變頻電機與工頻電機有什么區別

變頻電機與工頻電機有什么區(qu)別

 一、普通異步(bu)電(dian)動機(ji)都是按(an)恒頻(pin)恒壓設計的，不可能完全適(shi)應變頻(pin)調速的要求。以下為變頻(pin)器對電(dian)機(ji)的影響  

 1、電動機的效率和溫(wen)升的問題   

    不(bu)論那種形(xing)式的(de)(de)變(bian)頻器，在運行中均產生(sheng)(sheng)不(bu)同程度的(de)(de)諧(xie)(xie)波(bo)(bo)電(dian)(dian)(dian)(dian)壓(ya)和電(dian)(dian)(dian)(dian)流，使(shi)(shi)電(dian)(dian)(dian)(dian)動機(ji)(ji)在非正(zheng)弦電(dian)(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)(dian)流下運行。拒資料介紹，以目前(qian)普(pu)(pu)遍(bian)使(shi)(shi)用的(de)(de)正(zheng)弦波(bo)(bo)PWM型變(bian)頻器為(wei)例，其低(di)次諧(xie)(xie)波(bo)(bo)基本(ben)為(wei)零(ling)，剩下的(de)(de)比載波(bo)(bo)頻率(lv)(lv)大一倍左(zuo)右的(de)(de)高(gao)次諧(xie)(xie)波(bo)(bo)分量為(wei)：2u+1（u為(wei)調制比）。 高(gao)次諧(xie)(xie)波(bo)(bo)會引起電(dian)(dian)(dian)(dian)動機(ji)(ji)定子(zi)(zi)銅耗(hao)、轉(zhuan)子(zi)(zi)銅（鋁）耗(hao)、鐵耗(hao)及附(fu)加損耗(hao)的(de)(de)增(zeng)加，醉為(wei)顯著的(de)(de)是轉(zhuan)子(zi)(zi)銅（鋁）耗(hao)。因為(wei)異步(bu)(bu)電(dian)(dian)(dian)(dian)動機(ji)(ji)是以接(jie)近于(yu)基波(bo)(bo)頻率(lv)(lv)所(suo)對應(ying)(ying)的(de)(de)同步(bu)(bu)轉(zhuan)速旋(xuan)轉(zhuan)的(de)(de)，因此(ci)，高(gao)次諧(xie)(xie)波(bo)(bo)電(dian)(dian)(dian)(dian)壓(ya)以較(jiao)大的(de)(de)轉(zhuan)差切(qie)割轉(zhuan)子(zi)(zi)導條后，便會產生(sheng)(sheng)很大的(de)(de)轉(zhuan)子(zi)(zi)損耗(hao)。除(chu)此(ci)之外(wai)，還(huan)需考慮因集膚效(xiao)應(ying)(ying)所(suo)產生(sheng)(sheng)的(de)(de)附(fu)加銅耗(hao)。這些(xie)損耗(hao)都會使(shi)(shi)電(dian)(dian)(dian)(dian)動機(ji)(ji)額外(wai)發熱，效(xiao)率(lv)(lv)降(jiang)低(di)，輸出(chu)功率(lv)(lv)減小，如將(jiang)普(pu)(pu)通三相異步(bu)(bu)電(dian)(dian)(dian)(dian)動機(ji)(ji)運行于(yu)變(bian)頻器輸出(chu)的(de)(de)非正(zheng)弦電(dian)(dian)(dian)(dian)源條件下，其溫升一般要增(zeng)加10%--20%。  

  2、電動機絕緣強度問題(ti)   

    目前中小型變(bian)頻(pin)器(qi)，不少是采用PWM的(de)(de)(de)(de)(de)控制方式。他的(de)(de)(de)(de)(de)載波(bo)頻(pin)率約(yue)為(wei)幾千(qian)到(dao)十(shi)幾千(qian)赫，這就(jiu)使得(de)電(dian)(dian)動(dong)(dong)機(ji)(ji)定(ding)子(zi)繞(rao)組(zu)要(yao)承(cheng)受(shou)(shou)很(hen)(hen)高的(de)(de)(de)(de)(de)電(dian)(dian)壓(ya)上升率，相當于對電(dian)(dian)動(dong)(dong)機(ji)(ji)施(shi)加陡度很(hen)(hen)大的(de)(de)(de)(de)(de)沖(chong)擊電(dian)(dian)壓(ya)，使電(dian)(dian)動(dong)(dong)機(ji)(ji)的(de)(de)(de)(de)(de)匝間絕緣承(cheng)受(shou)(shou)較為(wei)嚴酷(ku)的(de)(de)(de)(de)(de)考驗。另外，由PWM變(bian)頻(pin)器(qi)產(chan)生的(de)(de)(de)(de)(de)矩形斬波(bo)沖(chong)擊電(dian)(dian)壓(ya)疊加在電(dian)(dian)動(dong)(dong)機(ji)(ji)運行電(dian)(dian)壓(ya)上，會對電(dian)(dian)動(dong)(dong)機(ji)(ji)對地絕緣構成威脅，對地絕緣在高壓(ya)的(de)(de)(de)(de)(de)反復沖(chong)擊下會加速老化。  

  3、諧波電磁噪聲(sheng)與震動   

    普通(tong)異步電(dian)(dian)(dian)動(dong)(dong)機(ji)采用變頻(pin)器(qi)供電(dian)(dian)(dian)時(shi)，會(hui)使由(you)電(dian)(dian)(dian)磁(ci)(ci)、機(ji)械、通(tong)風等因素所引起的(de)震動(dong)(dong)和(he)噪聲變的(de)更(geng)加(jia)復(fu)雜。變頻(pin)電(dian)(dian)(dian)源中含(han)有(you)的(de)各(ge)次時(shi)間諧波(bo)與電(dian)(dian)(dian)動(dong)(dong)機(ji)電(dian)(dian)(dian)磁(ci)(ci)部分的(de)固(gu)有(you)空間諧波(bo)相互干涉，形(xing)成各(ge)種(zhong)電(dian)(dian)(dian)磁(ci)(ci)激振(zhen)(zhen)力。當電(dian)(dian)(dian)磁(ci)(ci)力波(bo)的(de)頻(pin)率(lv)(lv)和(he)電(dian)(dian)(dian)動(dong)(dong)機(ji)機(ji)體的(de)固(gu)有(you)振(zhen)(zhen)動(dong)(dong)頻(pin)率(lv)(lv)一致或接近(jin)時(shi)，將產生共振(zhen)(zhen)現象，從(cong)而加(jia)大噪聲。由(you)于電(dian)(dian)(dian)動(dong)(dong)機(ji)工作頻(pin)率(lv)(lv)范(fan)圍寬，轉速變化范(fan)圍大，各(ge)種(zhong)電(dian)(dian)(dian)磁(ci)(ci)力波(bo)的(de)頻(pin)率(lv)(lv)很難避開(kai)電(dian)(dian)(dian)動(dong)(dong)機(ji)的(de)各(ge)構件的(de)固(gu)有(you)震動(dong)(dong)頻(pin)率(lv)(lv)。  

  4、電動(dong)機對頻繁啟動(dong)、制動(dong)的(de)適應能力   

    由于采用變頻器(qi)供電(dian)(dian)后，電(dian)(dian)動(dong)(dong)(dong)機(ji)可以在很(hen)低的(de)頻率和(he)(he)電(dian)(dian)壓下以無沖擊(ji)電(dian)(dian)流的(de)方(fang)式啟動(dong)(dong)(dong)，并可利用變頻器(qi)所供的(de)各(ge)種制(zhi)動(dong)(dong)(dong)方(fang)式進(jin)行快速(su)(su)制(zhi)動(dong)(dong)(dong)，為實現(xian)頻繁啟動(dong)(dong)(dong)和(he)(he)制(zhi)動(dong)(dong)(dong)創造了條件，因而電(dian)(dian)動(dong)(dong)(dong)機(ji)的(de)機(ji)械(xie)系(xi)(xi)統和(he)(he)電(dian)(dian)磁(ci)系(xi)(xi)統處于循環交變力的(de)作用下，給機(ji)械(xie)結構(gou)和(he)(he)絕緣結構(gou)帶來疲勞和(he)(he)加速(su)(su)老(lao)化問題。  

  5、低(di)轉速(su)時的冷卻問題   

    首先，異步電動機的(de)(de)阻抗不盡(jin)理(li)想，當(dang)電源(yuan)頻率較底(di)時(shi)，電源(yuan)中高次諧波所(suo)引(yin)起的(de)(de)損耗較大。其次，普(pu)通(tong)異步電動機再轉速降低(di)(di)時(shi)，冷(leng)(leng)卻風量(liang)與轉速的(de)(de)三次方成(cheng)比例減(jian)小，致使電動機的(de)(de)低(di)(di)速冷(leng)(leng)卻狀況(kuang)變(bian)壞(huai)，溫升急劇增加，難(nan)以實現恒轉矩輸出(chu)。