葉滿園 康力璇 潘濤
摘 要:混合級(jí)聯(lián)H橋多電平逆變器拓?fù)浣Y(jié)構(gòu)在采用常用的混合調(diào)制策略進(jìn)行控制時(shí)存在電流倒灌和能量反饋的問(wèn)題,在部分調(diào)制比區(qū)間內(nèi)甚至?xí)霈F(xiàn)高壓?jiǎn)卧敵龉β驶仞伒降蛪簡(jiǎn)卧默F(xiàn)象,當(dāng)?shù)蛪簡(jiǎn)卧绷鱾?cè)電壓由不控整流橋提供時(shí)會(huì)使得直流母線電容電壓上升。為解決該問(wèn)題,文中提出一種基于改進(jìn)載波層疊調(diào)制的控制方法,其中,高壓H橋單元采用方波與三角載波相結(jié)合的方法,低壓H橋單元采用改進(jìn)PD調(diào)制的方法,對(duì)混合頻率下所得脈沖進(jìn)行了重新的邏輯運(yùn)算與組合,該方法既能解決電流倒灌和能量回饋的問(wèn)題,還能使兩單元之間的輸出功率分配也得到了改善。最后進(jìn)行了仿真和實(shí)驗(yàn)結(jié)果驗(yàn)證。
關(guān)鍵詞:混合級(jí)聯(lián)H橋多電平逆變器;調(diào)制策略;電流倒灌;能量回饋;邏輯運(yùn)算
DOI:10.15938/j.emc.2020.03.009
中圖分類號(hào):TM312文獻(xiàn)標(biāo)志碼:A文章編號(hào):1007-449X(2020)03-0071-08
Abstract:The hybrid cascaded Hbridge multilevel inverter topology has the problems of current backflow and energy feedback when it is controlled by a common hybrid modulation strategy. In some modulation ratios, the output power of the highvoltage unit may even be fed back to the lowvoltage unit. when the DC side voltage of the lowvoltage unit is provided by the uncontrolled rectifier bridge, the DC bus capacitor voltage will rise. In order to avoid this problem, a method of modified carrier phase disposition modulation strategy is proposed.Among them, the highvoltage Hbridge unit adopted a method of combining a square wave and a triangular carrier, and the lowvoltage Hbridge unit adopted an improved PD modulation method, which recalculated and combined the pulses obtained at the mixed frequency. This method can solve the problems of current backflow and energy feedback, and can also improve the output power distribution between the two units. Finally, simulation and experimental results were verified.
Keywords:hybrid cascaded Hbridge multilevel inverter;modulation strategy;current backflow;energy feedback;logic operation
0 引 言
隨著電力電子與電力傳動(dòng)技術(shù)的快速發(fā)展,多電平逆變器得到了越來(lái)越多的應(yīng)用,其中級(jí)聯(lián)H橋(cascaded HBridge,CHB)多電平逆變器是最為廣泛應(yīng)用的拓?fù)渲籟1-6]。與傳統(tǒng)CHB拓?fù)湎啾?,混合?jí)聯(lián)H橋多電平逆變器拓?fù)浣Y(jié)構(gòu)因?yàn)榭梢詫?duì)不同等級(jí)電壓級(jí)聯(lián)單元進(jìn)行協(xié)同控制,因此在相同條件下逆變器輸出的電平數(shù)更多,控制策略也更為靈活性[7-9]。最早提出混合七電平逆變器拓?fù)浣Y(jié)構(gòu)的是印度學(xué)者M(jìn)anjrekar[10], 目前該拓?fù)湟呀?jīng)在包括電動(dòng)汽車[11],光伏[12-13]以及有源電力濾波器[14]等領(lǐng)域進(jìn)行了應(yīng)用,并且都取得了較好的控制效果。
脈寬調(diào)制(pulse width modulation,PWM)技術(shù)對(duì)逆變器來(lái)說(shuō)非常重要,目前多電平逆變器PWM策略主要有:低頻調(diào)制的特定諧波消除脈寬調(diào)制[15]、高頻調(diào)制的多載波PWM調(diào)制[16]和電壓空間矢量調(diào)制[17]、以及混合調(diào)制(Hybrid PWM, HPWM) [18]三大類。針對(duì)混合CHB七電平逆變器拓?fù)?,目前比較常用的調(diào)制方法是文獻(xiàn)[19]提出的傳統(tǒng)HPWM調(diào)制策略,它分別通過(guò)對(duì)高、低壓?jiǎn)卧M(jìn)行低頻和高頻的協(xié)調(diào)控制以輸出較高質(zhì)量的電壓波形,但是該方法存在電流倒灌問(wèn)題,在部分調(diào)制度區(qū)間內(nèi)甚至?xí)霈F(xiàn)能量回饋現(xiàn)象,如采用不控整流橋來(lái)提供直流電源將導(dǎo)致直流母線電容電壓上升。為了解決能量倒灌問(wèn)題,就需要采用全控橋電路來(lái)提供電源,但是這樣會(huì)增加電路成本,降低系統(tǒng)的可靠性,并且因?yàn)楦骷?jí)聯(lián)單元間輸出功率分配有可能輸出極不均衡的現(xiàn)象,電源利用率差別也較大。文獻(xiàn)[20]通過(guò)分析電流倒灌產(chǎn)生的原因,進(jìn)而提出一種適合混合CHB七電平逆變器的調(diào)制方法,該方法能夠保證高、低壓?jiǎn)卧敵鲭妷簶O性始終相同,從而避免電流倒灌現(xiàn)象。但是該方法需要搭建相應(yīng)的驅(qū)動(dòng)信號(hào)邏輯電路來(lái)對(duì)逆變器進(jìn)行控制,降低了系統(tǒng)可靠性。
文中以兩單元混合七電平逆變器為研究對(duì)象,首先分析了HPWM策略的調(diào)制原理及輸出電壓特性,然后,通過(guò)對(duì)同相載波層疊(phase disposition,PD)策略進(jìn)行優(yōu)化,提出一種改進(jìn)的PD調(diào)制方法,該方法通過(guò)重構(gòu)三角載波,并適當(dāng)引入邏輯控制來(lái)得到混合CHB逆變器所需的觸發(fā)脈沖,從而完全解決了電流倒灌問(wèn)題,且而還能夠改善了高壓?jiǎn)卧偷蛪簡(jiǎn)卧妮敵龉β史峙洹?/p>
5 結(jié) 論
本文對(duì)混合H橋級(jí)聯(lián)七電平逆變器的調(diào)制策略進(jìn)行了研究,分析了傳統(tǒng)HPWM存在的問(wèn)題和產(chǎn)生的原因。針對(duì)該問(wèn)題提出一種改進(jìn)PD調(diào)制方法,該方法能夠避免兩單元輸出電壓極性相反的情況,有效的解決了傳統(tǒng)HPWM策略中存在電流倒灌和功率回饋的問(wèn)題。該方法實(shí)現(xiàn)簡(jiǎn)單、運(yùn)算量小,同時(shí)能夠保證逆變器的輸出波形質(zhì)量,對(duì)混合級(jí)聯(lián)七電平的實(shí)際應(yīng)用具有一定的意義。
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(編輯:賈志超)