【正文】 降低功率因數(shù)（主要是頻率較低的諧波電流）以外，還將以各種方式把自己的能量傳播出去，形成對(duì)其他設(shè)備的干擾信號(hào)，嚴(yán)重的甚至使某些設(shè)備無(wú)法正 常工作。 22 變頻器干擾其他設(shè)備的根本原因，是因?yàn)槠漭斎牒洼敵鲭娏髦芯哂懈叽沃C波成分。變頻器的輸入電流中具有很大的高次諧波成分，這些高次諧波電流除了影響功率因數(shù)外，也可能對(duì)其他設(shè)備形成干擾。由于絕大多數(shù)逆變橋都采用 SPWM調(diào)制方式，其輸出電壓為占空比按正弦規(guī)律分布的系列矩形波。又由于電動(dòng)機(jī)定子繞組的電感性質(zhì)，其定子電流十分接近正弦波，但其中與載波頻率相等的諧波分量仍較大。 ５ .１變頻器的抗干擾措施 針對(duì)干擾的不同傳播方式，可采用各種相應(yīng)的抗干擾措施，主要有以下方法。 1. 變頻器側(cè) (1)對(duì)于通過(guò)感應(yīng)耦合方式傳播的干 擾，主要通過(guò)正確的布線和采用屏蔽線來(lái)削弱。 (2)對(duì)于通過(guò)電路傳導(dǎo)的干擾，主要通過(guò)增大線路在干擾頻率下的阻抗來(lái)削弱。實(shí)際上，可以串入一個(gè)小電感，它在基波頻率下的阻抗是微不足道的，但對(duì)于頻率很高的諧波電流，卻呈現(xiàn)出較高的阻抗，起到了有效的抑制作用。 (3)對(duì)于通過(guò)空中輻射方式傳播的干擾，主要通過(guò)吸收的方法來(lái)削弱。 變頻器的輸出側(cè)除了和和受控電動(dòng)機(jī)相接外，與其他設(shè)備之間極少有線路上的聯(lián)系，因此通過(guò)線路傳播其干擾的情形可不予考慮。 在變頻器的輸出側(cè)和電動(dòng)機(jī)之間串入濾波電抗器 LD，可以濾除輸出電流中的諧波成分。這樣既可以抗干擾，還減小了電動(dòng)機(jī)的諧波電流引起的附加轉(zhuǎn)矩，改善了電動(dòng)機(jī)的運(yùn)行特性。 2. 儀器側(cè) (1)電源隔離法：因?yàn)樽冾l器輸入側(cè)的諧波電流常常從電源側(cè)進(jìn)入各種儀器， 故在受干擾儀器的電源側(cè)采用有效的隔離和濾波措施。 (2)信號(hào)隔離法：在某些傳感器傳輸線較長(zhǎng)，并采用電流信號(hào)的場(chǎng)合，還可 以考慮在信號(hào)側(cè)用光耦合器進(jìn)行隔離。 因?yàn)樽冾l器在運(yùn)行中會(huì)產(chǎn)生比較大的電磁干擾，為保證 PLC 不因變頻器主電路斷路器以及開(kāi)關(guān)器件等產(chǎn)生的干擾而出現(xiàn)故障，連接時(shí)還應(yīng)注意以下問(wèn)題 : （ 1）對(duì) PLC 及變頻器本身應(yīng)按規(guī)定的接線標(biāo) 準(zhǔn)和接地條件進(jìn)行良好的接地，且在接地時(shí)應(yīng)將兩者很好地分開(kāi)。 （ 2）當(dāng)電源條件不是很好時(shí)，應(yīng)在 PLC 的電源模塊以及以 O模塊的電源線路中接人嗓音濾波器，若有必要，在變頻器的一側(cè)也應(yīng)如此 (主要是電抗器 )。 （ 3）當(dāng)兩者需要安裝于同一面配電柜中時(shí)，應(yīng)盡量將負(fù)載和控制線路分開(kāi)。 （ 4）可以通過(guò)使用屏蔽線和雙紋線來(lái)提高整個(gè)系統(tǒng)的抗干擾水平。 23 6 結(jié)束語(yǔ) 本文通過(guò) PLC 和變頻器來(lái)控制鼓風(fēng)機(jī)的變頻調(diào)速，經(jīng)過(guò)調(diào)試和運(yùn)行，基本完成了所需要的控制要求，其中變頻調(diào)速有非常重要的作用，它不僅節(jié)能還有很多其他的優(yōu)點(diǎn)。所以推廣應(yīng)用變頻調(diào) 速控制技術(shù)，對(duì)提高經(jīng)濟(jì)效益，節(jié)約能源有非常重要的作用。 PLC 對(duì)整個(gè)系統(tǒng)的控制簡(jiǎn)單方便，與單片機(jī)和傳統(tǒng)的繼電器控制相比 提高了系統(tǒng)控制的準(zhǔn)確性和可靠性。 致謝 首先 ，我要感謝王老師在這幾個(gè)月的悉心指導(dǎo)，在這次畢業(yè)設(shè)計(jì)中，她給了我很大的幫助，給我提了很多寶貴的指導(dǎo)意見(jiàn) ，幫助我完成了這次畢業(yè)設(shè)計(jì)。然后，我還要感謝我的同學(xué)，在日常的生活和學(xué)習(xí)中給予我?guī)椭?。最后，我再次由衷地感謝他們。 24 參考文獻(xiàn) [1] 韓安榮 .通用變頻器及其應(yīng)用 .機(jī)械工業(yè)出版社 [2] 黃運(yùn)生 ,陳學(xué) .鼓風(fēng)機(jī)變頻調(diào)速系統(tǒng) 的節(jié)能分析 .中南工業(yè)大學(xué)學(xué)報(bào) ,1997 4月 28(2) [3] 尚緒永 ,吳兆坤 .水煤氣爐鼓風(fēng)機(jī)的變頻調(diào)速 .煤氣與熱力 ,2020 7 [4] 宮浩然 .基于 PLC控制的變頻調(diào)速在物料攪拌系統(tǒng)中的應(yīng)用 ,武漢理工大學(xué) [5] 翟廣勝 .變頻器選擇方法及應(yīng)用 .設(shè)備管理與維修 ,2020 1 [6] 朱正中 ,胡亞非 .風(fēng)機(jī)變頻調(diào)速應(yīng)用綜述 .煤礦機(jī)械 ,2020(7) [7] 張燕賓 .變頻器的選型與安裝 .電氣時(shí)代 ,2020(1) [8] 曲海波 ,譚業(yè)軍 .通用型變頻器的接線注意事項(xiàng) .機(jī)床電器 ,2020(2) [9] 郜振國(guó) .變 頻器與 PLC連接需注意的問(wèn)題 .電工技術(shù) ,2020(3) [10] 李芳芹 ,任建興 .變頻技術(shù)在電廠泵與風(fēng)機(jī)系統(tǒng)中應(yīng)用的節(jié)能分析 .上海電力學(xué)院學(xué)報(bào) ,2020 3月 21(1) [11] 李良仁 .變頻器調(diào)速技術(shù)與應(yīng)用 .電子工業(yè)出版社 [12] 謝東 ,章彩云 .變頻調(diào)速技術(shù)在風(fēng)機(jī)節(jié)能改造中的應(yīng)用 [13] 張大鵬 .變頻調(diào)速器在鼓風(fēng)機(jī)中的應(yīng)用 [14] 趙建周 ,楊慶祥 .變頻器及其在節(jié)能方面的應(yīng)用 [15] 朱正中 ,胡亞非 .風(fēng)機(jī)變頻調(diào)速應(yīng)用綜述 [16] 戚學(xué)鋒 .高爐鼓風(fēng)機(jī)計(jì)算機(jī)控制系統(tǒng)設(shè)計(jì)與實(shí)現(xiàn) [17] 岳偉彬 .鼓 風(fēng)機(jī)變頻調(diào)速控制分析 [18] 李國(guó)厚 .PLC原理與應(yīng)用設(shè)計(jì) [19] 沈朝陽(yáng) ,胡雪峰 .鍋爐引風(fēng)機(jī)變頻調(diào)速節(jié)能改造 [20] 楊成德 ,馮傳富 .鼓風(fēng)機(jī)變頻節(jié)能分析 [21] 楊文勝 ,張?jiān)莆?.變頻調(diào)速技術(shù)在鼓風(fēng)機(jī)中的應(yīng)用 g an employment tribunal clai Employment tribunals sort out disagreements between employers and employees. You may need to make a claim to an employment tribunal if: ? you don39。t agree with the disciplinary action your employer has taken against you ? your employer dismisses you and you think that you have been dismissed unfairly. For more information about dismissal and unfair dismissal, see Dismissal. You can make a claim to an employment tribunal, even if you haven39。t appealed against the disciplinary action your employer has taken against you. However, if you win your case, the tribunal may reduce any pensation awarded to you as a result of your failure to appeal. Remember that in most cases you must make an application to an employment tribunal within three months of the date when the event you are plaining about happened. If your application is received after this time limit, the tribunal will not usually accept i. If you are worried about how the time limits apply to you, take advice from one of the anisations listed under Further help. Employment tribunals are less formal than some other courts, but it is still a legal process and you will need to give evidence under an oath or affirmation. Most people find making a claim to an employment tribunal challenging. If you are thinking about making a claim to an employment tribunal, you should get help straight away from one of the anisations listed under Further help. 25 If you are being represented by a solicitor at the tribunal, they may ask you to sign an agreement where you pay their fee out of your pensation if you win the case. This is known as a damagesbased agreement. In England and Wales, your solicitor can39。t charge you more than 35% of your pensation if you win the case. If you are thinking about signing up for a damagesbased agreement, you should make sure you39。re clear about the terms of the agreement. It might be best to get advice from an experienced adviser, for example, at a Citizens Advice Bureau. To find your nearest CAB, including those that give advice by , click on nearest CAB. For more information about making a claim to an employment tribunal, see Employment tribunals. The (lack of) air up there Watch mCayman Islandsbased Webb, the head of Fifa39。s antiracism taskforce, is in London for the Football Association39。s 150th anniversary celebrations and will attend City39。s Premier League match at Chelsea on Sunday. I am going to be at the match tomorrow and I have asked to meet Yaya Toure, he told BBC Sport. For me it39。s about how he felt and I would like to speak to him first to find out what his experience was. Uefa has opened disciplinary proceedings against CSKA for the racist behaviour of their fans during City39。s 21 win. Michel Platini, president of European football39。s governing body, has also ordered an immediate investigation into the referee39。s actions. CSKA said they were surprised and disappointed by Toure39。s plaint. In a statement the Russ