1引言

　　現(xiàn)有兩種無觸點補償式交流穩(wěn)壓電源" title="穩(wěn)壓電源">穩(wěn)壓電源在取代三相柱式交流電力穩(wěn)壓器。一種是變壓器補償式穩(wěn)壓器，其原理是用多個補償變壓器組合，通過“多全橋”變換電路，切換補償變壓器的初級頭、尾連接方式進行補償，去掉了機械傳動和觸點，提高了壽命和動態(tài)性能。補償是有級的，而且所需的補償變壓器和切換開關(guān)較多，電路相對復(fù)雜，補償精度低。另一種是PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" 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title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" 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title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM" title="PWM">PWM開關(guān)式交流穩(wěn)壓器，其原理是從輸入側(cè)取得工頻交流電壓，經(jīng)過整流、正激高頻PWM變換、相位跟蹤和轉(zhuǎn)換產(chǎn)生交流補償電壓進行補償，補償是無級的，補償精度高，響應(yīng)速度快。但電路復(fù)雜，還需要一個固定的逆補償變壓器，不易實現(xiàn)大功率應(yīng)用。我曾介紹過的PWM斬波器式交流穩(wěn)壓電源很好地克服了上述缺點，是一種很有發(fā)展前途的交流穩(wěn)壓技術(shù)，但其存在著只能穩(wěn)壓，不能消除市電電壓中諧波成分的缺點。為了擴大交流穩(wěn)壓電源的功能，我們又開發(fā)研制了利用PWM高頻逆變器" title="逆變器">逆變器進行補償?shù)亩喙δ芙涣鞣€(wěn)壓電源，這種穩(wěn)壓電源具有用戶電力綜合調(diào)節(jié)器（Custompower)的功能，使穩(wěn)壓電源的性能又上了一個臺階。

　　2 采用PWM高頻逆變器的補償式交流穩(wěn)壓電源

　　采用PWM高頻逆變器的補償式交流穩(wěn)壓電源的原理電路如圖1所示。其中補償電壓uco由單相全橋逆變器產(chǎn)生（也可以采用半橋式或推挽式逆變器），逆變器采用高頻SPWM調(diào)制。單相全橋逆變器的輸出電壓uab通過輸出變壓器Tr，把電壓uab變成補償電壓uco在Tr的次級輸出。Tr的次級串聯(lián)在主電路中以對市電電壓的變化進行補償，保持輸出電壓uo穩(wěn)定不變。圖中LFCF為低通濾波器，以濾掉逆變器輸出電壓uab中的高次諧波。變壓器Tr次級繞組的電阻和漏感以及市電電源內(nèi)阻共同組成線路阻抗Z，則當負載變化時在Z上產(chǎn)生的壓降會使輸出電壓隨之變化。ur為用正弦電壓發(fā)生器和鎖相環(huán)產(chǎn)生的標準參考電壓，鎖相環(huán)是使ur在相位上與市電電壓us同步。用瞬時值usZisur作為SPWM全橋逆變器控制電路中的調(diào)制電壓，控制電路的原理框圖如圖2所示。按此圖的高頻SPWM調(diào)制原理，當用（usZisur）作為正弦調(diào)制波時，就可以使逆變器的輸出電壓與市電電壓的變化和負載電壓的變化成比例。

圖1采用逆變器補償?shù)慕涣鞣€(wěn)壓電路

圖2 控制電路原理框圖

　　21逆變器輸出電壓的諧波分析

　　假定逆變器的直流電源電壓為Ud，載波三角波的電壓幅值為Uc，則調(diào)制比M的值為：M=（1）

　　式中：Us、Is、Ur為市電電壓us，市電電流is和基準參考電壓ur的有效值。載波比：N=，fc為三角波頻率，fs為市電電壓頻率。

　　SPWM波形如圖3所示。由此圖可知，逆變器輸出電壓uab的雙重付里葉級數(shù)表示為：

uab=ua－ub=MUdsinωt＋·cosmπ·sin〔(mN＋n)ωt〕(2)

圖3參差相位法獲得三階SPWM波

　　因為變壓器Tr的變比為ξ，故補償電壓uco的表示式為：

uco=ξMUdsinωt＋ξ·cosmπ·sin〔(mN＋n)ωt〕(3)

　　uco的頻譜如圖4所示，可知：載波比N越大，諧波頻率越高，濾波越容易，所需的LFCF的值越小，當fc=12.8kHz時，LF=10mH，CF=2μF，即可將uco中的高次諧波濾掉。

圖4補償電壓uco的頻譜和諧波分量與M的關(guān)系

　　2 考慮線路阻抗Z的補償分析

　　由于逆變器開關(guān)管的正向壓降，開關(guān)死區(qū)、變壓器Tr初級繞組的電阻及漏感和交流濾波電感LF的繞組電阻及電感的影響，會使補償電壓uco的值減小。但這種影響不大，而且是基本固定的，與負載的大小變化關(guān)系不大，因此可以通過增大變壓器Tr的變比ξ來補償。

　　由圖1考慮到線路阻抗Z時，在us>ur的情況下輸出電壓的方程式為：

uo=us－Zis－uco(4)

　　假定市電電壓中無諧波，市電輸入功率因數(shù)cosφ=1，則：us=Ussinωt,is=Issinωt，將方程式（3）uco的值以及us、is的值代入式（4）得：

uo=Ussinωt－ZIssinωt－ξMUdsinωt－cosmπ·sin〔(mN＋n)ωt〕(5)

　　用電路中低通濾波器LFCF濾掉uco中的高次諧波時，則上式變?yōu)椋?/p>

uo=Ussinωt－ZIssinωt－ξMUdsinωt（6）

       將式（1）的M值及ξ=代入式（6），則得：

uo=Ussinωt－ZIssinωt－(Us－ZIs－Ur)·sinωt=Ursinωt

　　圖5所示SPWM高頻逆變器式交流穩(wěn)壓電源有六種工作狀態(tài)：

　　us>ur＋Zis，此時uco=us－Zis－ur，輸出電壓uo=us－(us－Zis－ur)－Zis=ur

　　us us=ur，此時uco=－Zis，輸出電壓uo=us－(－Zis)－Zis=ur

　　空載（is=0)us>ur，此時uco=us－ur，輸出電壓uo=us－(us－ur)=ur

　　空載（is=0)us 空載（is=0)us=ur，此時uco=0，不補償。

圖5 SPWM高頻逆變器式交流穩(wěn)壓電源有六種工作狀態(tài)

　　從以上分析可知：當市電電壓us或負載發(fā)生變化時，用瞬時值（us－ur－Zis)作為正弦調(diào)制電壓的SPWM高頻逆變器的輸出電壓uco完全可以補償輸出電壓uo的變化，保持uo=ur不變。

　　23對市電電壓中諧波的補償假定市電電壓的數(shù)值不變，但卻含有諧波Usnsinωt，即：

　　us=Us1sinωt＋Usnsinnωt，us1=ur。

　　為了使推導(dǎo)簡化，令is=0，則調(diào)制波電壓為：

　　us－Zis－ur=us1sinωt＋Usnsinnωt－Ursinωt=Usnsinnωt(7)調(diào)制比：Mn=，則補償電壓為：=ξMnUdsinnωt＋ξ·

cosm″π·sin〔(m″N＋n′)n′ωt〕(8)

　　將us、is、的值代入式（4），用低通濾波器濾去中的更高次的諧波，并將Mn=，ξ=代入中即得：

uo=Us1sinωt＋Usnsinnωt－Usnsinnωt=Us1sinωt=Ursinωt(9)

　　由式（9）可知：當市電電壓us中含有諧波時用瞬時值(us－ur－Zis)作調(diào)制波的SPWM逆變器的輸出電壓uco即可以補償?shù)魎s中的諧波，尤其是5次以下的低次諧波。

　　此外從物理上看，由于控制電路采用的是市電電壓與純正弦波參考基準電壓ur的瞬時值進行比較，所得到的瞬時值之差作為調(diào)制波進行控制補償?shù)模斒须婋妷簎s是正弦波時，us>ur時是負補償，即us－uco；us2.4逆變器型式與參數(shù)

　　穩(wěn)壓電源中的逆變器，可以用全橋式、半橋式或推挽式，其補償效果基本相同。不用高頻SPWM調(diào)制而改用線性Delta滯環(huán)PWM控制也可以達到相同的效果。唯一應(yīng)指出的一點是逆變器的直流電源電壓一定要穩(wěn)定，它對電壓的補償精度有直接影響。變壓器Tr的變比ξ=的值取決于市電電壓的最大變化范圍，市電電壓的最大允許變化范圍為±10％，實際有的地方可高達±20％，所以變比ξ一般取（20～25)％，相應(yīng)補償變壓器Tr的容量應(yīng)取穩(wěn)壓電源標稱容量的（20～25)％。

　　3三相補償式交流穩(wěn)壓電源

　　三相補償式交流穩(wěn)壓電源的原理電路如圖6所示，它由主電路、控制電路和檢測電路三部分組成。主電路又由并聯(lián)部分、串聯(lián)部分和直流部分的濾波儲能電容 Cd三部分組成。并聯(lián)部分是由低通濾波器和三相PWM開關(guān)整流器組成，開關(guān)整流器實際上就是一個三相電壓型逆變器，它的主要作用是為串聯(lián)部分的單相補償逆變器提供整流直流電源，保持直流電容Cd上的電壓恒定。直流電容Cd起濾波和儲能作用。采用三相開關(guān)整流器的目的有兩個，一是保持市電輸入功率因數(shù) cosφ=1，并使輸入電流的波形接近正弦，以減小對市電的污染；二是可以使電能雙向流動，使逆變器負載中的無功能量可以反饋回市電電源，提高補償器的效率。此外，如果在直流電容Cd上并聯(lián)儲能蓄電池，當市電故障停電時，三相PWM開關(guān)整流器轉(zhuǎn)換到逆變狀態(tài)工作，又可以短時作為在線式UPS使用。如果再附加一部分控制電路，三相電壓型逆變器又可以作為無功補償器或有源濾波器使用，以濾掉負載電流中的諧波。串聯(lián)部分是由三個單相全橋逆變器及其輸出變壓器（亦即補償變壓器）組成，其作用就是對市電電壓的高低變化、三相不對稱、諧波、閃變等進行補償；串聯(lián)部分之所以采用三個單相逆變器及輸出變壓器，其原因有兩個，一是由于三相四線制的市電系統(tǒng)所帶的負載多數(shù)情況下是不對稱的，因此三相電壓也不對稱，必須用互無聯(lián)系的單相逆變器獨立進行補償。二是也可以提高三相四線制電源的可靠性，萬一有一相出現(xiàn)故障另外兩相還可以繼續(xù)供電。三個單相逆變器也都是可以雙向工作的，當市電電壓us等于標稱基準電壓時，三個單相逆變器由逆變的補償狀態(tài)轉(zhuǎn)換到開關(guān)整流狀態(tài)向直流電容Cd或蓄電池供電，以保證并聯(lián)電路的三相電壓型逆變器正常工作。這樣，三相交流穩(wěn)壓電源就變成了用戶電力綜合調(diào)節(jié)器（Custompower)。

圖6三相補償式交流穩(wěn)壓電源原理電路

　　三相補償式穩(wěn)壓電源的工作原理與單相相同，都是通過檢測電路將需要補償?shù)母鞣N電壓分量檢測出來進行補償，以保持輸出電壓為正弦穩(wěn)定的電壓。由于三相四線制系統(tǒng)存在著三相電壓不對稱的問題，雖然單相電路使用的正弦瞬時值比較法也可以采用，但為了能檢測出三相電壓的不對稱性，采用了基于廣義瞬時無功理論的檢測方法是更合適的，此法可以對三相四線制電路的非正弦電壓和非對稱電壓進行檢測，能更有效地檢測出三相電壓不對稱時的補償值。其原理電路如圖7所示：將檢測到的電壓信號經(jīng)過Park變換，然后通過低通濾波器濾掉d、q分量中的直流分量，最后再經(jīng)過Park反變換，即可得到三相需要補償?shù)碾妷骸?/p>

圖7廣義瞬時無功理論諧波檢測原理圖

　　3.1仿真結(jié)果

　　圖8及圖9分別為給定的三相電壓補償前和補償后的仿真波形。由這兩種波形可以看出：補償前的圖8波形的THD分別為15％、1732％、2449％，基波有不對稱現(xiàn)象。補償后的圖9波形的THD下降到3％以內(nèi)，是一組比較理想的正弦波，基波的不對稱現(xiàn)象也基本消除了。

圖8補償前的三相電壓仿真波形

圖9補償后的三相電壓仿真波形

　　3.2實驗結(jié)果

　　為了進一步驗證補償效果，又進行了實驗。實驗參數(shù)為：變壓器變比為1∶4；串聯(lián)部分電路的濾波器參數(shù)為：LF=10mH,CF=2μF；并聯(lián)部分電路的濾波器參數(shù)為：LF=10mH,CF=1μF。串聯(lián)部分及并聯(lián)部分逆變器的開關(guān)管為PM50RSK060，開關(guān)頻率為12.8kHz，標準電壓有效值為110V（峰值為15556V），頻率為50Hz。圖10及圖11分別為補償前和補償后A相電壓的實驗波形。圖10補償前的電壓幅值為120V（有效值為8485V）下降了2286％，而補償后的圖11的電壓幅值為154V（有效值為109V），下降1％。可見對電壓的高低變化進行了補償，補償精度為1％；THD由補償前的32％下降到補償后的27％。

圖10補償前電壓實驗波形

圖11補償后電壓實驗波形

　　4結(jié)語

　　通過仿真和實驗表明，采用PWM高頻逆變器的補償式交流穩(wěn)壓電源，既可以補償市電電壓的高低變化，也可以補償諧波和閃變等，對于三相穩(wěn)壓電源還可以補償三相電壓的不對稱，從而有效地提高了電能質(zhì)量，是一種很有前途的交流穩(wěn)壓電源。

　　適當?shù)丶尤胍恍┛刂齐娐?，還可以使其具有無功補償、有源濾波的作用。在直流電容Cd上并聯(lián)蓄電池以后，還可以當短時在線UPS使用，是一種較好的多功能電能質(zhì)量補償器，具有廣泛的用途，應(yīng)大力發(fā)展，以取代陳舊的交流穩(wěn)壓電源。