【正文】 level NPC topology. This kind of inverter can realize a whole range with a voltage rating from 2. 3 kV to 4. 1 6kV Series connection of IIVIGBT modules is used in the 3. 3 kV and 4. 1 6kV devices. The 2. 3 kV inverters need only one HVIGBT per switch[2,3]. 2. 1 Power section To meet the demands for medium voltage applications. a threelevel neutral point clamped inverter realizes the power section. In parison to a twolevel inverter. the NPC inverter offers the benefit that three voltage levels can be supplied to the output terminals, so for the same output current quality, only 1/4 of 13 the switching frequency is necessary. Moreover the voltage ratings of the switches in NPC inverter topology will be reduced to 1/2. and the additional transient voltage stress on the motor can also be reduced to 1/2 pared to that of a twolevel inverter. The switching states of a threelevel inverter are summarized in Table 1. U. V and W denote each of the three phases respectively。 the driven impeller, which acts as a centrifugal pump。 therefore. they are limited to the lowpower, simpleprofile conveyor belt drives. Reducedvoltage starters. As conveyor power requirements increase,controlling the applied motor torque during the acceleration period bees increasingly important. Because motor torque is a function of voltage, motor voltage must be controlled. This can be achieved through reducedvoltage starters by employing a silicon controlled rectifier (SCR). A mon starting method with SCR reducedvoltage starters is to apply low voltage initially to take up conveyor belt slack. and then to apply a timed linear ramp up to full voltage and belt speed. However, this starting method will not produce constant conveyor belt acceleration. When acceleration is plete. the SCRs, which control the applied voltage to the electric motor. are locked in full conduction, providing fullline voltage to the motor. Motors with higher torque and pull vp torque, can provide better starting torque when bined with the SCR starters, which are available in sizes up to 750 KW. Wound rotor induction motors. Wound rotor induction motors are connected directly to the drive system reducer and are a modified configuration of a standard AC induction motor. By inserting resistance in series with the motor39。 7 英文譯文 Belt Conveying Systems Development of driving system Among the methods of material conveying emploved, belt conveyors play a very imporient part in the reliable carrying of material over long distances at petitive cost. Conveyor systems have bee larger and more plex and drive systems have a l so been going through a process of evolution and will continue to do so. Nowadays, bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the case for the conveyor drives in Chengzhuang Mine). The ability to control drive acceleration torque is critical to belt conveyors39。 4 結(jié)論 近年來輸送機(jī)驅(qū)動(dòng)控制技術(shù)的進(jìn)步已更為可靠，符合低成本效益和高效驅(qū)動(dòng)的驅(qū)動(dòng)系統(tǒng)為用戶提供了選擇。 3 測試結(jié)果 三個(gè) 750kW/ 2. 3V 三電平逆變器在成莊煤礦 2. 動(dòng)系統(tǒng) 成功安裝之后，對整個(gè)變頻傳動(dòng)系統(tǒng) (VFC)的性能進(jìn)行了測試，測試結(jié)果顯示出使用 VFC 控制系統(tǒng)的帶式輸送機(jī)的優(yōu)良特性。它以一種優(yōu)化方式確定每一次開關(guān)時(shí)刻。圖 2 為間接矢量控制框圖圖中指令磁通甲ψ r 是速度的函數(shù)，反饋速度和前饋滑差控制信號川赫目加。 輸入端變流器 為通常使用 12 脈沖二極管整流器給直流環(huán)節(jié)電容器充電，在輸入端引入的諧波是很小的。 三電平中點(diǎn)箱位電壓型逆變器的開關(guān)狀態(tài)可歸納于表 1， U， V 和 W5 分別表示三相， P, N 和 G 是直流母線上的三個(gè)點(diǎn)。 HVIGBT 模塊串聯(lián)可使用在 3. RV 和 4. 16kV的設(shè)備。由三臺 750kW/ 的這種逆變器構(gòu)成的 VFC 系統(tǒng)已經(jīng)成功安裝在成莊煤礦長 2. 71m 二的帶式輸送機(jī)驅(qū)動(dòng)系統(tǒng)中。 VFC 驅(qū)動(dòng)4 為傳送帶啟動(dòng)提供了優(yōu)良的速度和轉(zhuǎn)矩控制，也能為多機(jī)驅(qū)動(dòng)系統(tǒng)提供負(fù)載均分。 1. 3 變頻控制 (VFC) 變頻控制也是一種直接驅(qū)動(dòng)方式，它具有非常獨(dú)特的高性能。此種液力偶合器同樣由三個(gè)標(biāo)準(zhǔn)的液力偶合單元構(gòu)成，即葉輪、渦輪和一個(gè)包含工作環(huán)路的外殼。偶合器的旋轉(zhuǎn)外殼有溢出口，允許液體不斷地從工作腔中流出進(jìn)入一個(gè)分 離的輔助腔，油從輔助腔通過一個(gè)熱交換器泵到控制偶合器充液量的電磁閥。傳遞功率可達(dá)幾千千瓦。流體從葉輪到渦輪，在從動(dòng)軸產(chǎn)生扭矩?？刂?DC 驅(qū)動(dòng)技術(shù)一般應(yīng)用 SCR 裝置，它允許連續(xù)的變速操作。在多驅(qū)動(dòng)系統(tǒng)中，一個(gè)外加的滑差電阻可能將總是串聯(lián)在轉(zhuǎn)子繞組回路中以幫助均分負(fù)載。但是，這種啟動(dòng)方式不會(huì)產(chǎn)生穩(wěn)定的加速度，當(dāng)加速完成時(shí)，控制電機(jī)電壓的 SCR2 鎖定在全導(dǎo)通，為電機(jī)提供全壓。但是，不能控制啟動(dòng)扭矩和最大停止扭矩。為了負(fù)載分配在多個(gè)驅(qū)動(dòng)上，扭矩和速度控制在驅(qū)動(dòng)系統(tǒng)的設(shè)計(jì)中也是很重要的因 素。輸送系統(tǒng)將會(huì)變得更大、更復(fù)雜，而驅(qū)動(dòng)系統(tǒng)也己經(jīng)歷了一個(gè)演變過程，并將繼續(xù)這樣下去。如今，較大的輸送帶和多驅(qū)動(dòng)系統(tǒng)需耍更大的功率，比如 3 驅(qū)動(dòng)系統(tǒng)需耍給輸送帶 750KW(成莊煤礦輸送機(jī)驅(qū)動(dòng)系統(tǒng)的要求 )。由于輸送機(jī)驅(qū)動(dòng)系統(tǒng)控制技術(shù)的進(jìn)步，目前更多