劉宇博 王旭東
摘 要:為了增強(qiáng)電動(dòng)汽車車載電源對(duì)負(fù)載擾動(dòng)的魯棒性,有效抑制系統(tǒng)輸出電壓的過沖,將一種改進(jìn)的滑??刂撇呗詰?yīng)用于電動(dòng)汽車車載電源控制系統(tǒng)中。為減少系統(tǒng)開關(guān)損耗,提高系統(tǒng)效率,車載電源采用 LLC 諧振變換器拓?fù)浣Y(jié)構(gòu)。利用擴(kuò)展描述函數(shù)法建立LLC諧振變換器的非線性模型,并在此基礎(chǔ)上設(shè)計(jì)滑模控制方法。選取全局積分滑模面,通過動(dòng)態(tài)的非線性滑模面,設(shè)計(jì)了整個(gè)運(yùn)動(dòng)過程中的滑動(dòng)模態(tài)運(yùn)動(dòng),顯著地改善了對(duì)負(fù)載擾動(dòng)的動(dòng)態(tài)響應(yīng)。通過仿真和實(shí)驗(yàn)證明了所提出的滑??刂撇呗杂行Ы鉀Q了傳統(tǒng)PI控制器在負(fù)載擾動(dòng)較大情況下輸出電壓過沖過大的問題,提高了電動(dòng)汽車車載電源控制系統(tǒng)動(dòng)態(tài)品質(zhì)。
關(guān)鍵詞:LLC諧振變換器;擴(kuò)展描述函數(shù)法;滑??刂?全局積分滑模面;車載電源
DOI:10.15938/j.emc.2020.03.016
中圖分類號(hào):TM 315文獻(xiàn)標(biāo)志碼:A文章編號(hào):1007-449X(2020)03-0131-07
Abstract:Aiming at the application of LLC resonant converter in electric vehicles, a sliding mode controller is proposed to improve the robustness of load disturbance and restrain the output voltage overshoot of the system. In order to improve the efficiency of the system, the LLC resonant converter used in the vehicle power supply reduced the switching loss of the system. The nonlinear model of LLC resonant converter was established by means of extended description function method. On this basis, a sliding mode control method was designed. The sliding mode motion of the whole motion of the system was realized by selecting the appropriate global integral sliding surface, and the dynamic quality was improved significantly by using the dynamic nonlinear sliding surface. Simulation and experiment show that the proposed controller can restrain the overshoot of the system more effectively than the conventional PI controller.
Keywords:LLC resonant converter; extended description function method; sliding mode control; global integral sliding mode surface; vehicle power supply
0 引 言
隨著新能源汽車的發(fā)展,車載電源高性能的需求也不斷提高。電源變換器經(jīng)常會(huì)受到大負(fù)載擾動(dòng),其變換器拓?fù)洳粌H要滿足負(fù)載需求,而且要具有高效率、高功率密度、高可靠性和低成本的特性[1-3]。LLC變壓器初級(jí)側(cè)可以實(shí)現(xiàn)全負(fù)載范圍內(nèi)開關(guān)管的ZVS,對(duì)于外界的電磁干擾較小,具有較高變換效率,適合車載電源應(yīng)用場(chǎng)合[4-7]。
LLC諧振變換器是一個(gè)多輸入、強(qiáng)耦合、非線性時(shí)變系統(tǒng)。傳統(tǒng)PI控制的參數(shù)設(shè)計(jì)在不同的工作條件下,也不可能始終保持良好的增益與相位裕度。提高控制系統(tǒng)的魯棒性和對(duì)特定動(dòng)態(tài)需求的瞬態(tài)響應(yīng)是十分必要的?;?刂疲╯liding mode control,SMC)可以提高系統(tǒng)的運(yùn)行性能,被廣泛應(yīng)用到DCDC變換器領(lǐng)域[8]利用滯環(huán)函數(shù)實(shí)現(xiàn)Buck變換器的滑??刂?,有效的控制系統(tǒng)開關(guān)頻率。文獻(xiàn)[10]通過引入自適應(yīng)前饋控制改變滯環(huán)寬度,消除輸入電壓變化對(duì)開關(guān)頻率的影響。文獻(xiàn)[11]提出將電感電流、輸出電壓及其積分設(shè)計(jì)Buck變換器的組合型滑模面,相比傳統(tǒng)的雙環(huán)PI控制,有很好的動(dòng)態(tài)響應(yīng),魯棒性強(qiáng),但是它沒有將其應(yīng)用于LLC諧振變換器中。文獻(xiàn)[12]分析了運(yùn)行參數(shù)的滑模嚴(yán)格存在條件,給出了滑??刂埔葡嗳珮虻刃WM信號(hào)函數(shù),并加入切換控制律提升魯棒控制效果。文獻(xiàn)[13]建立了移相全橋的動(dòng)態(tài)空間模型,討論了狀態(tài)空間中的滑動(dòng)運(yùn)動(dòng)、穩(wěn)態(tài)運(yùn)行條件和PWM控制函數(shù)。文獻(xiàn)[14]通過輸入輸出線性化的概念推導(dǎo)系統(tǒng)滑模面,以優(yōu)化LLC諧振變換器輸出電壓動(dòng)態(tài)響應(yīng)。
本文提出一種基于全局積分滑模面的LLC諧振變換器滑模控制策略,并用于電動(dòng)汽車車載電源DC/DC變換器恒壓模式控制系統(tǒng)中[15-16]。詳細(xì)研究LLC諧振變換器工作原理。通過擴(kuò)展函數(shù)描述法建立系統(tǒng)模型,選取全局積分滑模面,設(shè)計(jì)了整個(gè)運(yùn)動(dòng)過程中的滑動(dòng)模態(tài)運(yùn)動(dòng),實(shí)現(xiàn)系統(tǒng)整體穩(wěn)定性控制。所提出的SMC策略不僅能較好地處理LLC諧振變換器的模型中的高階非線性特性,而且對(duì)恒壓模式下系統(tǒng)大負(fù)載變化有較強(qiáng)的魯棒性,提高了系統(tǒng)的動(dòng)態(tài)性能。
1 變換器工作過程分析
針對(duì)電動(dòng)汽車車載電源高電壓輸入,低壓大電流輸出的工作特點(diǎn),選取全橋LLC諧振變換器的拓?fù)浣Y(jié)構(gòu),實(shí)現(xiàn)降低高壓輸入電路對(duì)開關(guān)管的耐壓要求。諧振變換器變壓器副邊采用全波整流,實(shí)現(xiàn)零電流關(guān)斷,滿足低電壓、大電流的高效率要求。LLC諧振變換器工作模態(tài)等效電路如圖1所示。電路中存在4個(gè)儲(chǔ)能元件:Lr,Lm,Cr,Co。其中Lr為變換器諧振電感,Lm為變換器勵(lì)磁電感,Cr為變換器諧振電容,Co為變換器輸出電容。
6 結(jié) 論
LLC諧振變換器在全負(fù)載條件下工作在軟開關(guān)狀態(tài),可以提高電源系統(tǒng)工作效率,因此被選作電動(dòng)汽車車載電源的拓?fù)浣Y(jié)構(gòu)。本文提出一種基于全局積分滑模面的滑??刂萍夹g(shù),并將其應(yīng)用于電動(dòng)汽車車載電源恒壓模式充電控制系統(tǒng)中。在通過擴(kuò)展函數(shù)描述的方法建立系統(tǒng)模型,設(shè)計(jì)滑模控制器。通過全局積分滑模的非線性滑模面實(shí)現(xiàn)系統(tǒng)的整體滑模運(yùn)動(dòng),有效地增強(qiáng)了系統(tǒng)穩(wěn)定性,提高了控制系統(tǒng)的動(dòng)態(tài)跟蹤效果。仿真與實(shí)驗(yàn)表明,所設(shè)計(jì)的控制器有效地解決了傳統(tǒng)PI控制器在負(fù)載擾動(dòng)較大的情況下過沖過大的問題,提高了電動(dòng)汽車車載電源控制系統(tǒng)動(dòng)態(tài)品質(zhì)。
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(編輯:賈志超)