【正文】 drives． Reducedvoltage starters． As conveyor power requirements increase， controlling the applied 第 2 頁 motor torque during the acceleration period bees increasingly important． Because motor torque 1s 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 fu11line voltage to the motor． Motors with higher torque and pull—up 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 motor’s rotor windings． the modified motor control system controls motor torque． For conveyor starting， resistance is placed in series with the rotor for low initial torque． As the conveyor accelerates， the resistance is reduced slowly to maintain a constant acceleration torque． On multipledrive systems． an external slip resistor may be left in series with the rotor windings to aid in load sharing． The motor systems have a relatively simple design． However, the control systems for these can be highly plex， because they are based on puter control of the resistance switching． Today， the majority of control systems are custom designed to meet a conveyor system’s particular specifications． Wound rotor motors are appropriate for systems requiring more than 400 kW ． DC motor． DC motors． available from a fraction of thousands of kW ， are designed to deliver constant torque below base speed and constant kW above base speed to the maximum allowable revolutions per minute(r/min)． with the majority of conveyor drives, a DC shunt wound motor is used． Wherein the motor’s rotating armature is connected externally． The most mon technology for controlling DC drives is a SCR device． which allows for continual variablespeed operation． The DC drive system is mechanically simple, but can include plex customdesigned electronics to monitor and control the plete system． This system option is expensive in parison to other softstart systems． but it is a reliable, costeffective drive in applications in which torque,1oad sharing and variable speed are primary considerations． DC motors generally are used with higherpower conveyors， including plex profile conveyors 第 3 頁 with multipledrive systems， booster tripper systems needing belt tension control and conveyors requiring a wide variablespeed range． 1． 2 Hydrokiic coupling Hydrokiic couplings， monly referred to as fluid couplings． are posed of three basic elements。如今，較大的輸送帶和多驅(qū)動系統(tǒng)需要更大的功率 ,比如 3 驅(qū)動系統(tǒng)需要給輸送帶750KW (成莊煤礦輸送機(jī)驅(qū)動系統(tǒng)的要求 )。由于輸送機(jī)驅(qū)動系統(tǒng)控制技術(shù)的進(jìn)步 ,目前更多可靠的低成本和高效驅(qū)動的驅(qū)動系統(tǒng)可供顧客選擇 [1]。但是 ， 不能控制啟動扭矩和最大停止扭矩。但是 ， 這種啟動方式不會產(chǎn)生穩(wěn)定的加速度 ， 當(dāng)加速完成時 ,控制電機(jī)電壓的 SCR 鎖定在全導(dǎo)通 ， 為電機(jī)提供全壓。在多驅(qū)動系統(tǒng)中 ， 一個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。 第 9 頁 直流 (DC)電 機(jī) 大多數(shù)傳送驅(qū)動使用 DC 并勵電機(jī) ， 電機(jī)的電樞在外部連接。 液力偶合器 流體動力偶合器通常被稱為液力偶合器 ， 由三個基本單元組成 ： 充當(dāng)離心泵的葉輪 ,推 進(jìn)水壓的渦輪和裝進(jìn)兩個動力部件的外殼。因在流體偶合中輸出速度小于輸入速度 ,其間的差值稱為滑差 ,一般為 1 %～ 3 %。偶合器的葉輪裝在 AC 電機(jī)上 ,渦輪裝在從動減速器高速軸上 ， 包含操作部件的軸箱安裝在驅(qū)動基座。這種驅(qū)動無論在機(jī)械 ,或在電氣上都是很復(fù)雜的 ， 其驅(qū)動系統(tǒng)成本中等。這種控制提供了合理的平滑加速度 ， 但其計算機(jī)控制系統(tǒng)很復(fù)雜。 VFC設(shè)備是一個電力電子控制器 ,首先 第 10 頁 把 AC 整流成 DC ， 然后利用逆變器 ， 再將 DC 轉(zhuǎn)換成頻率、電壓可控的 AC。 VFC 控制器可以容易地裝在小功率輸送機(jī)驅(qū)動上。 2 使用 IGBT的中性點(diǎn)箝位三電平逆變器 由于串聯(lián)器件電壓均分容易 ,器 件每次開關(guān)的 d v/ d t 低以及輸出端出色的諧波品質(zhì)，三電平電壓型逆變器在大功率傳動應(yīng)用中變得越來越流行。 2. 3kV逆變器每個開關(guān)只需要一個 HVIGBT[2,3]。例如 ， 當(dāng)開關(guān) S1U和 S2U閉合時， U 相處于狀態(tài) P(正母線電壓 ) ， 反之 ， 當(dāng)開關(guān) S3U和 S4U閉合時， U 相處于狀態(tài) N (負(fù)母線電壓 ) 。若對輸入諧波有更高的要求 ， 可以使用 24 脈沖二極管整流器作為輸入變流器。圖中指令磁通 Ψr 是速度的函數(shù) ,反饋速度和前饋滑差控制信號 ω sl相加。它以一種優(yōu)化方式確定每一次開關(guān)時刻 。圖 3為測試結(jié)果波形。在這些選擇中，可變頻率控制 (VFC)的方法顯現(xiàn)出在將來長距離輸送中帶式輸送機(jī)扮演了重要