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1、发电机PLC型励磁装置的研制与应用程远楚武汉大学动力工程系摘要：关键词：发电机 PLC 励磁1引言随着电力系统的发展，对发电机的励磁系统提出了更高的要求，一方面，要求励磁系统高度可靠，另一方面，要求励磁控制器能根据系统需要提供适当的稳定控制信号。为解决系统的稳定性问题，各种新的控制理论和方法被提了出来，并进行了大量的试验研究。此外，随着计算机技术的发展和实现复杂控制规律的需要，以及随着计算机监控系统的推广及水电厂无人值班、少人值守的实施，微机型励磁装置得到了广泛的采用1。目前国内的主流产品是基于单片机或DSP的微机型励磁控制装置2。国内微机励磁调节器的硬软件均由励磁生产厂家和科研单位自行设计，
2、造成系统模式、硬件体系、软件结构、通讯规约的各不相同，功能的扩展、联网能力、产品的互换性和维护性较差。并且由于硬件为自行设计生产，产品的工艺质量和设计的完善性不能保障，不同厂家生产的微机励磁装置可靠性差异较大。而可编程序控制器（PLC）由于其按复杂工业现场长期运行的标准设计，由专业化生产厂家生产，具有先进的生产工艺流程和严格的质量保证体系，抗干扰能力强、可靠性高，在工业控制领域和电力系统顺序控制中得到了大量应用3。本文介绍有关基于PLC的发电机励磁装置的研制与应用实践。2系统方案可编程控制器主要是为顺序控制而设计的，其模入、模出速度较慢，而励磁调节器恰恰有大量的模拟量需要处理，这将影响PLC励
3、磁装置的响应速度。因此限制了PLC在励磁系统中的应用。如何利用市面上可购置的PLC通过巧妙的系统设计，配置专门的特殊接口电路，提高PLC励磁系统的响应速度及解决余弦移相和频率自动修正问题，以满足发电机励磁控制的需要是本项目研究中需要解决的问题。其系统原理框图如图1所示。图1基于PLC的发电机励磁控制装置原理框图来自发电机的电压、电流等信号经调理后送入高速AD以采集发电机及励磁系统的状态信息，而开关量输入信号直接接PLC主机。PLC控制器根据采集的发电机的状态信息，经控制计算后将控制输出送高速DA模块，将控制输出转换为模拟量送至移相触发模块，产生相应的控制触发脉冲至晶闸管整流桥，以达到调节整流输
4、出的目的。采用触摸屏作为人机界面，使状态与信号显示直观，参数设置方便可靠，信息查询灵活方便。3特殊功能模块的研制31 测频测相模块研制为解决机组频率测量及发电机有功功率与无功功率的测量，研制了适合PLC的专用测频测相模块，它将发电机的电压信号转换为方波，并由CPLD电路与平滑滤波电路一起将方波的频率转换为对应的电压信号送至高速AD模块；此外，来自发电机的定子电流信号也转换为方波，并由CPLD电路测量其与电压方波信号的相位差，经平滑滤波电路后送至高速AD模块以测量发电机的功率因数角。解决了发电机频率与功率因数角的高精度测量问题。在测得发电机功率因数角后，可计算出发电机功率因数，再与测量的发电机电
5、压信号与电流信号值进行数学计算，即可得到发电机的有功率与无功功率值。从而取消了功率变送器，简化了系统结构。32移相触发模块研制对移相触发，很多整流电源系统中采用了市面上可购置的移相触发模块。但市售的用于相控整流电源的移相触发模块，用于发电机励磁时存在两个致命的缺陷：一是该类模块采用锯齿波移相，属线性移相方式，即控制角与控制电压间为线性关系，因整流桥的输出电压与控制角间为余弦函数，从而导致整流桥的输出与控制电压间为非线性关系，整个励磁系统的放大倍数在不同的工况下不一致，空载时大，并网时小，为兼顾励磁系统的空载稳定性，整机放大倍数不能取得较大，从而影响了励磁系统的动态性能；二是该类模块是适用于工频
6、的，当频率发生变化而控制电压不变时，若频率升高或降低时，整流桥输出电压会发生变化，使励磁系统不易稳定，当频率偏离50HZ较远时，会出现触发模块工作不正常，从而导致突甩负荷时发电机过电压或电压不稳定（对水电机组，甩全负荷时频率最高值可达75Hz以上）。为此，研制了高分辨率宽频率范围专用晶闸管触发模块。移相触发模块采用专用数字芯片构成，其原理性结构框图如图2所示。图2 移相触发模块的原理性结构框图该移相触发模块分辨率高，使用频率信号范围宽，能在2580Hz频率范围内正常工作，满足了水电机组的运行要求。并采用余弦移相技术，以保证励磁系统在全工域内具有相同的放大倍数。此外具有晶闸管阳极电压自动修正和整
7、流电源频率自动校正功能。4实施效果根据图1的方案，可采用Siemens公司的高性能PLC控制器S7300进行实现。此外，为满足中小型发电机组励磁的需要，所研制模块与技术可方便地应用到低档PLC中，构成低成本PLC励磁控制器。其中，基于S7-300PLC的发电机励磁装置已在白水峪等电站投入运行，基于S7-200的发电机励磁装置在红庙等电站投入运行。2008年2月，湖北省电力试验研究院对白水峪水电厂1机MEC-PLC微机静止励磁系统进行了全面的性能（包括PSS）测试，测试项目包括自动建压、调压范围、10%阶跃、通道切换、运行方式切换、PT断线、自动灭磁、频率特性、低励限制、突甩负荷、整流桥均流测试
8、、PSS试验等共15项试验。10%阶跃扰动试验过程录波如图3所示，因采用了新型控制算法4，具有良好的动态特性，超调量9%(0.9%Un)，振荡次数0.5次，调节时间1秒。其它主要结果如下：调压精度：0.1%频率特性：0.1%HZ零起升压：超调量0% 振荡次数0次 调节时间5.32秒突甩负荷：超调量11.7% 振荡次数0.5次 调节时间1.7秒调压范围：(10%125%)Un均流系数：0.97图3PLC励磁控制器10%阶跃试验曲线此外，还进行了PSS试验，当PSS不投入时，进行1%-4%的电压阶跃试验，同时启动WFLC录波，记录有功功率的摆动幅值和次数，见图4。图4不投入PSS情况下的4%电压阶
9、跃响应试验PSS投入时，进行1%-4%的电压阶跃试验，同时启动WFLC录波，记录有功功率的摆动幅值和次数，见图5。图5投入PSS情况下的4%电压阶跃响应试验由图可以看出，当不投PSS时，有功摆动次数为34次，最大摆幅为13.3314.7(14.8413.13)，阻尼比0.1(0.075)；投入PSS后，有功摆动次数减少、振幅减小，具体参数为：摆动次数为1次，最大摆幅为13.5414.24(14.5513.47)，阻尼比0.34(0.27)；可以看出，PSS投入后，几乎将振荡过程完全抑制，大大提高了机组抑制系统低频振荡的能力。5结论采用高性能通用可编程序控制器（PLC）作为硬件平台，研制了基于高
10、可靠性的可编程逻辑控制器（PLC）的发电机励磁控制器，并解决了测频测相与移相触发等PLC励磁控制器中的关键技术问题；同时将新型控制策略用于发电机的励磁控制，取得了较好的应用效果，受到了用户的欢迎和好评。发电机PLC励磁控制装置，基于标准的模件，可提高国产励磁产品质量，减少故障率，将减少电站的故障停机小时数，提高电力系统的安全运行水平，同时，可减少了调试与售后维护工作量，减少了售后维护成本，电厂的经济效益及社会效益明显。参考文献：1 熊杰，高雄清，曹照秀. 微机励磁的现状及发展趋势. 中国农村水利水电，2004，（8）：97-98.2 容太平，区干生. 基于DSP的微机励磁调节器的设计与实现.
11、华中科技大学学报(自然科学版)，2004，32（5）：19-21.3 陈旺. 可编程控制器(PLC)在水电机组自动控制中的应用. 工业控制计算机，1998，（3）：25-26.4 程远楚，漆为民，叶鲁卿，蔡维由. 发电机励磁的非线性解析模糊控制. 中国电机工程学报，2003，23（9）：121-125.联系方式：通讯地址：湖北省武汉市武昌东湖南路8号邮编：430072电话：027-62828838Editors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with C
12、NN for four years, covering 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 mi
13、ssed watching Neil Armstrong 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 h
14、as renewed my childhood 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 N
15、ew Mexico desert.Its 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 t
16、he live stream of the 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 a
17、nd a photographer, but 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 g
18、ust of swirling wind 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 skydiverWi
19、th each twist, you could 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
20、early as Sunday.The 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 (th
21、e troposphere) where 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 t
22、he tropopause), he can 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 p
23、latform.Below, the Earth 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
24、 big jumpWhen he jumps, 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
25、spins out of control, 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
26、will have to slow to 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 guarant
27、eed to work higher than 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.
