外文翻譯--永磁無刷直流電動機(jī)的最新進(jìn)展

1、<p><b>　　中文5821字</b></p><p><b>　　英 文 翻 譯</b></p><p>　　年 月 日 </p><p>　題 目:Recent advances in permanent magnet brushless DC motors &l

2、t;/p><p>　專 ?業(yè)? 班? 級:</p><p>　學(xué) ?? ?號:</p><p>　姓 ?名:</p><p>　指 導(dǎo) 教 師:</p><p>　學(xué) 院 名 稱:電氣信息學(xué)院 </p><p>　　出處：Sadhana, 1997, 22(6): 8

3、37-853</p><p><b>　　文獻(xiàn)翻譯</b></p><p>　　永磁無刷直流電動機(jī)的最新進(jìn)展</p><p>　　BHIM SINGH</p><p>　　電氣工程技術(shù)學(xué)院，印度理工大學(xué)，Hauz Khas，新德里110016，印度</p><p>　　電子郵箱：bsingh @

4、ee.iitd.ernet.in</p><p>　　摘要 本文論述了永磁無刷直流（PMBLDC）電機(jī)驅(qū)動的最新發(fā)展成果，并作出對先進(jìn)水平的各類電機(jī)的建設(shè)、閉環(huán)控制器的位置、速度和電流/轉(zhuǎn)矩的控制以及最近趨勢的逆變器、傳感器等的綜合考量。詳細(xì)討論無機(jī)械傳感器技術(shù)，和減少轉(zhuǎn)矩脈動，噪音和振動的特殊方法，敘述在永磁無刷直流電機(jī)驅(qū)動控制中使用集成芯片的微電子影響。由于驅(qū)動器性能的改善和成本的減少，其應(yīng)用范圍在日益擴(kuò)大

5、。</p><p>　　關(guān)鍵詞 永磁無刷直流電機(jī)；傳感器；控制器；無位置傳感器運行；轉(zhuǎn)矩脈動。</p><p><b>　　1.引言</b></p><p>　　永磁無刷直流（PMBLDC）電機(jī)的應(yīng)用范圍越來越廣，如家用電器、汽車、信息技術(shù)設(shè)備、工業(yè)設(shè)備、公共生活設(shè)施、交通運輸、航空航天、國防設(shè)備、電動工具、玩具、視覺音響設(shè)備、醫(yī)療健康器材，

6、這些設(shè)備從微瓦至兆瓦不等。其性能的優(yōu)越性體現(xiàn)在：效率高、響應(yīng)速度快、重量輕、控制精準(zhǔn)、可靠性高、免維護(hù)運行、無電刷、功率密度高和體積小。最新的無刷直流電動機(jī)采用高性能稀土材料制成，應(yīng)用不同的電機(jī)結(jié)構(gòu)，如軸向場、徑向場、封裝類型、矩形反饋、正弦反饋來提高傳感器技術(shù)，加快半導(dǎo)體模塊反應(yīng)速度，降低成本，提高微電子器件性能。最新的控制理念，如擁有穩(wěn)定性好，適應(yīng)性強(qiáng)的模糊神經(jīng)網(wǎng)絡(luò)控制器，對于其在轉(zhuǎn)速為每分鐘幾轉(zhuǎn)到幾千轉(zhuǎn)的范圍內(nèi)的廣泛使用是一個福音

7、。他們已被證明在機(jī)床、機(jī)器人技術(shù)和高精度伺服系統(tǒng)，以及各種工業(yè)和過程控制中的速度控制和轉(zhuǎn)矩控制的應(yīng)用上最適用于位置控制。</p><p>　　盡管永磁無刷直流電機(jī)是電機(jī)中的佼佼者，但它在目前看來依舊面臨著許多障礙，如大量零部件帶來的成本、轉(zhuǎn)矩脈動、噪音、振動而降低了可靠性的問題，還有操作上的限制，如溫度升高等。為了克服這些問題，已經(jīng)在驅(qū)動器的各個方面做了堅持不懈的努力。永磁無刷直流電機(jī)本身無疑有著相當(dāng)大的使命；本

8、文集中討論從電機(jī)結(jié)構(gòu)、閉環(huán)控制器、半導(dǎo)體功率模塊、傳感器和無傳感器、轉(zhuǎn)矩脈動最小化、微電子影響、降低成本和潛在的應(yīng)用這些方面來講，永磁無刷直流電機(jī)的最新進(jìn)展。</p><p>　　2.永磁無刷直流電機(jī)的最新發(fā)展</p><p>　　在各種電機(jī)中永磁激勵已代替了直流勵磁，如直流電機(jī)、同步電機(jī)和新型永磁無刷電機(jī)如永磁步進(jìn)電機(jī)、混合步進(jìn)電機(jī)和永磁無刷直流電機(jī)。高成本的永磁材料是電機(jī)使用和發(fā)展的主

9、要瓶頸。更好的永磁材料、日益提高的制造工藝、電機(jī)為了滿足特定的應(yīng)用而設(shè)計的不同的構(gòu)造使其成為目前最好的電機(jī)。永磁電機(jī)的范圍很廣，本文僅限永磁無刷直流電機(jī)。</p><p>　　目前永磁無刷直流電機(jī)中的永磁材料可以分為以下三種：鋁鎳鈷（A1-Ni-Co-Fe），陶瓷包括鐵氧體和稀土材料，如釤-鈷（Sm-Co）、釹-鐵-硼（Nd-Fe-B）。鋁鎳鈷和鐵氧體早已在永磁電機(jī)中使用，因為它們便宜且容易獲得。稀土永磁材料，即

10、釤鈷，由于其高剩余磁通密度、抗磁力和低溫度系數(shù)造成的高能量密度，目前也投入使用。釹鐵硼被認(rèn)為是目前最好的永磁材料之一，因為它提供了更高的剩余磁通密度和抗磁力，然而，它唯一的缺點是其溫度界限，目前正在不斷努力克服這一點，這也將使得永磁無刷直流電機(jī)擁有更高的效率和更小的規(guī)模等優(yōu)點。</p><p>　　永磁無刷直流電機(jī)可分為不同的類別，例如相數(shù)、徑向或軸向場、無保持架或帶保持架桿，表面安裝永磁鐵或埋入磁鐵，正弦波或矩

11、形饋電機(jī)等，其中一部分在本章會作簡要討論。</p><p><b>　　2.1相數(shù)</b></p><p>　　永磁無刷直流電機(jī)的管軸流風(fēng)機(jī)設(shè)計為低功率單相（<50W），用于冷卻電子設(shè)備。它在太陽能光伏反饋制冷系統(tǒng)，伺服控制等家用電器中為兩相結(jié)構(gòu)。大部分的中，高功率的電機(jī)被設(shè)計成類似于傳統(tǒng)的交流電機(jī)三相結(jié)構(gòu)。在一些電動車和潛艇推進(jìn)器等兆瓦等級電動機(jī)中，設(shè)計師為了

12、降低每相的功率處理要求將相數(shù)增加至五個，六個或更多。</p><p>　　2.2徑向和軸向場電機(jī)</p><p>　　市面上大多數(shù)電機(jī)都是徑向場類型（圓柱形或凸極構(gòu)造）。然而，軸向場電機(jī)在功率密度，轉(zhuǎn)矩慣量比，峰值扭力，磁鐵重量少，電感低，繞組匝數(shù)少，設(shè)計緊湊等方面比傳統(tǒng)的徑向構(gòu)造更有優(yōu)勢。軸向場電機(jī)設(shè)計為包裹，磁盤和三明治型結(jié)構(gòu)，并且轉(zhuǎn)子中沒有鐵，這使得慣性降低。在軸向場電機(jī)中，軸向磁場

13、是由轉(zhuǎn)子磁鐵與徑向電流的相互作用產(chǎn)生的，磁鐵被封裝在樹脂或塑料殼內(nèi)。由于它們的性能，它們被認(rèn)為最適用于機(jī)器人技術(shù)，計算機(jī)設(shè)備和機(jī)床等。徑向場電機(jī)的設(shè)計也有不同的磁鏈波形，如正弦波或梯形波，不同的形狀和位置的轉(zhuǎn)子磁鐵，例如深埋或表面安裝等。因為定子設(shè)計類似于常規(guī)交流同步或異步電動機(jī)，它們被廣泛使用。圖1顯示了這兩種類型的流行永磁無刷直流電動機(jī)的典型橫截面。</p><p>　　2.3轉(zhuǎn)子內(nèi)永磁鐵的形狀和位置<

14、/p><p>　　在永磁無刷直流電機(jī)中永磁鐵放置于轉(zhuǎn)子內(nèi)。在軸向場電機(jī)中，磁體被封裝在圓盤狀的樹脂或塑料內(nèi)，如圖所示，這些磁體是為了誘發(fā)正弦波或梯形波的反電動勢而被這樣放置。在徑向場電機(jī)中，永磁體的放置方式不同，例如在低速電機(jī)中表面貼裝，而在高速永磁無刷電機(jī)中放置在內(nèi)部徑向方向或切向方向，圖2顯示出了這種轉(zhuǎn)子的幾何形狀。根據(jù)應(yīng)用程序，它們還能實現(xiàn)正弦或梯形反電動勢。</p><p>　　2.4

15、正弦和矩形反饋電機(jī)</p><p>　　永磁無刷直流電機(jī)設(shè)計成有正弦或梯形波（激發(fā)）引起反電動勢。正弦電機(jī)需通入多相交流電流，類似于傳統(tǒng)同步電動機(jī)，能夠通過頻率控制恒轉(zhuǎn)矩運行于基速之下，并擁有相同的無紋波轉(zhuǎn)矩和功率因數(shù)，在恒功率運行條件下能夠通過電流影響磁場的削弱。運行速度限制為會由電樞反應(yīng)和機(jī)械結(jié)構(gòu)引起的退磁的最大速度。轉(zhuǎn)子的磁性特點為磁阻轉(zhuǎn)矩有助于加寬恒功率運行速度范圍。梯形激發(fā)電機(jī)需要具有120度電寬度和可

16、調(diào)節(jié)大小和方向的多相位均衡矩形電流。磁與恒定振幅多相電流不斷相互作用形成類似于電子換相的傳統(tǒng)直流電機(jī)的無紋波轉(zhuǎn)矩。因為這些矩形電流，他們也被稱為開關(guān)永磁電機(jī)、無刷直流電機(jī)和電子換向永磁無刷直流電動機(jī)。</p><p>　　圖3為這兩種類型的電機(jī)的理想電流波形。位置傳感器是根據(jù)在電機(jī)繞組中的自同步控制模式來實現(xiàn)這些理想的電流波形的要求而變化。</p><p><b>　　閉環(huán)控制器

17、</b></p><p>　　不論正弦或梯形激勵，永磁無刷直流電機(jī)在運動控制應(yīng)用中用于位置控制，速度控制和轉(zhuǎn)矩控制。圖4示出了一個典型的位置閉環(huán)控制內(nèi)的速度和電流回路。速度控制系統(tǒng)外位置環(huán)是不需要的，且速度給定是命令信號。轉(zhuǎn)矩控制與高性能運動控制結(jié)合，其通過同步相電流和軸的位置反饋進(jìn)行閉環(huán)調(diào)節(jié)。在大多數(shù)永磁無刷直流電機(jī)中，轉(zhuǎn)矩與電流是線性相關(guān)的，并且轉(zhuǎn)矩指令只用一個簡單的比例常數(shù)即可映射到當(dāng)前指令。在

18、特殊情況下，轉(zhuǎn)矩和電流指令之間為非線性映射。永磁無刷直流電機(jī)驅(qū)動的恒功率運行是通過弱磁控制技術(shù)，這也要求轉(zhuǎn)矩與電流映射的另一個命令信號。永磁無刷直流電機(jī)相繞組的電流調(diào)節(jié)無論是正弦波還是矩形波方式都是利用電流控制電壓源逆變器（VSI）實現(xiàn)的。脈寬調(diào)制是用于發(fā)出開關(guān)信號給逆變器從而實現(xiàn)繞組電流與命令電流一致的滯后和預(yù)測電流的控制器。速度控制一般是使用速度反饋和速度指令實現(xiàn)的，速度指令是通過速度控制器給轉(zhuǎn)矩控制器輸出的指令信號。位置控制的實現(xiàn)

19、是通過位置控制器的位置反饋和位置命令實現(xiàn)的，位置控制器的輸出是內(nèi)部速度環(huán)的速度指令。位置和速度閉環(huán)控制器都是使用不同寬度的閉環(huán)控制器，比如PI（比例-積分）、PID（比例-積分-微分）、</p><p>　　這些經(jīng)典（PI或PID）控制器或先進(jìn)的閉環(huán)控制器，如SMC、模糊和神經(jīng)網(wǎng)絡(luò)控制器都是采用DSP、微處理器和專用集成芯片（ASIC）來實現(xiàn)速度和位置控制。許多制造商已經(jīng)開發(fā)ASIC用于永磁無刷直流電動機(jī)的典型應(yīng)

20、用。</p><p>　　逆變器和轉(zhuǎn)換器的最近發(fā)展</p><p>　　永磁無刷直流電機(jī)均是由變頻逆變器提供電子換向。在小功率的變頻器中，基于場效應(yīng)晶體管的虛擬交換接口用來實現(xiàn)理想的電流控制和合理的高開關(guān)頻率。在中等功率的變頻器中，基于場效應(yīng)晶體管的虛擬交換接口用來服務(wù)于永磁無刷直流電機(jī)。由于GTO型逆變器的自整流功能和電流控制的改進(jìn)，它被用于高功率的永磁無刷直流電機(jī)中。在中、高額定功率額

21、永磁無刷直流電機(jī)中，輸入功率因數(shù)整流器PWM電流控制是用來實現(xiàn)穩(wěn)壓直流環(huán)節(jié)和永磁無刷直流電機(jī)驅(qū)動的再生功能。經(jīng)典的PI/ PID和前饋閉環(huán)控制器用于前端轉(zhuǎn)換器的控制，它提高了交流電源的電能質(zhì)量，在電源流動的各個方向上降低了諧波和單位功率因數(shù)。</p><p>　　最近的MOSFET/IGBT為基于VSI使用模塊的形式實現(xiàn)緊湊驅(qū)動器的設(shè)計。功率MOS集成電路用于控制小功率的永磁無刷直流電機(jī)，該電機(jī)為了控制和功率放大

22、使用集成微電子去激勵電機(jī)。此外，它們的門驅(qū)動器也以模塊的形式用在了所有的保護(hù)和智能控制功能中。在一些典型的應(yīng)用（住宅商業(yè)鼓風(fēng)機(jī)）中，它們安裝非常緊湊以致全部安裝在電機(jī)外殼內(nèi)。</p><p><b>　　傳感器的最新趨勢</b></p><p>　　在永磁無刷直流電機(jī)的控制中，位置、速度和電流傳感器基本上都需要調(diào)節(jié)相電流與轉(zhuǎn)子位置同步。此外，有時端電壓傳感器也須估計任

23、一位置或速度，電壓傳感器還需要在制動或前端轉(zhuǎn)換器的控制下來調(diào)節(jié)直流母線電壓。在一些典型情況下，磁通傳感器和扭矩傳感器也使用于電機(jī)的精確控制中。這些傳感器的基礎(chǔ)性作用已經(jīng)在第三章永磁無刷直流電機(jī)驅(qū)動器的閉環(huán)控制中作了討論。在下面的部分中，會對傳感器的最新趨勢及其功能進(jìn)行簡要討論。</p><p><b>　　5.1位置傳感器</b></p><p>　　在永磁無刷直流電

24、機(jī)中，轉(zhuǎn)子磁通位置是由旋轉(zhuǎn)機(jī)械角度定義的，這是轉(zhuǎn)子位置傳感器以某種形式實現(xiàn)的。轉(zhuǎn)子磁通位置所需的相電流與轉(zhuǎn)子位置同步，還需要進(jìn)行位置控制。轉(zhuǎn)子位置使用位置傳感器直接感知或間接地使用各種測量參數(shù)估計。因此，轉(zhuǎn)子位置檢測是必不可少的電流控制永磁無刷直流電機(jī)驅(qū)動器。</p><p>　　轉(zhuǎn)子位置的感應(yīng)采用旋轉(zhuǎn)變壓器、感應(yīng)模塊絕對系統(tǒng)（IMAS）、霍爾效應(yīng)傳感器、磁敏電阻、電子和光學(xué)編碼器、同步器和角度傳感器。角度傳感器

25、是一個具有永磁場和梯形輸出波形的氣隙磁敏三相交流發(fā)電機(jī)，它用于位置和速度檢測和模擬信號輸出，可配置有4、6和8極。該編碼器的特點是每轉(zhuǎn)的脈沖數(shù)（PPR），現(xiàn)在他們應(yīng)用于幾千PPR。接口芯片也可用于將這些傳感器信號轉(zhuǎn)換成數(shù)字形式進(jìn)給數(shù)字處理器以用于永磁無刷直流電機(jī)驅(qū)動的智能控制。</p><p>　　間接位置檢測是通過運用其他測量參數(shù)，如電流和電壓來估計轉(zhuǎn)子位置實現(xiàn)的。在下一節(jié)中將會詳細(xì)描述轉(zhuǎn)子磁連位置估計的相關(guān)技

26、術(shù)。</p><p>　　5.2速度/轉(zhuǎn)速傳感器</p><p>　　在永磁直流電機(jī)驅(qū)動中，速度和速度信號基本上需要位置控制驅(qū)動器的速度控制回路和速度控制驅(qū)動器的速度反饋。速度測量由速度傳感器直接得出或用轉(zhuǎn)子位置信號估計間接得出。</p><p>　　一般的直流測速發(fā)電機(jī)和無刷測速發(fā)電機(jī)用于檢測電機(jī)的速度，它們提供了一個模擬直流電壓信號，該信號正比于軸速度。在各種類

27、型的測速發(fā)電機(jī)上電壓的極性信號反映出旋轉(zhuǎn)的方向。如今通過使用高分辨率位置傳感器或估量轉(zhuǎn)子磁通位置能夠更準(zhǔn)確地估計出轉(zhuǎn)子的速度/轉(zhuǎn)速。有時，這些傳感器不同于用于電子換向的位置傳感器。</p><p><b>　　5.3電流傳感器</b></p><p>　　高性能永磁無刷直流電機(jī)驅(qū)動的快速轉(zhuǎn)矩控制是通過與轉(zhuǎn)子磁通位置信息同步的相繞組電流的閉環(huán)調(diào)節(jié)來實現(xiàn)的，繞組電流的閉環(huán)

28、調(diào)節(jié)是通過CC-VSI的PWM或超過參考所需的感應(yīng)電流或電流控制器的滯后電流控制器實現(xiàn)的。因此，繞組電流檢測在永磁無刷直流電機(jī)的驅(qū)動中變得不可缺少。</p><p>　　電流檢測一般使用霍爾效應(yīng)電流傳感器，它檢測電流的大小和方向，并整合以提供靈敏和精確的電流檢測。非?？斓捻憫?yīng)（小于1微秒）和精確的電流傳感器在大范圍電流檢測（安培至千安的分?jǐn)?shù)）的不同廠家（ABB、LEM等）都有現(xiàn)貨。這些霍爾效應(yīng)電流傳感器有幾千伏的

29、電氣隔離，這是在高水平的驅(qū)動器中非常理想的要求。通常在三相電機(jī)中需要兩個電流傳感器，第三相電流由與電動機(jī)連接的星型結(jié)構(gòu)的其他兩相電流估計得出。這些電流調(diào)節(jié)矩形永磁無刷直流電機(jī)的電流檢測要求通常減少到在逆變器的直流鏈路的單個電流傳感器。電流分流電阻器具有低功耗，通常為了成本效益在低功率驅(qū)動器中做電流傳感器。在調(diào)制解調(diào)器的電源設(shè)備中，例如MOSFET / IGBT的電流檢測功能是許多制造商在逆變器/轉(zhuǎn)換器供給永磁無刷直流電機(jī)的控制中省去了使

30、用額外的電流傳感器。</p><p><b>　　5.4電壓傳感器</b></p><p>　　在現(xiàn)代先進(jìn)永磁無刷直流電機(jī)驅(qū)動器中，端電壓傳感技術(shù)需要估算轉(zhuǎn)子的位置和速度，故選用機(jī)械傳感器驅(qū)動以減小尺寸、成本、維護(hù)和增強(qiáng)可靠性。電壓傳感器還需要在制動過程中調(diào)節(jié)直流母線電壓，或在高規(guī)格的變頻器中用于再生功能的前端轉(zhuǎn)換器控制。端電壓檢測是通過使用電子隔離放大器（ADI公司

31、制造的AD202等）和霍爾效應(yīng)電壓傳感器（ABB制造等）的電隔離。在小規(guī)格的變頻器中，電壓檢測采用高阻值電阻分壓器來降低驅(qū)動器的成本。有時，在電機(jī)繞組的感應(yīng)電壓使用特殊繞組諸如探測線圈等來實現(xiàn)。然而，前端變換器的控制中交流電源電壓用電壓互感器感測。</p><p><b>　　傳感器的消除和減少</b></p><p>　　傳感器最新趨勢，它們的要求和可用類型的傳感器

32、已經(jīng)在第5章討論過。然而，這些傳感器在無刷直流電機(jī)驅(qū)動中可以從尺寸、成本、維護(hù)和可靠性的角度降低。通常機(jī)械轉(zhuǎn)子位置和速度傳感器的缺點是增大了電機(jī)和控制器之間的連接數(shù)量，增加了干擾，由于環(huán)境因素如溫度，濕度，震動等限制了傳感器的精度，增加了摩擦和慣性及電機(jī)外殼額外的空間。由于這些問題，在去除機(jī)械轉(zhuǎn)子位置/速度傳感器而代以利用感應(yīng)電流和電壓估算轉(zhuǎn)子位置和速度的技術(shù)上有很大的興趣和發(fā)展。而且，電壓和電流傳感器的數(shù)目可以通過在逆變器饋送永磁無刷

33、直流電機(jī)的控制中使用智能處理器來減少。這些傳感器的消除和減少的各種技術(shù)將在下面的部分作簡要討論。</p><p><b>　　6.1無機(jī)械傳感器</b></p><p>　　無轉(zhuǎn)子角位置傳感器技術(shù)是在最新發(fā)展的永磁無刷直流電機(jī)驅(qū)動中最迅速發(fā)展的新技術(shù)。在許多應(yīng)用中，無軸裝式位置傳感器是非常理想的特性，因為該傳感器是在驅(qū)動器中最昂貴和脆弱的部件之一。以下為一些無位置傳感

34、器方案的分類簡述。</p><p>　　6.2反電動勢位置估計法</p><p>　　轉(zhuǎn)子磁通位置檢測最常用的方法是根據(jù)推導(dǎo)的反電動勢信號。下面對基于反電動勢的轉(zhuǎn)子位置檢測的各種方法作簡要介紹。</p><p>　　6.2a 直接反電動勢檢測：這個方法對矩形饋永磁無刷直流電機(jī)很適用。在這些永磁電機(jī)中，特別是相繞組被激勵為每個電周期的2/3，且最好始終有一相是不被激勵

35、的。直接按順序檢測未被激勵相的反電動勢，用來產(chǎn)生與轉(zhuǎn)子磁通同步的離散的轉(zhuǎn)子位置信號電流。它已被應(yīng)用于許多工業(yè)應(yīng)用，包括磁盤驅(qū)動器、緊湊的立體聲播放機(jī)和室內(nèi)空調(diào)機(jī)。</p><p>　　6.2b 反電動勢的估算：此方法同時適用于正弦饋和矩形饋永磁無刷直流電機(jī)。此方法基于用電動機(jī)的電壓方程式重建反電動勢。反電動勢的重建既涉及模擬公式與運算放大器，也涉及運用通常用于控制的在線數(shù)字處理器來解這個方程。在這種方法中，端電壓

36、和線電流均是直接測量，且上述等式是用于實現(xiàn)反電動勢和轉(zhuǎn)子位置的估算。</p><p><b>　　b </b></p><p><b>　　a</b></p><p>　　圖1. 兩種永磁無刷直流電機(jī)橫截面 (a) 軸向電機(jī) (b) 徑向電機(jī)</p><p>　　圖2 永磁無刷直流電機(jī)的轉(zhuǎn)子幾何

37、形狀 (a) 表面安裝 (b) 內(nèi)部徑向取向 (c) 內(nèi)部磁體切向</p><p>　　圖3 (a) 正弦電機(jī)和 (b) 梯形波電機(jī)的理想電流激勵波形</p><p>　　圖4 永磁無刷直流電機(jī)速度和電流回路的閉環(huán)控制模塊圖</p><p><b>　　英文原著</b></p><p>　　Recent advances

38、 in permanent magnet brushless DC motors</p><p>　　BHIM SINGH</p><p>　　Department of Electrical Engineering, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India</p><p>

39、;　　e-mail: bsingh @ ee.iitd.ernet.in</p><p>　　Abstract. This paper deals with the latest developments in Permanent Magnet Brushless DC (PMBLDC) motor drives. A comprehensive account of the state of the art o

40、n types of construction of the motor, closed loop controllers in position, speed and current/torque control and recent trends in inverters, sensors etc. are given. Techniques for mechanical sensors elimination are discus

41、sed in detail. Special efforts made to reduce torque ripples, noise and vibrations are described. The impact of microel</p><p>　　Keywords. PMBLDC motor; sensors; controllers; sensorless operation; torque pul

42、sations.</p><p>　　1. Introduction</p><p>　　Permanent Magnet Brushless DC (PMBLDC) motors are increasingly being used in a wide spectrum of applications such as domestic equipments, automobiles,

43、information technology equipment, industries, public life appliances, transportation, aerospace, defence equipment, power tools, toys, vision and sound equipment and medical and health care equipment ranging from microwa

44、tts to megawatts . It has become possible because of their superior performance in terms of high efficiency, fast response, light</p><p>　　Inspite of being one of the best, the PMBLDC motor has faced many hu

45、rdles to come to its present stage in terms of cost, torque ripples, noise, vibrations, reduced reliability due to the large number of components, operational constraints such as temperature rise etc. Continuous efforts

46、have been made to overcome these problems on different aspects of this drive. The PMBLDC motor drive is undoubtedly quite a big mission in itself; this paper concentrates on the recent advances in PMBLDC motors i</p&g

47、t;<p>　　2. Latest developments in the PMBLDC motors</p><p>　　Permanent magnet (PM) excitation has been used in place of dc excitation in different electric machines such as dc machines, synchronous ma

48、chines and new PMBL machines such as PM stepper motors, hybrid stepper motors and PMBLDC motors. High cost of PM materials has been a major bottleneck for use and development of these electric machines. Gradual growth of

49、 better PM materials, improved manufacturing technology, varying nature of construction of these motors to suit specific applications have br</p><p>　　Presently PM materials used in PMBLDC motors are classif

50、ied in the following three broad categories, namely Alnico (A1-Ni-Co-Fe), Ceramics also include ferrites and rare-earth materials such as samarium-cobalt (Sm-Co), neodymium-iron-boron (Nd-Fe-B). Alnico and ferrites have

51、long been used in the development of PM motors as they are cheap and easily available. Rare-earth PM materials, namely SmCo, are used nowadays because of the high energy density caused by its high residual flux density,

52、coer</p><p>　　PMBLDC motors may be classified into different categories such as number of phases, radial or axial field, cageless or with cage bars, surface mounted PMs or buried magnets, sinusoidal or recta

53、ngular fed motors etc. Some of them are briefly discussed in this section.</p><p>　　2.1 Number of phases</p><p>　　PMBLDC motors are developed in single phase in low power (< 50W) for tube axi

54、al fans to cool electronics equipments. They are manufactured in two phase construction for home appliances such as solar PV fed refrigeration system, servo control etc. Most of the medium and high power rating motors ar

55、e designed in three-phase construction similar to conventional ac motors. In some electric vehicles and megawatt rating motors for submarine propulsion etc., designers have compelling reasons to increase</p><p

56、>　　2.2 Radial and axial field motors</p><p>　　Most of the motors in the market are radial field type (cylindrical or salient pole construction). However, the axial field motors have some advantages over t

57、he conventional radial field construction in terms of power density, torque to inertia ratio, peak torque, less magnet weight, low inductance, short winding turns, compact design etc. Axial field motors are designed in p

58、ackage, disk and sandwich type construction and have no iron in the rotor, resulting in low inertia. Axially directed magn</p><p>　　Radial field motors are also designed with varying desired flux linkage wav

59、eforms such as sinusoidal or trapezoidal, different shapes and positions of magnets in the rotor such as buried or surface mounted etc. They are widely used since stator design is similar to conventional ac synchronous o

60、r induction motors. Figure 1 shows the typical cross-sections of these two types of popular PMBLDC motors.</p><p>　　2.3 Shape and location of PM in rotors</p><p>　　Permanent magnets are placed i

61、n the rotor in PMBLDC motors. In axial field type of motors, the magnets are encapsulated in resin or plastic in disc form as shown in figure la. These magnets are placed in such a manner that induced back emf are either

62、 sinusoidal or trapezoidal waveforms. In radial field motors, the magnets are placed in different form such as surface mounted for low speed motors and interior radially oriented or interior tangentially oriented in high

63、 speed PMBL motors. Figure 2 s</p><p>　　2.4 Sinusoidal and rectangular fed motors</p><p>　　PMBLDC motors are designed to have either sinusoidal or trapezoidal (excited) induced back emfs. Sinuso

64、idal excited motors are fed with sinusoidal polyphase currents similar to conventional synchronous motors for ripple-free torque with unity power factor for constant torque operation below base speed with frequency contr

65、ol and having leading currents to affect field weakening for constant power operation. Maximum speed of operation is restricted with demagnetization caused by armature reaction </p><p>　　Figure 3 shows the i

66、deal current waveforms for these two types of motors. Position sensors requirement is accordingly changed to realize these ideal current waveforms in the motor windings in self synchronous control mode.</p><p&

67、gt;　　3. Closed loop controllers</p><p>　　Irrespective of sinusoidal or trapezoidal excitation, PMBLDC motors are used for position control, speed control and torque control in motion control applications. Fi

68、gure 4 shows a typical position closed loop control with inner speed and current loops. For speed control system outer position loop is not required and speed reference is the command signal. Torque control is incorporat

69、ed in high performance motion control through closed loop regulation of phase currents in synchronization with sha</p><p>　　These classical (PI or PID) controllers or advanced closed loop controllers such as

70、 SMC, fuzzy and neural network-based ones are implemented using DSP, microcontroller and specific application integrated chip (ASIC) for speed and/or position control. Many manufacturers have developed ASICs for typical

71、applications of PMBLDC motors.</p><p>　　4. Recent developments in inverters and converters</p><p>　　PMBLDC motors are invariably fed from variable frequency inverters to provide electronic commu

72、tation. At small ratings, MOSFET-based VSIs are used to achieve ideal current control with reasonable high switching frequency. In medium rating drives, IGBT-based VSIs are used to feed PMBLDC motors. GTO-based inverters

73、 are used in high power rating PMz BLDCM drives because of their self-commutating feature and improved current control. In medium and high power rating PMBLDC motors, an input unity powe</p><p>　　Recently MO

74、SFET/IGBT, based VSIs are used in module forms to achieve compact design of the drive. Power MOS ICs are used to control small rating PMBLDC motors which has integrated microelectronics for control and power amplifier to

75、 excite the motor. Moreover, their gate drives are also used in module form with all protective and intelligent control features. In some typical applications (residential commercial blower), they are made so compact tha

76、t these are fitted inside the motor housing.</p><p>　　5. Latest trends in sensors</p><p>　　In the control of PMBLDC motors, position, speed and current sensors are essentially required to regula

77、te the phase currents in synchronization with rotor position. Moreover, sometimes, terminal voltage sensors are also required to estimate either position or speed. Voltage sensors are also needed to regulate dc bus volta

78、ge during braking or for front end converter control. In some typical attempts, flux sensors and torque sensors are also used in the precise control of these motors. Basic role </p><p>　　5.1 Position sensors

79、</p><p>　　The rotor flux position in PMBLDC motors is defined by the mechanical angle of rotation, which is achieved from some form of rotor position sensors. Rotor flux position is required for phase curren

80、t synchronization and rotor position is also required for position control. Rotor position is directly sensed using position sensors or indirectly estimated using other measured parameters. Hence, rotor position sensing

81、is indispensable in current-controlled PMBLDC motor drives.</p><p>　　Rotor position is sensed using resolvers, inductive modular absolute system (IMAS), hall effect position sensor, magnetoresistors, electro

82、nics and optical encoders, synchros and tachsyn. The tachsyn is an airgap reluctance sensitive 3-phase alternator with PM field and trapezoidal output waveforms. It is used for position and velocity sensing and signal ou

83、tputs are analog. They are available in 4, 6 and 8 pole configurations. The encoders are characterised by number of pulses per revolutions (PP</p><p>　　Indirect position sensing is achieved by estimating the

84、 rotor position using other measured parameters such as currents and voltages etc. There are many techniques for rotor flux position estimation which are much detailed in the next section.</p><p>　　5.2 Speed

85、/velocity sensors</p><p>　　In the PMBLDC motor drive, speed or velocity signals are essentially required for speed control loops in position controlled drives and speed feedback for speed controlled drives.

86、Speed measurement is carded out either using speed transducers/sensors or estimated using the rotor position information either obtained through direct position sensing or through estimation.</p><p>　　In gen

87、eral dc tachogenerators and brushless tachogenerators are used to sense motor speed. They provide an analog dc voltage signal which is proportional to shaft speed. The polarity of this voltage signal in both types of tac

88、hogenerators results in the direction of rotation. Nowadays rotor velocity/speed is estimated more accurately by using high resolution position sensors or estimated rotor flux position. Sometimes, these sensors are diffe

89、rent from the position sensors used for electronic com</p><p>　　5.3 Current sensors</p><p>　　Fast torque control in high performance PMBLDC motor drives is implemented through closed loop regula

90、tion of phase winding currents in synchronization with rotor flux position information. Closed loop regulation of winding currents is realized through PWM or hysteresis current controllers of CC-VSI over the reference de

91、sired currents and sensed winding currents. Therefore, the sensing of winding currents becomes indispensable in PMBLDC motor drives.</p><p>　　The current sensing is generally carded out using hall effect cur

92、rent sensors. They detect the magnitude and direction of currents and are integrated to provide sensitive and accurate current sensing. Very fast response (less than 1 microsecond) and accurate current sensors are availa

93、ble from different manufacturers (ABB, LEM etc.) in wide range of current sensing (fractions of amperes to kiloamperes). These hall effect current transducers have galvanic isolation of several kilovolts which is a </

94、p><p>　　5.4 Voltage sensors</p><p>　　Terminal voltage sensing in modem advanced PMBLDC motor drives is required to estimate the rotor position and speed for the control, resulting in mechanical sen

95、sorless drive with a view to reduce size, cost, maintenance and enhanced reliability. Voltage sensing is also required to regulate dc bus voltage during braking or for control of front end converter used for regenerative

96、 feature in high rating drives.</p><p>　　Terminal voltage sensing is carried out by using electronic isolation amplifier (AD202 Analog Devices make etc.) and hall effect voltage sensors (ABB make etc.) with

97、galvanic isolation. In small rating drives, voltage is sensed using high valued resistor potential dividers to reduce the cost of the drive. Sometimes, induced voltage in the motor windings is achieved using special wind

98、ings such as search coils etc. However, ac mains voltages for the control of front end convener are sensed using t</p><p>　　6. Sensors elimination and reduction</p><p>　　Recent trends in sensors

99、, their requirement and types of available sensors are already discussed in § 5. However, some of these sensors in PMBLDC motor drive may be reduced from the view point of size, cost, maintenance and reliability. Ty

100、pically mechanical rotor position and speed sensors have the drawbacks of increasing the number of connections between motor and controller, increased interference, limitation in accuracy of sensors due to environmental