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1、适合农村电网的一种基于嵌入式新型无功补偿装置林宗裕，闫国琦*，郭俊波，胡泽伟，林爱栅，罗素萍（华南农业大学工程学院，广州，510642）摘要：阐述了一种以单片机为控制芯片的嵌入式新型无功补偿装置，该装置的工作原理是通过电压电流相位差的比较，获得系统的功率因数，经过嵌入式系统对数据的分析与处理，判定是否需要进行无功补偿，决策投切无功补偿设备，系统所使用的无功补偿装置是通过交直交整流逆变电路改变电压激励形式，使同性负载之间相互无功补偿，达到容性无功补偿效果。具有推广应用的价值。关键词：嵌入式系统；无功补偿；电感；功率因数；电力系统；农村电网中图分类号：TM714.3；TP 368.1 文献标识码：
2、A 文章编号Based on embedded system new reactive compensation device in the rural power grid applicationYan Guoqi，Lin Zongyu，Guo Junbo，Hu Zewei，Lin Aishan，Luo Suping，Song Zhengxu ，Yan Guoqi*（South China agricultural university engineering institute，GuangZhou，510642）Abstract: This article expounds a with
3、the single chip processor as the main control chip embedded new reactive compensation devices, The devices working principle is through the comparison of the voltage phase difference, Get the power factor system, After the embedded system analysis of the data and processing, Decided whether or not t
4、o make the reactive power compensation, The decision to cut shots of reactive power compensation equipment, System used by reactive compensation device is through the pay-straight-/ rectifier voltage inverter circuit change incentive form, make same-sex load each other between the reactive power com
5、pensation, achieve capacitive reactive compensation effect. Has the application value.Key words: Embedded system ；reactive power compensation； inductance； power factor ；power system； rural power grid1 引言电网中的无功功率的主要作用是在电路内建立电场和磁场，并用来在电气设备中建立和维持磁场，实现电磁能量的相互转换，不对外做功，只是为电力系统提供电压支持，在电源和负载之间提供电压降落所需要的势能。虽
6、然无功功率不会消耗系统的能量，但在实现无功功率的交换过程中，将引起发电和输变电及负荷上的电压升降和电能损耗。如果系统中无功功率不能保持平衡，就会使系统电压降落，降低发电，输电设备的利用率，增加线路的损耗。严重时会导致设备损害，电力系统解列，造成电压崩溃，大面积停电。无功补偿对于维持电网的无功平衡，电网的稳定运行具有积极意义。在农村电网中，由于用电设备的增加，电力系统的武功缺额比较严重，再加上农村电网中电动机的季节性投入使用，配电线路的供电半径大，轻载和空载现象比较严重，所占用的无功功率比例比较大。因此，设计一种针对农村电网的无功补偿装置对解决农村电网的无功缺额具有现实意义。通讯作者：闫国琦，男
7、，1978年6月，河北邯郸人，华南农业大学讲师，博士研究生，从事电力电子技术研究。 林宗裕，男，1988年9月，广东汕头人，华南农业大学本科，本科生，电气工程及其自动化专业。作者联系电话：13560120534E-mail：通讯地址：广州市天河区五山华南农业大学工程学院 5106422 新型无功补偿装置工作原理图1 单相电路原理图电路原理图如图1所示，通过PWM波的输出控制可以实现对整流换流桥和逆变换流桥的控制，使得补偿电感的激励电压与系统电压基频相位相差90，从而使补偿电感与系统感性负载在同一时间系中能量变化产生了相位差。这样一来，当系统感性负载吸收能量时补偿电感释放能量而补偿电感吸收能量时
8、系统感性负载释放能量，可见，系统的补偿电感相对系统呈纯容特性。在整流逆变桥中每个桥壁的IGBT触发脉冲相互成反相关系，频率为50Hz，占空比为50%，逆变桥的导通滞后整流桥1/4个工频周期时，补偿电感元件对系统而言呈纯容性，即当系统负载吸收线路能量转化磁场能时，补偿电感释放磁场能转化为线路电能。或者反之。当然，当逆变桥完全复制系统电压波形时，系统负载与补偿负载处于同一电压激励，补偿负载相当于并联在系统上。可实现对系统容性无功补偿。具体工作原理见文献1。3 硬件设计3.1 硬件总体设计电压信号电压电流互感器电流信号隔离/int0 /int1C8051 脉冲触发器电力电子开关功率显示图2 系统硬件
9、框图 本文采用C8051单片机作为控制芯片，通过电压电流互感器获得电压电流信号后，经过过零比较器进行电压放大之后再通过单稳态触发器获得电压电流过零后的相位差，通过相关计算即可获得电压电流相位差。单片机输出PWM控制信号，输出触发脉冲来驱动电力电子元件（IGBT,GTO等可关断晶闸管），使电感无功补偿设备投入运行。3.2 功率因数的获取如图4所示，通过电压电路互感器获得电压电流低压信号，再经过过零比较器可以获得电压电流波形波形过零时刻的信号，再经过单稳态触发器进行整形，获得符合单片机要求的脉冲信号，接入单片机外部中断0和外部中断1以及定时器1的计时，获得电力系统的的相位差。假设电压的相位差为，此
10、时测得的时间差为x，那么，有2/0.02=/x，进而求的此时的相位差即可顺利求的时间差。如要求电压电流相位差为90，那么此时的时间差为5ms。在这种设计中我们运用的是等效替换的概念。我们知道，功率因数表示的是有功功率和视在功率的比值，同时，他也表征电压电流的相位差，那么，我们通过电压电流过零时刻的时间差可以获得电压电流的相位差进而可以得到功率因数。图3 电压电流时间差获取电路3.3 SPWM波形产生与门极驱动模块由C8051单片机控制输出SPWM来控制IGBT整流逆变电路的触发角，使同一桥内的上下桥触发脉冲互成反相关系，左右桥相位差相差（根据系统无功补偿的需要调整逆变桥的滞后角）经过门极驱动模
11、块驱动（图4），门极驱动模块采用的是IR21系列高压驱动器，C8051单片机输出SPWM波后经过门极驱动模块控制IGBT导通。补偿电感投入使用，实现系统无功补偿。图4 SPWM波驱动原理图4 软件设计4.1 系统流程设计使用到单片机的功能只是两个外部中断和一个定时器，故此，使用内部存储器足够满足要求。程序设计部分主要有：中断信号检测处理，函数运算，显示以及判断控制等部分。初始化开始处理程序采集电压电流信号计算功率因数中断子程序投切子程序显示功率因数图5 程序设计流程框图如上图5所示，单片机接收到电压电流信号之后，进行相应程序处理后，判定是否需要进行无功补偿，若是需要则进行设备的投切，并将计算所
12、得功率因数，通过LED数码管显示。4.2 中断子程序流程图进入中断子程序0，启定时器1，开始计时，当单片机接收到电流信号时，进入中断子程序1，关闭定时器1，读取定时器的数据，通过计算可以得到电压电流相位差（即功率因数）。通过与给定相比较可以判定是否需要执行投切子程序。设定的是大于0.95的要切除容性负载，小于0.9的要投入容性负载（功率因数）。中断子程序0中断子程序1开启定时器0开始计时关闭中断，关闭定时器，读取定时器时间功率因数是否偏小？切除补偿设备投入补偿设备否是计算功率因数，显示，延时，开中断返回主函数功率因数是否偏大？是否图6 中断子程序流程5 新型无功补偿装置在农网中的应用由于农村电
13、网属于用电终端网，加上农村环境的制约，在设备的运行维护方面存在不足。采用投切电容器进行无功补偿存在以下问题：电容器的老化，电容器的充放电，电容容量不足。而采用电感补电感方式进行无功补偿则更符合农村电网的实际用电要求。根据电力电子开关制作的新型无功补偿装置具有“电感补电感”的特色，通过控制IGBT(GTO)的触发角，可以改变等效电抗的大小，为系统提供调节范围大的基波无功电流，可以改善农村电网由于用电季节性变化大带来的不利影响。新型无功补偿设备采用了电感作为补偿器件，比起电容器具有可靠性高，容量大，补偿范围广（可补偿系统容性无功，也可补偿系统感性无功），不存在放电问题。6 仿真验证图7 IGBT导
14、通角控制策略上图所示为单片机产生PWM波电路，波形图中，分别对应控制U12（U13），U11（U14），U23（U22），U21（U24）。其中整流逆变桥控制策略为上下桥之间的波形反相。逆变整流桥的控制策略滞后整流桥90。通过PWM波控制策略改变IGBT的导通状态，从而改变补偿负载的电压激励，系统无功得到补偿。采用PWM波演示是为了分析方便，在实际调试电路中应以SPWM波来控制IGBT导通角开关性能补偿效果比较理想。经过图7中PWM波控制策略，投入补偿电感后，系统负载的电压电流波形如图8，补偿电感电压电流波形如图9所示。图8 系统负载电压电流波形图9 补偿电感电压电流波形图 仿真结果表明，通过
15、整流逆变桥，改变了补偿电感两端的电压激励，与电源激励存在相位差，达到了电感补电感的作用。7 结束语针对农村电网的特点，设计的基于嵌入式的新型无功补偿装置，从应用的角度来看，实现了设计的目的，改善了农村电网无功需求的问题，具有一定的现实意义。但同时也存在着一些不足，如控制器这一块，DSP在数据处理方面的性能优于C8051单片机，这是我们研究改进的一个方向。总的来说，本文所述装置可实现投切电容实现无功补偿的功能，还比投切电容进行无功补偿具有更大的调节范围，有效避免给系统带来较大幅值电流冲击及提高系统的稳定性，有利于提高无功补偿电压和容量等级，明显降低了投资成本，提高了空间使用率。参考文献：1闫国琦
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21、struction of reactive power compensation technical solutions and the configuration of the discussion J. Water conservancy and hydropower in guangxi,power technology.2005 (2):75-77.Editors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, c
22、overing severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear the faint beeps of the worlds first satellite - Sputnik. I also missed watching Neil A
23、rmstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space race has renewed my childh
24、ood dreams to reach for the stars.As a meteorologist, Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxious for the next one: a space capsule hanging from a crane in the New Mexico desert.Its
25、 like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of th
26、e Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straight line we would be go for launch.I feel this mission was created for me because I am also a journalist and a photographer, b
27、ut above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will never reach. However, it did not stop me from feeling his pain when a gust of swirling wind
28、 kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you c
29、ould see the wrinkles of disappointment on the face of the current record holder and capcom (capsule communications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunday.The
30、weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where
31、 our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause), he c
32、an expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, Fearless Felix will unclip. He will roll back the door.Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the E
33、arth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jum
34、ps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control
35、, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to
36、 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher t
37、han 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.