1、 蚌埠學院畢業(yè)論文（設(shè)計）外 文 翻 譯題 目: 鍋爐自動給水系統(tǒng)設(shè)計 姓 名: 學 號: 系 別: 機械與電子工程系 專 業(yè): 電子信息工程 年 級: 2009級 指導老師: 高偉霞 2012年12月10日附件1：外文資料翻譯譯文PLC在蒸汽鍋爐汽包液位PID控制系統(tǒng)的應(yīng)用分析1 引言 工業(yè)蒸汽鍋爐汽包水位控制的任務(wù)是控制給水流量使其與蒸發(fā)量保持動態(tài)平衡，維持汽包水位在工藝允許的范圍內(nèi)，是保證鍋爐安全生產(chǎn)運行的必要條件，也是鍋爐正常生產(chǎn)運行的主要指標之一。若水位過高,影響汽水分離的效果,使用氣設(shè)備發(fā)生故障;而水位過低則會破壞汽水循環(huán),嚴重時導致鍋爐爆炸，所以鍋爐汽包水位必須嚴加控制。為了確保

2、鍋爐生產(chǎn)的穩(wěn)定、可靠和經(jīng)濟運行，我們設(shè)計采用了性能先進的永宏FBs-PLC、變頻調(diào)速器、計算機應(yīng)用等自動化設(shè)備組成的鍋爐PID自動控制系統(tǒng)。該控制系統(tǒng)通過檢測水汽壓力、溫度，汽包液位等運行物理量，在運行過程中全自動調(diào)節(jié)，保證了工業(yè)鍋爐的安全穩(wěn)定高效運行。2 工業(yè)鍋爐相關(guān)工藝介紹 蒸汽鍋爐是廠礦重要的動力設(shè)備，其任務(wù)是供給合格穩(wěn)定的蒸汽，以滿足負荷的需要。為此，鍋爐生產(chǎn)過程的各個主要參數(shù)都必須嚴格控制。而利用余熱氣體作為熱交換介質(zhì)的余熱鍋爐在全國占有很大的比例，其節(jié)能降耗效果尤為明顯。某化工廠硫酸余熱鍋爐就是利用沸騰爐出來的爐氣(主要是SO2)溫度過高，將其作為熱交換對象，通過余熱鍋爐副產(chǎn)中壓蒸

3、汽供各生產(chǎn)分廠使用，既保證了生產(chǎn)需要，也達到了節(jié)能降耗的目的。鍋爐是一個較為復雜的調(diào)節(jié)對象，為保證提供合格的蒸汽以適應(yīng)負荷的需要，與其配套設(shè)計的控制系統(tǒng)必須滿足各主要工藝參數(shù)的需要。余熱鍋爐工藝流程如圖1所示。圖1 余熱鍋爐工藝流程圖3 控制難點分析 鍋爐計算機控制是近年來開發(fā)的一項新技術(shù)。它是微型計算機軟、硬件、自動控制、鍋爐節(jié)能等幾項技術(shù)緊密結(jié)合的產(chǎn)物，作為鍋爐控制裝置，其主要任務(wù)是保證鍋爐的安全、穩(wěn)定、經(jīng)濟運行，減輕操作人員的勞動強度。采用微計算機控制，能對鍋爐進行過程的自動檢測、自動控制等多項功能。它的被調(diào)量是汽包水位，而調(diào)節(jié)量則是給水流量，通過對給水流量的調(diào)節(jié)，使汽包內(nèi)部的物料達到動

4、態(tài)平衡，變化在允許范圍之內(nèi)，雖然鍋爐汽包水位對蒸氣流量和給水流量變化的響應(yīng)呈積極特性，但是在負荷(蒸氣流量)急劇增加時，表現(xiàn)卻類似逆響應(yīng)特性，即所謂的虛假水位。造成這一原因是由于負荷增加時，導致汽包壓力下降，使汽包內(nèi)水的沸點溫度下降，水的沸騰突然加劇，形成大量汽泡，而使水位抬高。汽包水位控制系統(tǒng)，實質(zhì)上是維持鍋爐進出水量平衡的系統(tǒng)。它是以水位作為水量平衡與否的控制指標，通過調(diào)整進水量的多少來達到進出平衡，將汽包水位維持在汽水分離界面最大的汽包中位線附近，以提高鍋爐的蒸發(fā)效率，保證生產(chǎn)安全。由于鍋爐水位系統(tǒng)是一個設(shè)有自平衡能力的被控對象，運行中存在虛假水位現(xiàn)象，實際應(yīng)用中可根據(jù)情況采用水位單沖量

5、、水位蒸汽量雙沖量和水位、蒸汽量、給水量三沖量的控制系統(tǒng)。所謂三沖量調(diào)節(jié)系統(tǒng)就是把給水流量W，汽包水位H，蒸汽流量D三個變量通過運算后調(diào)節(jié)給水閥的調(diào)節(jié)系統(tǒng)。具體調(diào)節(jié)過程方框圖如圖2所示。圖2 三沖量調(diào)節(jié)方框圖先通過蒸汽流量變送器和給水流量變送器取得各自的信號乘以相應(yīng)的比例系數(shù)，通過比例系數(shù)可以調(diào)節(jié)蒸汽流量或給水流量對調(diào)節(jié)系統(tǒng)的影響力度。通過差壓變送器取得水位信號作為主調(diào)節(jié)信號H。如果水位設(shè)定值為G，那么在平衡條件下應(yīng)有DDk-WWk+H-G=0的關(guān)系式存在。其中Dk為蒸汽流量系數(shù) Wk為給水流量系數(shù)。如果再設(shè)定時，保證在穩(wěn)態(tài)下DDk=WWk那么就可以得到H=G。此時調(diào)節(jié)器的輸出就與符合對應(yīng)，給

6、水閥停在某一位置上。若有一個或多個信號發(fā)生變化，平衡狀態(tài)被破壞，PI調(diào)節(jié)模塊的輸出必將發(fā)生變化。當水位升高了，則調(diào)節(jié)模塊的輸出信號就減小，使得給水調(diào)節(jié)閥關(guān)小。反之，當水位降低時，調(diào)節(jié)模塊的輸出值增大，使給水閥開大。實踐證明三沖量給水單極自動調(diào)節(jié)系統(tǒng)能保持水位穩(wěn)定，且給水調(diào)節(jié)閥動作平穩(wěn)。鍋爐給水系統(tǒng)中還有一個比較重要的控制回路是給水壓力回路，因為汽包內(nèi)壓力較高，要給鍋爐補水必須提供更高的壓力，給水壓力回路的作用是提高水壓，使水能夠正常注入汽包。但在蒸汽流量未達到滿負荷時，對給水流量的要求也不高。在老式的鍋爐系統(tǒng)中一般采用給水泵一直以工頻方式運轉(zhuǎn)，用回流閥降低水壓防止爆管，現(xiàn)在一般采用通過變頻器恒

7、壓供水的方式控制水壓。鍋爐給水量通過汽包液位調(diào)節(jié)。汽包液位測量選用浮筒液位計。為有效利用轉(zhuǎn)換廢熱，降低消耗，減低勞動強度，有利于整體工藝穩(wěn)定，要求汽包液位自動控制，正常生產(chǎn)時波動應(yīng)小于5。PID調(diào)節(jié)蒸汽出口閥可以很好的控制汽包壓力。開車正常后波動范圍不大，可以不考慮。轉(zhuǎn)化負荷波動、出預熱器鍋爐給水溫度變化、鍋爐負荷波動、排污量變化這幾個因素對汽包液位的影響必須考慮。以汽包液位為主調(diào)參數(shù)、以給水流量為副調(diào)參數(shù)、以蒸汽流量為前饋，但調(diào)節(jié)效果很差。引起汽包液位的大起大落。考慮到該廢熱鍋爐控制參數(shù)耦合小，流程簡單，產(chǎn)汽量也較穩(wěn)定，我們從操作人員的操作中得到啟發(fā)，認為減少給水量的波動從而穩(wěn)定給水溫度成為

8、該廢熱鍋爐液位控制的要點。因此我們選用“以汽定水液位前饋”比值控制方案，方案框圖如圖3所示。圖3 汽定水液位前饋比值控制方案框圖其中系數(shù)K為汽水損失率(給水流量與蒸汽流量的比值)，范圍為1.11.2。PID參數(shù)為P300、I0.4、D0。這組PID參數(shù)可以使閥位波動幅度不大而回路有較快的跟蹤效果。液位前饋系數(shù)與鍋爐額定負荷密切相關(guān)，一般是額定負荷越大前饋系數(shù)也越大。本項目廢熱鍋爐的額定負荷為35th。前饋系數(shù)按表一給定，見附表圖4實時液位記錄曲線投運時首先投運給水流量單回路，調(diào)節(jié)平穩(wěn)后，再切換為蒸汽流量比值控制，液位前饋同時起作用。以汽定水液位前饋比值控制方案調(diào)試投運簡單方便，投運后經(jīng)負荷擾動

9、(產(chǎn)汽量變化)、液位擾動(排污量變化)實驗，抗擾動性能良好，投運以來運行平穩(wěn)，達到工藝要求。圖4為2.5h實時液位記錄曲線，其中記錄了負荷擾動情況。液位波動范圍3。附表 前饋系數(shù)表液位范圍（%） 55流量系數(shù)（t/h）0 -0.2 -0.4 -0.6 -0.8 -1.04 永宏P(guān)LC PID控制系統(tǒng)分析4.1 帶PID控制功能的FATEK可編程控制器 PID控制及其控制器或智能PID控制器(儀表)已經(jīng)很多，產(chǎn)品已在工程實際中得到了廣泛的應(yīng)用，有各種各樣的PID控制器產(chǎn)品，作為國產(chǎn)PLC企業(yè)，永宏電機股份公司一直致力于PLC的研究開發(fā)工作，帶PID控制功能的FATEK可編程控制器(PLC)就是利

10、用其閉環(huán)控制模塊來實現(xiàn)鍋爐汽包液位的PID控制，在異常情況下，如液位偏離正常值較大時，通過PLC控制系統(tǒng)控制，可以快速恢復水位，保證鍋爐的安全穩(wěn)定運行。當水位控制和主蒸汽溫度控制發(fā)生矛盾時，可根據(jù)矛盾的主要方面進行兩者的協(xié)調(diào)控制。它包含給水流量控制回路和汽包水位控制回路兩個控制回路，實質(zhì)上是蒸汽流量前饋與水位流量串級系統(tǒng)組成的復合控制系統(tǒng)。當蒸汽流量變化時，鍋爐汽包水位控制系統(tǒng)中的給水流量控制回路可迅速改變進水量以完成粗調(diào)，然后再由汽包水位調(diào)節(jié)器完成水位的細調(diào)。4.2 汽包水位PID控制設(shè)計優(yōu)點 (1) 減少干擾對主回路的影響，可由副回路控制器予以校正。 (2) 由于副回路的存在減少了相位滯后

11、，從而改善了主回路的響應(yīng)速度。 (3) 對控制閥特性的變化具有較好的魯棒性。 (4) 副回路可以按照主回路的需求對對象實施精確控制。 實際PLC的控制程序采用主副回路進行串級控制，即主回路的輸出作為副回路的設(shè)定值，經(jīng)副回路輸出作用于被控對象。也可以不用副回路只用主回路形成單回路調(diào)解，或手動操作完成。一般常見的過程控制應(yīng)用， 開環(huán)回路控制就可以滿足大部份的應(yīng)用要求，但隨著使用時間、組件特性變化或受控負載或外界工作環(huán)境的變化，開環(huán)回路控制因為沒有真實將受控程序的實際量反饋到控制器，因此控制結(jié)果可能與實際期望的結(jié)果會有些落差，閉環(huán)回路PID過程控制是用來克服并解決上述缺點的極佳選擇。FBS-PLC提

12、供軟件數(shù)字化的PID數(shù)學表達式，對于一般反應(yīng)的閉環(huán)回路過程控制就可應(yīng)付，但對于工業(yè)鍋爐這樣的需要有快速反應(yīng)的閉環(huán)回路控制要使用本功能需要事先評估是否可行。典型的閉環(huán)回路程控示意圖如圖5示。圖5典型閉環(huán)回路程控示意圖根據(jù)應(yīng)用要求，用戶將PID 控制器設(shè)定成比例+積分+微分控制器，其控制器的數(shù)字化數(shù)學表達式如下:Mn:“n”時的控制輸出量D4005:增益常數(shù)，默認值為1000;可設(shè)定范圍為1 5000Pb:比例帶(范圍:15000，單位為0.1%; Kc(增益)=D4005/Pb) En:“n”時的誤差=設(shè)定值(SP)-“n”時的過程變數(shù)值(PVn) Ki:積分常數(shù)( 范圍:09999，相當于0.

13、0099.99 Repeats/Minute) Td:微積分時間常數(shù)(范圍:09999，相當于0.0099.99Minute) PVn:“n”時的過程變數(shù)值PVn-1:“n”時的上一次過程變數(shù)值Ts:PID運算的間隔時間(范圍:13000，單位:0.01S) Bias:偏置輸出量(范圍:016383)加上微分項的控制器，目的在于消除程控系統(tǒng)的過度反應(yīng)，進而使程控系統(tǒng)能夠平穩(wěn)緩和達到穩(wěn)定。雖然微分項有上述優(yōu)點，但因其對輸出量的貢獻相當靈敏，大部分的應(yīng)用不必使用微分項而將Td設(shè)定為0。PID控制器的參數(shù)整定是控制系統(tǒng)設(shè)計的核心內(nèi)容。它是根據(jù)被控過程的特性確定PID控制器的比例系數(shù)、積分時間和微分時

14、間的大小。PID控制器參數(shù)整定的方法很多，概括起來有兩大類:一是理論計算整定法。它主要是依據(jù)系統(tǒng)的數(shù)學模型，經(jīng)過理論計算確定控制器參數(shù)。這種方法所得到的計算數(shù)據(jù)未必可以直接用，還必須通過工程實際進行調(diào)整和修改。二是工程整定方法，它主要依賴工程經(jīng)驗，直接在控制系統(tǒng)的試驗中進行，且方法簡單、易于掌握，在工程實際中被廣泛采用。PID控制器參數(shù)的工程整定方法，主要有臨界比例法、反應(yīng)曲線法和衰減法。三種方法各有其特點，其共同點都是通過試驗，然后按照工程經(jīng)驗公式對控制器參數(shù)進行整定。但無論采用哪一種方法所得到的控制器參數(shù)，都需要在實際運行中進行最后調(diào)整與完善。現(xiàn)在一般采用的是臨界比例法。利用該方法進行PI

15、D控制器參數(shù)的整定步驟如下: (1) 首先預選擇一個足夠短的采樣周期讓系統(tǒng)工作; (2) 僅加入比例控制環(huán)節(jié)，直到系統(tǒng)對輸入的階躍響應(yīng)出現(xiàn)臨界振蕩，記下這時的比例放大系數(shù)和臨界振蕩周期; (3) 在一定的控制度下通過公式計算得到PID控制器的參數(shù)。除此以外為保證鍋爐運行的安全，在進行自動化控制系統(tǒng)設(shè)計時，對鍋爐水位、鍋爐汽包壓力等重要參數(shù)應(yīng)設(shè)置常規(guī)儀表及報警裝置，以保證水位和汽包壓力有雙重甚至三重報警裝置，這是必不可少的，以免鍋爐發(fā)生重大事故。5 結(jié)束語 由于采用了PLC進行控制，系統(tǒng)功能完善，結(jié)構(gòu)先進合理，能耗小，擴展靈活，便于維護，并且可靠性高，而且還極大地提高了企業(yè)的生產(chǎn)效率和經(jīng)濟效益。

16、該系統(tǒng)自動化程度較高，大大降低了操作者勞動強度，降低了成本，經(jīng)過近2年的運行，用戶給予了很高評價，認為利用國產(chǎn)永宏P(guān)LC開發(fā)的控制系統(tǒng)功能完善，綜合性強，人機界面友好，實用性好。隨著國產(chǎn)優(yōu)秀可編程控制器和高速計算元件的快速發(fā)展，鍋爐控制系統(tǒng)將會更加完善。附件2：外文原文PLC in steam boiler steam drum fluid position PID control system applied analysis 1 introduction The industry steam boiler steam drum water monitor duty is the contr

17、ol causes it for the water current capacity with the transpiration rate maintenance dynamical equilibrium, maintains the steam drum water level in the craft permission scope, is guarantees the boiler safety in production movement the essential condition, also is one of boiler regular production move

18、ment major targets or quotas. If the water level excessively is high, affects the soft drink separation the effect, the use was mad the equipment breaks down; But the water level excessively low can destroy the soft drink circulation, is serious when causes the explosion of a boiler, therefore the b

19、oiler steam drum water level must strictly control. In order to guarantee the boiler to produce stable, reliable and the economical movement, we designed use the performance to be advanced the boiler PID automatic control system which forever great automatic equipment and so on FBs-PLC, frequency co

20、nversion velometer, computer application will compose. This control system through examination water vapor pressure, temperature, movement physical quantity and so on steam drum fluid position, in movement process entire automatic control, has guaranteed the industry boiler security stable highly ef

21、fective movement. 2 industries boilers related craft introduction The steam boiler is the factories and mines important power equipment, its duty is the supplies qualified stable steam, satisfies the load the need. Therefore, boiler production process each main parameter all must strictly control. B

22、ut holds the very great proportion using the afterheat gas as the heat change medium afterheat boiler in the nation, its energy conservation falls consumes the effect especially to be obvious. Some chemical plant sulfuric acid afterheat boiler is the furnace gas which comes out using the ebullition

23、stove (mainly is SO2) the hyperpyrexia, takes it as the heat change object, through afterheat boiler vice- mid-production pressure steam for each production branch factory use, also has guaranteed the production need, also had achieved the energy conservation falls the goal which consumes. The boile

24、r is a more complex controlled member, provides the qualified steam for the guarantee to meet the load need, if the necessary design control system must satisfy each main craft parameter the need. Afterheat boiler technical process like chart 1 shows:Chart 1 afterheat boiler flow chart3 controls dif

25、ficulties analysis The boiler computer control is a new technology which the recent years developed. It is the microcomputer soft, the hardware, the automatic control, the boiler energy conservation and so on several technical in close integration with product, as the boiler control device, its prim

26、ary mission is guaranteed the boiler the security, is stable, the economical movement, reduces operators labor intensity. Uses the micro computer control, can carry on the process to the boiler the automatic detection, the automatic control and so on many functions. It is adjusted the quantity is th

27、e steam drum water level, but adjusts the quantity is for the water current capacity, through to gives the water current capacity the adjustment, enables the steam drum interior the material to achieve the dynamical equilibrium, changes in the permission scope, although the boiler steam drum water l

28、evel assumes the positive characteristic to the vapor current capacity and for the fluent quantity change response, but when load (vapor current capacity) sharp growth, performance actually similar counter response characteristic, namely so-called false water level. Creates this reason is because ti

29、me load increase, causes the dome pressure to drop, causes the steam drum boiling temperature to drop, the water ebullition suddenly intensifies, forms the massive steam bubbles, but makes the water level to raise. The steam drum water monitor system, in the essence is maintains the boiler turnover

30、water volume balance the system. It is by the water level took the water volume balance or not control target, through adjusts the water volume how many to achieve the turnover balance, maintains the steam drum water level in the soft drink separation contact surface biggest steam drum nearby the po

31、sition line, enhances the boiler the vaporization efficiency, the guarantee production safety. Because the boiler water level system is equipped with the balance of the ability to control the object, in the movement has the false water level phenomenon, in the practical application may use the water

32、 level single impulse, the water level steam quantity double impulse and the water level, the steam quantity according to the situation, gives the water volume three impulses the control systems. The so-called three impulses governing system is gives water current capacity W, steam drum water level

33、H, the steam current capacity D three variables adjusts after the operation gives the water valve the governing system. Concrete adjustment process block diagram like chart 2 showsChart 2 impulse adjustment block diagram First and obtains respective signal through vapor stream quantitative change de

34、livering for fluent quantitative change delivering while by the corresponding scale-up factor, may adjust the steam current capacity through the scale-up factor or give the water current capacity to the governing system influence dynamics. Changes delivering through the difference pressure to obtain

35、 the water level signal to take host adjustment signal H. If the water level supposes the definite value is G, then should have under the equilibrium condition DDk-WWk+H-G=0 relational type existence. Dk is steam discharge coefficient Wk gives the water discharge coefficient. If again establishes ti

36、me, guaranteed DDk=WWk that may obtain H=G under the stable state. This time the regulator output on with conforms to the correspondence, stops to the water valve in some position. If has or many signals changes, the state of equilibrium is destroyed, the PI adjustment module output will certainly t

37、o change. When the water level elevated, then the adjustment module output signal reduces, causes to close slightly for the water regulating valve. Otherwise, when the water level reduces, the adjustment module output value increases, causes to open in a big way to the water valve. The practice prov

38、ed three impulses can maintain the water level for the water single pole regulator system stably, also gives the water regulating valve movement to be steady. The boiler also has a quite important control loop for the aqueous system in is for the hydraulic pressure return route, because the steam dr

39、um internal pressure is higher, must make up the water to the boiler to have to provide a higher pressure, enhances the hydraulic pressure for the hydraulic pressure return route function, enables the water normally to pour into the steam drum. But in the steam current capacity had not achieved when

40、 full load, to gives the water current capacity the request not to be high. Generally uses the feed pump in the old style boiler system continuously by the labor frequency way revolution, reduces the hydraulic pressure with the return valve to prevent the cartridge igniter, now generally uses throug

41、h the frequency changer constant pressure water supply way control hydraulic pressure. Boiler to water volume through steam drum fluid position adjustment. The steam drum fluid position survey selects floats the tube liquidometer. For the effective use transformation waste heat, reduces the consumpt

42、ion, decreases the labor intensity, is advantageous is stable to the overall craft, requests the steam drum fluid position automatic control, when regular production the undulation should be smaller than 5%. The PID adjustment steam outlet valve may the very good control dome pressure. After drives

43、normally undulates the scope not to be big, may not consider. The transformed load undulation, the pre-heater boiler for the water temperature change, the boiler load undulation, dumps pollutants the quantitative change these factors to have to consider to the steam drum fluid position influence. Ta

44、ke the steam drum fluid position as the main tuning parameter, take gives the water current capacity as the vice- accent parameter, take the steam current capacity as a forward feed, but the adjustment effect is very bad. Causes the steam drum fluid position major rises and falls. Considered this wa

45、ste heat boiler controlled variable coupling small, flow simple, produces the steam quantity to be also stabler, we are inspired from in operators operation, thinks the reduction thus to stabilize to the water volume undulation to the water temperature becomes this waste heat boiler fluid position c

46、ontrol the main point. Therefore we select to the steam decide the water + fluid position forward feed the ratio control plan, plan diagram like chart 3 shows.Chart 3 the steam decides the water + fluid position forward feed ratio control plan diagram Coefficient K is the soft drink loss factor (giv

47、es water current capacity and steam current capacity ratio), the scope is 1.1 1.2. The PID parameter is P = 300%, I = 0.4, D = 0. This group of PID parameter may enable the valve position margin of fluctuation not greatly but the return route to have the quicker track effect. The fluid position forw

48、ard feed coefficient and the boiler fixed load close correlation, generally are the fixed load bigger forward feed coefficient is also bigger. This project waste heat boiler fixed load is 35t/h. The forward feed coefficient as soon as assigns according to the table, sees the attached list:The attach

49、ed list forward feed is a mathematical tableThe scope of Level（%） 55Flowcoefficien（t/h）0 -0.2 -0.4 -0.6 -0.8 -1.0Throws transports when first throws transports for the water current capacity single return route, after the adjustment is steady, then cuts for the steam current capacity ratio control,

50、at the same time the fluid position forward feed the function. To the steam decides the water + fluid position forward feed ratio control plan to move transports simply convenient, after throws transports (produces steam quantitative change) after the load perturbation, the fluid position perturbati

51、on (dumps pollutants quantitative change) to test, since the anti- perturbation performance has been good, throws transports moves steadily, achieves the technological requirement. Chart 4 was the 2.5h real-time fluid position record curve, in which has recorded the load perturbation situation. Flui

52、d position undulation scope 3%.Chart 4 real-time fluids positions record curve4 forever great PLC PID control system analysis4.1 brings PID the control function the FATEK programmable controller PID control and its controller or intelligent PID controller (measuring appliance) already very many, the

53、 product actual center obtained the widespread application in the project, has various PID controller product, took the domestically produced PLC enterprise, forever the great electrical machinery joint-stock company continuously will devote to the PLC research development work, will bring PID the c

54、ontrol function the FATEK programmable controller (PLC) will be uses its closed-loop control module to realize the boiler steam drum fluid position PID control, in unusual situation, when the fluid position deviation normal value will be bigger, through the PLC control system control, will be allowe

55、d fast to restore the water level, will guarantee the boiler the security stable movement. When the water monitor and the host vapor temperature control has the contradiction, may act according to the contradictory principal aspect to carry on two coordination controls. It contains for the water flo

56、w control return route and the steam drum water monitor return route two control loops, in the essence is the steam current capacity forward feed and the water level - current capacity cascade system composition compound control system. When steam current capacity change, in the boiler steam drum wa

57、ter monitor system may rapidly change the water volume for the water flow control return route to complete the coarse adjustment, then completes the water level again by the steam drum water level regulator the thin accent. 4.2 steam drums waters level PID control design merit (1) reduces the disturbance to the host return route influence, may adjust by the vice- return route controller. (2) because the vice- return route existence reduced the phase lag, thus improved the