李文勤 王明華 丁銳 王鐵廣 李明
摘 要:針對(duì)大棚溫度是一個(gè)離散的時(shí)滯系統(tǒng),導(dǎo)致溫度較難控制這一問(wèn)題,該研究提出一種基于滯后時(shí)間削弱器的模糊PID控制方法。首先,依據(jù)能量平衡原理建立大棚溫度的數(shù)學(xué)模型,并將其視為純滯后和一階慣性環(huán)節(jié)的組合,進(jìn)而在試驗(yàn)數(shù)據(jù)擬合的基礎(chǔ)上確定模型參數(shù);然后,采用模糊PID與滯后時(shí)間削弱器結(jié)合控制的方式,通過(guò)反饋的方式修訂系統(tǒng)模型,以降低純滯后環(huán)節(jié)對(duì)系統(tǒng)性能的影響;并以某花卉大棚為例在MATLAB中進(jìn)行建模仿真。仿真結(jié)果表明,滯后時(shí)間削弱器參與控制的模糊PID控制系統(tǒng)能有效地改善滯后環(huán)節(jié)的影響,系統(tǒng)無(wú)超調(diào)、無(wú)穩(wěn)態(tài)誤差,上升時(shí)間比PID縮短73.4%,比模糊PID縮短26.9%,且在調(diào)節(jié)時(shí)間上,帶滯后時(shí)間削弱器的模糊PID控制比傳統(tǒng)PID和模糊PID分別縮短77.4%、79%。
關(guān)鍵詞:大棚;溫度模型;模糊控制;PID;滯后時(shí)間削弱器
中圖分類(lèi)號(hào) S24? 文獻(xiàn)標(biāo)識(shí)碼 A文章編號(hào) 1007-7731(2021)20-0110-04
Fuzzy PID Control System of Greenhouse Temperature Based on Lag Time Reducer
LI Wenqin et al.
(College of Machinery and Transportation, Southwest Forestry University, Kunming 650224, China)
Abstract: Aiming at the problem that the greenhouse temperature is a discrete time-delay system, which makes it difficult to control the temperature,this paper proposes a fuzzy PID control method based on the lag-time attenuator. First,establish a mathematical model of greenhouse temperature based on the principle of heat balance, and treat it as a combination of pure lag and first-order inertia, and determine the model parameters on the basis of test data fitting; then, use fuzzy PID and lag time attenuator Combined with the control method, the system model was revised through feedback to reduce the impact of the pure lag link on the system performance; a flower greenhouse was used as an example to model and simulate in MATLAB. The simulation results show that the fuzzy PID control system with the lag time attenuator participating in the control can effectively improve the influence of the lag link. The system has no overshoot and steady-state error. The rise time is shortened by 73.4% compared with PID and 26.9% compared with fuzzy PID. In terms of adjustment time,the fuzzy PID control with lag time attenuator is shortened by 77.4% and 79% respectively than the traditional PID and fuzzy PID.
Key words: Greenhouse; Temperature model; Fuzzy control; PID; Lag time reducer
中國(guó)是一個(gè)人口大國(guó)、農(nóng)業(yè)大國(guó),隨著農(nóng)業(yè)技術(shù)的不斷發(fā)展,大棚技術(shù)得到了廣泛應(yīng)用。大棚技術(shù)的進(jìn)步不僅能提高我國(guó)農(nóng)業(yè)現(xiàn)代化水平,降低人工成本,還增加了農(nóng)作物產(chǎn)量,推動(dòng)我國(guó)經(jīng)濟(jì)發(fā)展[1,2]。但我國(guó)現(xiàn)階段大棚水平仍處于人工控制和半自動(dòng)化階段,勞動(dòng)生產(chǎn)率與控制精度仍然有很大的進(jìn)步空間[3,4]。而溫度是大棚作物生長(zhǎng)最重要的因素之一,直接關(guān)系到作物產(chǎn)量水平。作物的呼吸作用,光合作用都需要在適宜的溫度下進(jìn)行[5-7]。但在大棚環(huán)境中,溫度是一個(gè)較難控制的因素,主要是因?yàn)闇囟染哂蟹蔷€(xiàn)性、時(shí)滯性等特點(diǎn)。
目前,對(duì)大棚溫度的控制多采用PID控制和模糊控制等方法,PID控制器適用于線(xiàn)性好的系統(tǒng),但對(duì)于復(fù)雜非線(xiàn)性系統(tǒng)具有明顯的局限性;而模糊控制過(guò)度依賴(lài)專(zhuān)家經(jīng)驗(yàn),難以建立一套系統(tǒng)的控制理論來(lái)解決模糊控制的機(jī)理、穩(wěn)定性分析、系統(tǒng)設(shè)計(jì)方法等一系列問(wèn)題。采用模糊PID對(duì)大棚溫度系統(tǒng)進(jìn)行控制,不僅能解決模糊控制沒(méi)有積分項(xiàng)導(dǎo)致系統(tǒng)容易存在穩(wěn)態(tài)誤差的問(wèn)題,還能解決PID控制魯棒性不足的缺點(diǎn)。故將PID控制和模糊控制相結(jié)合,對(duì)大棚溫度控制系統(tǒng)進(jìn)一步優(yōu)化。
針對(duì)溫度控制的大滯后性,可采用Smith預(yù)估控制器和滯后時(shí)間削弱器等方法。其中,Smith預(yù)估控制器可以從理論上解決溫度大滯后性的問(wèn)題,但在控制過(guò)程中需要控制系統(tǒng)的精確模型,模型僅存在微小誤差仍會(huì)對(duì)系統(tǒng)造成較大影響,而滯后時(shí)間削弱器不僅能解決溫度系統(tǒng)中的大滯后性問(wèn)題,還能降低控制難度,故而本文采用帶滯后時(shí)間削弱器的模糊PID控制方法,以提高系統(tǒng)的運(yùn)行性能。