than 5 seconds. capacitor switching is accomplished by the contactor, due to capacitor inrush current withstand capability and the discharge time, capacitor grade, contactors operating frequency, life and other factors, so there is much to be desired: ( 1) there is a level of compensation, timing, and thus compensation accuracy, the time when the load changes frequently (such as rolling, high-power electric furnace, etc.), to follow is not strong. (2) the input capacitor can be no surge. for contactor + reactor program, a larger increase in losses for capacitive touch device program, a high accident rate, but also a great influence on the life of the capacitor. (3) run noisy. (4) as part of the load control contactor coil is in the switching process, will produce sparks and high harmonics, resulting in interference, affect the compensation device reliability and service life. static reactive power compensation equipment and some use of composite switch as the closing and breaking circuit current component, which uses silicon and contacts (or high-capacity relays) in parallel, when you need input capacitor, the first by the scr conduction circuit, no inrush current into the capacitor, and then contacts (or high-capacity relays) conduction circuit, controllable silicon out of operation. removal of the action when the capacitor is the opposite order. because of the inherent characteristics of the components used, limitations, when the controller detects reactive change needs switching capacity of the capacitor must, we must delay a certain time (response time greater than 5 s) for switching. therefore, static reactive power compensation is a longer delay switching for reactive compensation. in addition, the operation was found, due to high current flows through the relay contacts regularly, and frequent switching, make contact burning, bonding occurs. relay contacts will occur shake off timely, high harmonic generation, on the controller to work greater impact. dynamic reactive power compensation (thyristor switched capacitor tsc): as the svc is kind of long-latency switching method, which is determined by its reactive change frequently and vary greatly in the case, can not meet the requirements. in modern power electronic devices and digital control technology support, with fast switching capability of dynamic reactive power compensation device can quickly. tracking compensation of reactive power changes. static and dynamic compensation equipment circuit structure is the same, but the dynamic compensation is dynamic compensation controller to control the fast-pass thyristor .broken, no surge in power capacitor switching. reactive power regulator replaced electromagnetic ac contactors to change this component, making the performance of the compensation device has been a qualitative leap to a capacitor bank switching time reduced by a few hundred milliseconds to 20,30 ms . that is, l 2 个 a cycle is complete a capacitor bank switching, so do the amount of reactive power compensation can quickly follow changes in actual demand. as the reactive power regulator is a non-contact capacitive switch long life, so that no surge capacitors impact the process of investment, no operating over-voltage, arc-free capacitor renewed removal process, the whole long life, maintenance of small and can be removed in the capacitor after the discharge to any what input voltage again. frequent switching capacitor can be divided into phase compensation. power factor control and reactive power (reactive current) control whether static var compensation, or the dynamic reactive power compensation, require a controller to complete the network parameters of the measurement, control capacitor banks switching. most of static reactive power compensation device is a contactor switch element, the controller issued a traffic signal switches to control contactors or off closing open. dynamic reactive power compensation device to thyristors as switching elements, the controller issued a trigger signal to the thyristor. reactive power compensation device has power factor control and reactive power (no reactive current) control in two ways, each of the following features: power factor control power factor control is to meet the requirements for power factor control objectives, so that the grid power factor to meet the requirements. power factor controller on the grid voltage and current sample testing, analysis and calculation of power by the current value, with the current power factor values with the switching threshold set for comparison to determine whether investment, removal of capacitors, or maintaining the status quo unchanged. suppose the power factor before compensation 0.9. when the input threshold is set to = 0.9, the controller detects the current power factor is less than 0.9, to issue instructions, input of a compensation capacitor. if the compensated power factor 0(负载呈感性) =t-t/2= =0(负载呈阻性) 0(负载呈容性) 功率因数的计算：为使cpu有能力和时间实施自诊断和二次开发，本文对cos 的运算采用查表技术c设市电工频5o hz(周期20ms)，t=10ms，则cos=c0弧节 cos*t=cos（*t/t-/2）事先离线使 按一定步长 递增，并由上式计算得tcos查询表，存人eprom。其中把t折算为地址，地址内容为cos 值。这样当采样回路测得 时，就可将其转化为地址，查表即得对应的cos 。过程论述理解关于无功功率补偿的几个概念1.1 正弦交流电中的无功功率定义正弦电流中的无功功率定义为: 习惯上认为它是由电路中的储能元件(电容或电感)引起。在交流电一个周期的一部份时间内，储能元件从电源吸收能量，另一部时间内将能量返回电源，理想的无损失储能元件在整个周期q平均功率是零。也就是说在外电路和电感或电容之间虽有能量的来回交换，但在储能元件上并没有能量的消耗。无功功率与储能元件相关联。我们可计算功率因数： 1.2 电力系统中无功功率及功率因数电力网除了要负担用电负荷的有功功率p，还要负担负荷的无功功率q。 无功功率o和视a功率s之间存在下述关系: 然而：被定义为电力网的功率囚数，其物理意义是线路的视在功率s供给有功功率的消耗所占百分数。在电力网的运行中，我们所希望的是功率因数越大越好，如能做到这一点，则电路中的视在功率将人部分用来供给有功功率，以减少无功功率的消耗。1.2.1 如何提高电力系统功率因数功率因数还可以表示成个述形式:注：u:为线电压，l为:线电流。 可见，在一定的电压和电流卜，提高cos，其输出的有功功率将增大。因此，改善功率因数是充分发挥没备潜力，提高设备的利用率的有效方法。1.2.2 补偿电容以减少线路损失电力网的电压损失可以表示为: 可看出，影响u的因数四个:线路的有功功率p、无功功率o,电阻r和电抗x。如果采用容抗为x。的电容来补偿，则电压损失为:故采用补偿电容提高功率因数后，电压损失u减小，改善了电压质量。电力系统无功补偿的原理 2. 3. 1配电网无功补偿问题的提出 在电力系统中，由于电感、电容元件的存在，不仅系统中存在着有功功率，而且存在无功功率。虽然无功功率本身不消耗能量，它的能量只是在电源及负载间进行传输交换，但是在这种能量交换的过程会引起电能的损耗。并使电网的视在功率增大，这将对系统产生以下一系列负面影响:(1) 电网总电流增加，从而会使电力系统。中的元件，如变压器、电器设备、导线等容量增大，使用户内部的起动控制设备、量测仪表等规格、尺寸增大，因而使初投资费用增大。在传送同样的用功功率情况下，总电流的增大，使设备及线路的损耗增加，使线路及变压器的电压损失增大。(2) 电网的无功容量不足，会造成负荷端的供电电压低，影响正常生产和生活用电;反之，无功容量过剩，会造成电网的运行电压过高，电压波动率过大。(3) 降低了电网的功率因数造成大量电能损耗，当功率因数由0.8下降到0.6时，电能损耗将近提高了一倍。(4) 对电力系统的发电设备来说，无功电流的增大，对发电机转子的去磁效应增加，电压降低，如过度增加励磁电流，则使转子绕组超过允许温升。为了保证转子绕组正常工作，发电机就不允许达到预定的出力。此外，原动机的效率是按照有功功率衡量的，当发电机发出的视在功率一定时，无功功率的增加，会导致原动机效率的相对降低。目前，随着电力电子技术的迅速发展，工厂大量使用大功率开关器件组成的设备对大型、冲击型负载供电，这使电能质量问题日益严重。如果，不进行无功补偿，在正常运行时，会反复地使负载的无功功率在很大的范围内波动，这不仅使电气设备得不到充分的利用，网络传输能力下降，损耗增加，甚至还会导致设备损坏、系统瘫痪。2.3.2 无功补偿向量图在工业和生活用电负载中，阻感负载占有很大的比例:异步电动机、变压器、萤光灯等都是典型的阻感负载。异步电动机和变压器所消耗的无功功率在电力系统所提供的无功功率中占有很高的比重。电力系统的电抗器和架空线等也要消耗一些无功功率;同时，各种谐波源也要消耗一定的无功功率。阻感负载可看作电阻r与电感l串联的电路，其功率因数为 无功功率测控电路总体设计思路该无功补偿器是以无功功率为判断依据。如何进行无功补偿？设定系统所需要达到的无功功率要求，通过对系统的无功功率的检测，并以此作为是否补偿无功的标准。处理所采集的数据。显示当前系统的状态参数，如何保护补偿装置？怎样处理高压和低压的电气连接所产生的干扰和抑制谐波？重点就是如何测量无功功率，如何投切电容？总的解决方法是将无功补偿分为三个组成部分，功率因数自动调节器执行机构调节对象该无功设计思路：通过互感器采集数据，经过组合电路对电压与电流的过零比较产生其相对落后时间查 差，送入单片机，进行分析，计算，判断，对执行机构进行控制无功的投入与切除。这样就可以实现对负载的无功补偿。 该无功补偿器为单相补偿。3.1 无功功率补偿原理图无功检测电容组负载为单环闭合回路，当设定参数则可以自动调节无功功率，无功检测的数据与设定值的比较结果决定电容组的投切。3.2单相无功补偿的原理3.3无功补偿的框图：电压传感器a/d转换 单片机开关投切控制电路电容组投切光隔离复合开关电流传感器功率检测电路显示eeprom 硬件电路的设计硬件电路分为三大块：采样系统，控制系统，执行系统。分别分担各自的必要功能并构成一个完整的无功补偿电路。4.1采样系统 该无功补偿器是以无功功率为判断依据而进行无功的投切。无功补偿器关键在对无功功率的采集，样无功功率因数。4.1.1 功率因数的测量4.1.1.1信号调理电路的设计信号调理电路主要完成强电信号与弱电信号之间的隔离和变换，该电路包括互感器信号转换电路、1)互感器信号转换电路选择带8位的ad转换器，其ad转换的域值电压为33 v，其最大转换时间为。因此对于选择的交流传感器，其采样精度应与选择带8位的ad转换器采样精度相匹配。另外，电压、电流传感器的功用主要在于从主电路上适当的支路或节点处对其电压或电流值进行采样，并将控制电路与主电路进行隔离。因此，传感器的选取就要考虑到主电路及控制电路的电压(或电流)等级。对于容量为100 kvar，电压等级为380 v220 v的三相静止补偿器，所需的电流参数为系统对电网的输出无功电流参数，因此，选用北京星格公司研制的精密电压传感器spt304和精密电流传感器sct260sh304是一款电压输出型精密电压传感器，其额定输人为380 v，额定输出为125 v，线性范围为0450 v，最大输人电压为570 v，精度为02(一40+75)，相移5度sct2601是一款电流输出型精密电流互感器，其额定输人为600 a，额定输出为100 ma，线性范围为0720 a，非线性度01 ，相移05。(补偿前)。使用电路如图2所示，互感器副边电路为电流电压变换电路，调节图中反馈电阻r和r的值可得到所需的电压输出(一125 v+125 v)：电容c2是400至1 000 pf的小电容，用来去耦、滤波和相位调节。2) 采集功率因数的电路将比较器输出的两路矩形波信号u1和u2经与门74ls08相与，输出波形再同u1一起送异或门74ls86，其输出波形即显示了相位差角的大小（图2-1）。然后将信号输入89c51单片机的int0口。先通过软件对寄存器ie赋值，使int0口关中断。这是因为，定时器/计数器0检测89c51的int0口，通过定时器工作方式寄存器tmod来控制定时器/计数器0的工作方式和操作模式，通过定时器控制寄存器tcon来控制它们的工作状态。由于程序需要当int0脚由低电平变为高电平时，定时器/计数器0开始计时，为了消除外部干扰，须先将int0口关中断。定时器/计数器0选择工作方式一，将定时器工作方式寄存器tmod