【正文】 隨著科技的飛速發(fā)展，鍋爐單機(jī)容量越來(lái)越大，但各種對(duì)鍋爐汽包水位 影響的不 確定因素也越來(lái)越多，本文只是在軟件上仿真了特定條件下的水位變化，提出用模糊 PID 解決汽包水。仿真圖像結(jié)果表明控制效果較傳統(tǒng)的 PID 各項(xiàng)性能指標(biāo)有一定的提高。 （ 2）模糊 PID 控制通過(guò)不斷檢測(cè) e 及 ec，根據(jù)事先確定的模糊規(guī)則，利用模糊推理的方法，通過(guò)不斷修改 PID 控制器參數(shù) ，其具體過(guò)程是一個(gè)不斷尋優(yōu)過(guò)程，利用模糊控制器輸出調(diào)整 PID 控制器的三個(gè)參數(shù)。而模糊控制不要求知道被控對(duì)象的精確數(shù)學(xué)模型，只需要操作人員長(zhǎng)期積累的實(shí)際操作經(jīng)驗(yàn)知識(shí)及操作數(shù)據(jù)，所以人們想到把 PID 控制策略引入模糊控制中，構(gòu)成 FuzzyPID 控制。 第 五 章 結(jié)論及展望 電廠鍋爐的水位調(diào)節(jié)過(guò)程需要建立精確的數(shù)學(xué)的模型，具有非線性、不穩(wěn)定性、時(shí)滯等特點(diǎn)。 （ 5）當(dāng)控制對(duì)象參數(shù)突然發(fā)生改變時(shí)，模糊 PID 控制系統(tǒng)對(duì)它的反應(yīng)明顯很小、魯棒性好、適應(yīng)力強(qiáng)，系統(tǒng)的靜態(tài)特性和動(dòng)態(tài)特性都較好，對(duì)“虛假液位”的控制可以 取得預(yù)期的控制效果。 （ 3）當(dāng)控制對(duì)象參數(shù)突然發(fā)生變化時(shí)，單純采用 PID 控制的系統(tǒng)超調(diào)量明顯變大，響應(yīng)時(shí)間變長(zhǎng)，系統(tǒng)振蕩加劇，控制效果不好。 表 44 清晰化后的 pK 的隸屬度函數(shù)賦值表 3 2 1 0 1 2 3 3 2 1 0 1 2 3 E EC U 表 45 清晰化后的 iK 的隸屬度函數(shù)賦值表 3 2 1 0 1 2 3 3 2 1 0 1 2 3 表 46 清晰化后的 dK 的隸屬度函數(shù)賦值表 3 2 1 0 1 2 3 3 2 1 0 1 2 3 E EC U E EC U 模糊 PID 控制仿真模塊如下圖所示： 圖 47 模糊 PID 控制仿真模塊 模糊控制規(guī)則語(yǔ)言如下： (e is NB)and(ec is NB)then(kp is PB)(ki is NB)(kd is PS) (e is NB)and(ec is NM)then(kp is PB)(ki is NB)(kd is NS) (e is NB)and(ec is NS)then(kp is PM)(ki is NM)(kd is NB) (e is NB)and(ec is Z)then(kp is PM)(ki is NM)(kd is NB) (e is NB)and(ec is PS)then(kp is PS)(ki is NS)(kd is NB)) (e is NB)and(ec is PM)then(kp is Z)(ki is Z)(kd is NM) (e is NB)and(ec is PB)then(kp is Z)(ki is Z)(kd is PS) (e is NM)and(ec is NB)then(kp is PB)(ki is NB)(kd is PS) (e is NM)and(ec is NM)then(kp is PB)(ki is NB)(kd is NS) (e is NM)and(ec is NS)then(kp is PM)(ki is NM)(kd is NB) (e is NM)and(ec is Z)then(kp is PS)(ki is NS)(kd is NM) (e is NM)and(ec is PS)then(kp is PS)(ki is NS)(kd is NM) (e is NM)and(ec is PM)then(kp is Z)(ki is Z)(kd is NS) (e is NM)and(ec is PB)then(kp is NS)(ki is Z)(kd is ZE) (e is NS)and(ec is NB)then(kp is PM)(ki is NB)(kd is ZE) (e is NS)and(ec is NM)then(kp is PM)(ki is NM)(kd is NS) (e is NS)and(ec is NS)then(kp is PM)(ki is NS)(kd is NM) (e is NS)and(ec is Z)then(kp is PS)(ki is NS)(kd is NM) (e is NS)and(ec is PS)then(kp is Z)(ki is Z)(kd is NS) (e is NS)and(ec is PM)then(kp is NS)(ki is PS)(kd is NS) (e is NS)and(ec is PB)then(kp is NS)(ki is PS)(kd is ZE) (e is ZE)and(ec is NB)then(kp is PM)(ki is NM)(kd is ZE) (e is ZE)and(ec is NM)then(kp is PM)(ki is NM)(kd is NS) (e is ZE)and(ec is NS)then(kp is PS)(ki is NS)(kd is NS) (e is ZE)and(ec is Z)then(kp is Z)(ki is Z)(kd is NS) (e is ZE)and(ec is PS)then(kp is NS)(ki is PS)(kd is NS) (e is ZE)and(ec is PM)then(kp is NM)(ki is PM)(kd is NS) (e is ZE)and(ec is PB)then(kp is NM)(ki is PM)(kd is ZE) (e is PS)and(ec is NB)then(kp is PS)(ki is NM)(kd is ZE) (e is PS)and(ec is NM)then(kp is PS)(ki is NS)(kd is ZE) (e is PS)and(ec is NS)then(kp is ZE)(ki is ZE)(kd is ZE) (e is PS)and(ec is Z)then(kp is NS)(ki is PS)(kd is ZE) (e is PS)and(ec is PS)then(kp is NS)(ki is PS)(kd is ZE) (e is PS)and(ec is PM)then(kp is NM)(ki is PM)(kd is ZE) (e is PS)and(ec is PB)then(kp is NM)(ki is PB)(kd is ZE) (e is PM)and(ec is NB)then(kp is PS)(ki is Z)(kd is PB) (e is PM)and(ec is NM)then(kp is ZE)(ki is Z)(kd is PS) (e is PM)and(ec is NS)then(kp is NS)(ki is PS)(kd is PS) (e is PM)and(ec is Z)then(kp is NM)(ki is PS)(kd is PS) (e is PM)and(ec is PS)then(kp is NM)(ki is PM)(kd is PS) (e is PM)and(ec is PM)then(kp is NM)(ki is PB)(kd is PS) (e is PM)and(ec is PB)then(kp is NB)(ki is PB)(kd is PB) (e is PB)and(ec is NB)then(kp is ZE)(ki is Z)(kd is PB) (e is PB)and(ec is NM)then(kp is ZE)(ki is Z)(kd is PM) (e is PB)and(ec is NS)then(kp is NM)(ki is PS)(kd is PM) (e is PB)and(ec is Z)then(kp is NM)(ki is PM)(kd is PM) (e is PB)and(ec is PS)then(kp is NM)(ki is PM)(kd is PS) (e is PB)and(ec is PM)then(kp is NB)(ki is PB)(kd is PS) (e is PB)and(ec is PB)then(kp is NB)(ki is PB)(kd is PB) 模糊 PID 仿真圖像如圖 48(af)所示： （ a） 模糊變量 pK 仿真圖像 (b)模糊變量 iK 仿真圖像 (c)模糊變量 dK 仿真圖像 (d)控制量 U 仿真圖像 (e)水位偏差 E 變化仿真圖像 (f)汽包液位模糊 PID 仿真圖像 結(jié)論： 通過(guò)對(duì)鍋爐水位分別采用模糊 PID控制系統(tǒng)和單純采用 PID控制的控制系統(tǒng)的兩種方案進(jìn)行仿真對(duì)比驗(yàn)證，從仿真圖像 可以看出模糊PID 有以下優(yōu)點(diǎn)： （ 1）汽包水位偏差 E 從震蕩到穩(wěn)定，響應(yīng)時(shí)間短，水位偏差變化明顯變小。然而在實(shí)際汽包水位控制應(yīng)用中要控制一個(gè)執(zhí)行機(jī)構(gòu)（如閥門開度），只能在某一時(shí)刻對(duì)應(yīng)有一個(gè)確定的控制量，這就必須要從模糊輸出的隸屬函數(shù)中找出一個(gè)最能代表這個(gè)模糊集合即模糊控制作用可能性分布的精確值，這就是模糊量的去模糊及清晰化。還必須將精確量轉(zhuǎn)換到為控制對(duì)象所能接受的基本論域中，這個(gè)轉(zhuǎn)換可以通過(guò)量化因子和 比例 因子來(lái)實(shí)現(xiàn)。 表 41 模糊變量 E 的隸屬度賦值表 NB NM NS ZE PS PM PB NB PB PM PM PS PS ZE ZE NN PB PB PM PS ZE ZE NS NS PM PM PM PS ZE NS NS ZE PM PM PS ZE NS NM NM PS PS PS ZE NS NS NM NM PM PS ZE NS NM NM NM NB PB ZE ZE NM NM NM NB NB 表 42 模糊變量 EC 的隸屬度賦值表 NB NM NS ZE PS PM PB NB NB NB NM NM NS ZE ZE NN MB NB NM NS NS ZE ZE NS NB NM NS NS ZE PS PS ZE NB NM NS ZE PS PM PM PS NM NS ZE PS PS PM PB PM ZE ZE PS PS PM PM PB PB ZE ZE PS PM PM PB PB E EC U E EC U 表 43 模糊變量 U 的隸屬度賦值表 NB NM NS ZE PS PM PB NB PB PM PM PS PS ZE ZE NN PB PB PM PS ZE ZE NS NS PM PM PM PS ZE NS NS ZE PM PM PS ZE NS NM NM PS PS PS ZE NS NS NM NM PM PS ZE NS NM NM NM NB PB ZE ZE NM NM NM NB NB 可以在 MATLAB的 SIMULINK中的 Fuzzy仿真工具箱中建立輸入變量與輸出變量的隸屬度函數(shù)。估計(jì)入水量與蒸汽流量間的平衡關(guān)系，然后操作主控入水閥以決定入水量是否需要增加或減少。 對(duì)應(yīng)的模糊論域?yàn)?: U={7， 6， 5,4， 3， 2， 1, 0, 1, 2, 3, 4, 5, 6, 7,} 現(xiàn)場(chǎng)操作人員調(diào)節(jié)控制汽包水位需要的過(guò) 程參數(shù)有三個(gè) :汽包實(shí)際水位與水位設(shè)定值的偏差、給水量的變化值和蒸汽量的變化值。設(shè)輸入水位偏差用模糊語(yǔ)言變量的模糊集E 表示，即 : E = { NB, NM, NS, ZE, PS, PM, PB} 其中 NB 表示實(shí)際水位 比給定水位很高， NM 表示實(shí)際水位比給定水位高， NS 表示實(shí)際水位比給定水位有點(diǎn)高， ZE 表示實(shí)際水位于給定水位相等， PS 表示實(shí)際水位比給水位有點(diǎn)低， PM 表示實(shí)際水位比給定水位低， PB 實(shí)際水位比給定水位很低。反之，則閥門關(guān)閉為“負(fù)” 。當(dāng) k時(shí)刻的水位偏差高于 kl時(shí)刻的水位偏差，說(shuō)明水量變化在增大，即實(shí)際水位有上漲趨勢(shì)，偏差變化為“負(fù)”；相反，當(dāng) k 時(shí)刻的水位偏差低于 k1 時(shí)刻的水位偏差，偏差變化為“正”。相反， y(k)低于 yr(k)時(shí)，即實(shí)際水位低于給定水位，偏差為“正”，水位低得越多，則偏差正得越大。 對(duì)于鍋爐汽包水位的模糊控制系統(tǒng)，我們采用常見的二維模糊控制器，即它的輸入變量是給定水位和實(shí)際水位的偏差及偏差 的變化 : ( ) ( ) ( )re k y k y k?? （ 4— 5） ( ) ( ) ( 1)ec k e k e k? ? ? （ 4— 6）