低压无功补偿控制装置投切开关比较研究_闫东柳
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低压无功补偿控制装置投切开关比较研究_闫东柳,低压,无功,补偿,控制,装置,切开,比较,研究,闫东柳
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毕 业 设 计(论文)系 别电力工程系专业班级电气07K8 学生姓名闫东柳指导教师王飞低压无功补偿控制装置投切开关比较研究题 目 二一一年六月 Development of a New Intelligent Compound Switch in Reactive Power Compensation CHEN Huai-Zhong Zhejiang Industry Polytechnic College Shaoxing, Zhejiang Province, China E-mail: AbstractAiming at the disadvantages in the application of reactive power compensation device with electromagnetic or power electronic switches for pulling in or out the capacitor, a new intelligent compound switch is developed which is based on single-chip computer AT89C52 and applied in var compensation for low voltage capacitor. compared with contactor and TSC，This compound switch has major advantages of smaller surge current in thyristor switching on or off and no loss respectively when contactor turning on. Keywords-compound switch; reactive power; compensation; zero-voltage; CAN bus I. INTRODUCTION Traditional reactive power compensation device realizes the switching of capacitor banks through controlling AC contactors or air switches, the device has the Achilles heel that the action speed of mechanical contacts and the change speed of industrial frequency voltage and current are not matched, and inrush current must be generated due to the existence of capacitor polarity in the switching process, when the inrush current shock pace is serious, arc re-ignition may be generated to cause over-voltage or over-current, thereby breaking down electric heaters. Thyristor switching trigger circuit switching capacitors which are widely used subsequently realize the reactive power compensation to the electrified wire netting and can alleviate the contradiction to a certain extent. However, since the problem of three-phase electricity zero-crossing points does not need considering when the capacitors are switched, if the capacitors are not switched in the moment of crossing the zero point, the capacitors may be burnt in practical projects due to the problems of capacitor discharge time and residual voltage. A compound switch not only can guarantee that the capacitors are input when the voltage crosses the zero point and cut when the current crosses the zero point for realizing triggering and switching of a self-adapting thyristor, but also improves the dynamic response speed switched 1. II. ESTABLISHMENT OF MATHEMATION MODEL The selection of the inputting moment of compound switches should have none impact current in the inputting process in principle. Namely the time of conducting the thyristors must be the time when the voltage of the electrified wire netting and the voltage on two ends of the switched capacitor are equal, if the voltage which is added on the capacitor has phase step changes, an impacting current may be generated, which may bring disadvantage influence such as breaking the thyristors and the like, the thyristor switching capacitor is like a mathematical model shown in Figure 1: Figure 1. The model of thyristor controlling capacitance In the Figure 1, L is the summation of system equivalent reactance, and the model ignores resistance. Laplace transformation voltage equation is: 2010 International Conference on Electrical and Control Engineering978-0-7695-4031-3/10 $26.00 2010 IEEEDOI 10.1109/iCECE.2010.88836382010 International Conference on Electrical and Control Engineering978-0-7695-4031-3/10 $26.00 2010 IEEEDOI 10.1109/iCECE.2010.8883638 0( )(1/) ( )/U SLSCS I SUS=+ (1) The power supply voltage is set as 0sin()muUt=+, and the initial voltage on the capacitor is set as 0U, the initial current of the system equivalent reactance L is set as zero, the expression of momentary current ( )i t and instantaneous voltage u(t) on the capacitor, which is obtained through Laplace inverse transformation is: 0000( )cos()coscos(sin)sinncmncmi tAUctatnc UAUt=+ （2） 00( )sin()coscos(sin)sinncmncmu tAUtatn UAUt=+ （3） 00/1/nnLC= （4） 221cnAn= （5） In the expression, cA is LC amplification coefficient of resonant vibration, 0 is industrial frequency angular frequency, n is natural angular frequency, and mU is voltage steady state peak value. The condition for satisfying re-triggering of thyristors and not causing great inrush current is: 0sin0cmUAU= (6) When the voltage differences on two ends of thyristors are zero in the moment that the capacitor is input, the formula is changed into: 00( )cos()coscoscmni tAUctat=+ (7) Thereby, the capacitor should be input when the voltage differences on two ends of thyristors are zero, the capacitor should be input when the voltage differences of the thyristors cross the zero point and the capacitor should be cut when the current crosses the zero point in practical projects, thereby achieving better application results 2. III. COMPOSITION PRICIPLES OF SWITCH In order to realize the conduction and cutting control of the compound switch, improve the anti-interference ability thereof, and match with various different AC contactors or high power relays, the paper proposes an intelligent compound switch with a 89C52 microcomputer as the core, the general structure is shown as the Figure 2, and the intelligent compound switch is composed of a 89C52 single chip microcomputer system and circuits such as thyristor drive, contactor drive, signal direction, safety protection, control and the like. Figure 2. Hardware structure chart A. Thyristor Switching Circuit Transient-free inputting of compensation capacitors can be conveniently realized through adopting MOC3081 chips produced by Motorola Company. The single-phase control circuit is shown as the Figure 3: Figure .3. Principle of controlling circuit From the figure, it can be observed that the thyristor control circuit is composed of an optical coupler MOC3081, a thyristor T, a contactor and the like. One input end of the MOC3081 is connected with an output end of the single chip microcomputer, the other end is connected with a power supply end, a gate pole of the thyristor is connected with one output end of the optical coupler, another two ends are connected with contacts of the contactor in parallel and are switched into the compensation loop, then, two ends of thyristors are connected with one RC resistance-capacitance SCM AT89C52 Power Watch dog Detect signalControl signalDrive thyristorDrive contactorKeyboard Monitor 36393639 absorption loop in parallel. R7 is a current-limiting resistor and is used to limit the current which flows through the output end of the MOC3081 not to exceed. MOC3081 chips can automatically detect the voltage differences on two sides of a thyristor switch T, when the voltage difference is zero, trigger pulse is sent, and the compensation capacitor is input. B. Working Principle of compound Switch The realizing method is that when in inputting, the thyristor passes zero-triggering firstly in the moment that the voltage crosses zero, and the contactor is sucked and conducted after being stabilized, and when in cutting, the contactor is firstly disconnected and the thyristor delays zero-crossing disconnection, thereby realizing cutting when the current crosses zero. 3The time sequence of compound switch control signals is shown as the Figure 4. T represents enable signals of thyristor trigger pulse, R represents switch signals of AC contactors, and S represents switch signals of the compound switch. (a) Turn-on Timing (b) Turn-off Timing Figure 4. Control signal timing diagram In a single-phase compound switch, when the A-phase capacitor C needs inputting, the operation sequence of each switch is that firstly, K2 should be closed, trigger pulse is sent to the thyristor, since each industrial frequency circle only appears once when in the moment that the voltage crosses zero, the conducting time T1 of the thyristor needs 20ms as slow as possible for conducting the thyristor switch, secondly, after T1 is selected as 25ms normally, the switch K1 is closed to act signals in order to guarantee complete conduction of the thyristor switch, thirdly, in order to guarantee that the thyristor switch can be disconnected after the contact of the AC contactor is completely conducted, after the switch signal of the AC contactor is set to be 1, the enable signal of the thyristor trigger pulse can be set to be 0 after delay for certain time, and the delay time is T2 and should be bigger than the brake closing time of the AC contactor. After the thyristor is disconnected, the switch K2 needs disconnecting finally, thereby the capacitor C can be input for work, when another group of capacitors need inputting, the operation can be carried out according to the same order. When the capacitor C needs cutting, the switch order is basically the same with the above order, only the closing of the switch K1 should be changed into disconnection of switch K1 in the second step, thereby capacitor C can be cut from the system. Reactive compensation of three phases electrified netting adopts two compensation modes 4. Under the condition that three-phase load is balanced, a mode of three-phase common compensation is adopted, and the capacitor adopts a triangle connection mode. Under the condition that the load is not balanced and the difference between the power factor angle and the current of the three phases is bigger, a separate compensation mode is adopted; the capacitors adopt a star-shaped connection mode. The adoption of the triangle connection mode can lower the current capacity of thyristors, does not have voltage shift caused by neutral points, and has more application. The wiring diagram of three-phase common compensation compound switches is shown as Figure 5: Figure 5. Diagram of three-phase total complement As for the three-phase common compensation compound switch, the closing sequence of the switch is assumed as A B C, when a brake closing signal is available, K2 and K3 of B and C are disconnected, A-phase thyristor does not need to detect zero-crossing point but to apply trigger pulse to the gate pole of the A-phase thyristor, then, the voltage 36403640 zero-crossing point of K2 switch of B-phase is detected, and the B-phase thyristors are conducted when in zero-crossing. Then, the zero-crossing points on two ends of the K3 switch of the C-phase are detected, and C-phase thyristors are conducted when in zero-crossing. After the three-phase thyristors are conducted, the contactor is acted after delay of certain time. The thyristors exit from the conduction state in turn. IV. SOFTWARE DESIGN In order to receive switching instructions, intelligent compound switch is communicated with a controller through the CAN bus, after the CAN controller SJA1000 is initialized and CAN bus communication is established, the module can send and receive CAN data packs through a CAN bus, the sending of message is automatically finished by SJA1000 according to CAN rules, and a main controller must send information which needs sending into a sending buffer of SJA1000. The CAN controller SJA1000 automatically receives the message according to rules, received message is placed into a receiving buffer, the state sign RBS of the receiving buffer is set to be 1. The receiving process can be carried out through the interruption request of SJA1000 or through searching the sign of SJA1000. The single chip microcomputer generates serial port interruption and receives control words sent by the CAN controller, corresponding operation is carried out, the execution result is sent back, the data receiving and processing flow of subroutine is interrupted, and the flow chart is shown as the Figure 6: Figure 6. Data receiving and processing flow chart Since the switching delay time can be adjusted through control words sent by the controller, the device is applicable to AC contactors or high power relays with different types. V. CONCLUSION The compound switch which is introduced in the paper has the main advantages that the switch not only has the advantages that the capacitor is input when the thyristor crosses zero, but also has the advantage of none power consumption when the contactor is closed5. The switch adopts advanced zero-crossing triggering technique to solve the error triggering problem of thyristor cutting, avoids switching oscillation, does not have inrush current impact, has fast dynamic response, greatly prolongs the service life of capacitors, and has prominent energy-saving effect and has wide development prospect in the application of low voltage reactive power compensation. ACKNOWLEDGEMENTS This work is supported by high technique innovation project of Zhejiang Province Science and Technology Department (No.2008R30030) and science research project of Zhejiang Province Department of Education (No.20060053). REFERENCES 1 S.G.Luo et al, An adaptive detecting method for harmonic and reactive current, IEEE Trans on industrial Electronics, vol.42, pp. 85-89, Jannary 1995. 2 HAI Tao, XU Yan, fuzzy control; parallel capacitor switching, reactive compensation Journal of Guangxi University, vol.9, pp. 260-262, March 2005. 3 ZHANG Cuizhe, LI Wenhua Study on Intelligent Compound Switch for Reactive Power Compensation Device, Low Voltage Apparatus vol.9, pp.57-59,September 2007. 4 NAN Yurong, LI Gang, Compound Switch and Its Application in Var Compensation of Low voltage Based on Single chip Computer Modern Electronic Technique, vol.182, pp. 84-86, Augusst 2004. 5 YANG Xiaoping 1, WANG Xiaodong, Research of Reactive Power Compensation Device with Capacitor Switched by Compound Switch, Modern Electronic Technique, vol.202, pp. 103-105, September 2005. Interruption entry Interruption entry Interruption? Read receive buffer Release receive buffer Implement compound control strategies Open interruption Interruption return N Y 36413641华 北 电 力 大 学 毕 业 设 计（论 文）开 题 报 告学生姓名： 闫东柳 班级： 电气07K8 所在院系： 电力工程系 所在专业：电气工程及其自动化设计（论文）题目：低压无功补偿控制装置投切开关比较研究 指导教师： 王飞 2011年 3 月 17日毕 业 设 计（论 文）开 题 报 告一、结合毕业设计（论文）课题情况，根据所查阅的文献资料，每人撰写不低于2000字的文献综述。（另附）二、本课题要研究或解决的问题和拟采用的研究手段（途径）：1、 研究的内容在了解无功补偿装置基本工作原理和不同类型投切开关动作特点的基础上，针对主电路形式、投切开关类型进行的不同，对涌流进行研究。2、 研究手段选择接触器、晶闸管、复合开关3种不同类型投切开关，设计建立低压配电网无功综合补偿装置MATLAB/PSCAD仿真模型，进行不同类型投切开关动作过程的涌流仿真研究，分析开关类型、投切控制信号、可控硅触发方式对涌流波形、数值的影响，对不同类型投切开关的特性进行对比分析。三、指导教师意见：1 对“文献综述”的评语： 2对学生前期工作情况的评价（包括确定的研究方法、手段是否合理等方面）：指导教师： 年 月 日低压无功补偿控制装置投切开关的研究综述闫东柳摘要：首先对无功功率补偿及其重要性进行简单介绍；指出通过改变并联电容器的容量（即以投切电容器的方法）以改变无功功率的无功补偿装置，是目前被普遍采用的最经济最行之有效的方法；提出正确选用低压无功补偿电容投切装置有着十分重要的意义。然后主要综述了接触器、晶闸管和复合开关这3种投切开关的基本构成、基本原理以及各自的主要特点，同时对比分析了各种开关的利弊，并对其在低压无功补偿装置中的应用进行了系统的总结；最后强调了正确的、合理的选用投切开关对低压无功补偿的重要性。关键词：无功补偿；接触器；晶闸管；复合开关前言随着我国国民经济连续多年的高速增长，现有供电设备虽经多次改造，仍然难以满足日益增长的电力负荷需求，全国各地已不同程度地出现了缺电和拉闸限电的现象。解决电力供应紧张的问题，除了加快发电厂建设以外，采用合理的无功补偿也不失为一条有效的途径。在工业企业中，异步电动机、变压器等大量感性负载的存在必然会产生一定的无功功率，这增加了设备容量以及输电线路和变压器的损耗，从而导致用电效率低下，直接影响自动化设备的正常运行。所谓无功功率补偿，是指在电网中安装并联电容器、同步调相机等设备，向感性负荷设备提供无功功率，减少由输电线路输送的无功功率，从而减少了无功功率在电网中的流动。无功补偿的基本原理是：把具有容性功率的负荷装置与感性功率负荷并联在同一电路。当容性装置释放能量时，感性负荷吸收能量；当感性负荷释放能量时，容性装置吸收能量，能量在2种负荷之间相互交换。这样，感性负荷所需要的无功功率可由容性负荷输出的无功功率进行补偿，从而对无功功率进行调度以改善交流电力系统的供电质量，达到校正功率因数、调节电压和平衡各相负载的目的1。做好无功补偿工作，不但可起到扩大现有输变电设备供电能力、改善电能质量、降低线路损耗、缓解供电能力不足的作用，而且还能取得良好的经济效益，如延长供用电设备的使用寿命、降低用户的电费支出等。无功补偿的重要性及其解决问题的现实性，目前已得到了业内共识，各地也相继安装了许多不同形式的低压无功补偿装置，但从其使用的效果来看却不尽相同。其中通过改变并联电容器的容量（即以投切电容器的方法）以改变无功功率的无功补偿装置，是目前被普遍采用的最经济最行之有效的方法。无功补偿装置中主要元件是电容器和投切开关，投切开关的性能直接影响到电容器的使用寿命及补偿效果，所以其性能就将是至关重要了。正确选用低压无功补偿电容投切装置。对于保证低压无功补偿设备的可靠性、经济性及补偿效果有着十分重要的意义。目前在我国投入使用的低压无功补偿电容投切装置主要有以下三种：接触器。晶闸管。复合开关。本文就这三种装置的基本构成及工作原理作一分析，同时介绍各自的主要特点，以供广大设计人员选用时参考2。2 国内外研究现状2.1接触器接触器电容投切装置由接触器（主触头、辅助触头、线圈）和电阻切合电路组成，通过专用的电容补偿控制器控制该装置的开与关, 实现电容器的投入与切除。当该装置接收到来自控制器投入电容器的指令后，电阻切合电路提前接通，电流流经电阻向电容器充电，电阻抑制了电容器的合闸涌流，随后主触头闭合，承载了电容器的正常工作，同时短接电阻，完成电容器的投入过程。当该装置接收到来自控制器切除电容器的指令后，主触头先断开，电阻切合电路延时断开，抑制了电容器切断时的操作过电压，完成电容器的切除过程2。接触器投入过程中，由于电容器上可能有剩余电压,当系统电压和电容器残压的差值较大时接触器会产生很大的冲击电流,直接损坏接触器。试验表明，合闸涌流严重时可达电容器额定电流的50倍，产品按标准GB/T 22582-2008要求，装置的最后一组电容器投入运行瞬间产生的涌流应限制在电容器组额定电流的20倍以下（通常为10倍左右）3。这不仅影响电容器和接触器的使用寿命，而且对电网造成冲击，影响其它设备的正常工作。后来采用串接电抗器和加入限流电阻来抑制涌流，虽然可以控制在额定电流20倍以内，但从长期运行情况来看，其故障率仍然非常高，维修费用较高4。优点：价格低，无漏电流，由于接触器的电阻小，所以导通容量大、压降小、功耗低。缺点：涌流大，投切反应速度慢，对电网造成冲击且故障率高，影响补偿装置寿命。这种开关不能满足系统对补偿装置快速、频繁、安全可靠动作的要求。随着电力电子技术的发展,出现了无触点开关。2.2晶闸管晶闸管投切电容装置采用晶闸管双向反并联而成，通过专用电容补偿控制器和过零触发电路控制晶闸管的导通。当该装置接收到来自控制器投入电容器的指令后，在触发电路检测到施加于晶闸管两端的电压为零时，发出触发信号，晶闸管导通，此时电容器的电压与电网的电压相等，因此不存在合闸涌流，完成电容器的投入过程。当该装置接收到来自控制器切除电容器的指令后，触发电路去掉触发信号，在电流过零时，晶闸管截止，将电容器从电网中切除。整个投切过程是利用晶闸管反应速度快、无触点、过零触发的特点，实现电容器无涌流、无过电压的快速投切2。但是，晶闸管导通时会有1V左右的压降，运行中存在不可忽略的能耗和发热的问题。通常15kvar 三角形接法的电容器，额定电流为21.7A，则一相晶闸管所消耗功率约为21.7W，三相晶闸管投入时，所消耗功率约为65.1W。因此需要采取相应的散热降温措施4。此外在采用晶闸管控制投切电容器的动态无功补偿装置中, 晶闸管对驱动信号要求严格,故驱动电路相当复杂5。同时晶闸管有漏电流存在，当未接电容时，即使晶闸管未导通,其输出端也是高电压。其优点：无触点，无合闸涌流，投切反应速度快，使用寿命长，维护方便。缺点：价格高，功耗大，发热量高，散热系统复杂，有漏电流。由此可见,采用晶闸管作为电容器的投切开关, 虽然解决了电容器投切过程中的涌流、过压、分断电弧等问题, 但其自身也存在着明显不足,如散热器体积大、冷却风扇易损坏、需外加温控开关和触发电路等辅助器件、结构复杂等等6。2.3复合开关复合开关投切电容装置采用双向反并联晶闸管及交流接触器组成，装置由补偿控制器及复合开关控制电路进行控制。电容器过零投入。先由补偿控制器发出投入指令给该装置，在电容器的电压与电网的电压相等时，通过晶闸管投入电容器，能够达到无涌流投入电容器的目的。在电容器投入后，复合开关控制电路紧接着又发出指令给接触器，使接触器触点闭合，将晶闸管电路短接，此时晶闸管触发信号消失阳极电流过零，晶闸管自然关断。接触器承载着电容器的正常工作电流，同时承载电容器的正常工作。由于接触器闭合后的接触电阻远小于晶闸管电路导通时的电阻，达到了节能和延长晶闸管使用寿命的目的。电容器过零切除。补偿控制器首先发出切除指令给接触器，使接触器触点断开，此时晶闸管仍处于导通状态，暂时承载着电容器的正常工作电流，并于电流过零时截止，将电容器切除，达到电容器切除无过电压的目的2。复合开关投切装置工作原理是先由晶闸管在电压过零时投进电容器，然后再由交流接触器触点并联闭合，晶闸管退出，电容器在交流接触器触点闭合下运行。因而实现了投进无涌流运行不发热的目的。但为了降低本钱，通常选用两只小功率，低耐压晶闸管串联使用，利用晶闸管20ms内电流可过载10倍额定电流的特性，过零投进，再用接触器闭合运行。而交流接触器触点偏
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