【正文】 ntrol system with NTC three. level inverters used in a 2. 7 km long belt conveyor drives in Chengzhuang Mine indicates that the performance of NPC threelevel inverter using HVTGBTs together with the control strategy of rotor fieldoriented vector control for induction motor drive is excellent for belt conveyor driving system. 。s impellers are mounted on the AC motor and the runners on the driven reducer highspeed shaft. Housing mounted to the drive base encloses the working circuit. The coupling39。 the driving hydraulic turbine known as the runner and a casing that encloses the two power ponents. Hydraulic fluid is pumped from the driven impeller to the driving runner, producing torque at the driven shaft. Because circulating hydraulic fluid produces the torque and speed, no mechanical connection is required between the driving and driver power produced by this coupling is based on the circulated fluid39。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,load sharing and variable speed are primary considerations. DC motors generally are used with higherpower conveyors, including plex profile conveyors 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。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 a ,the control systems for these can be highly plex, because they are 9 based on puter control of the resistance switching. Today, the majority of control systems are custom designed to meet a conveyor system39。 choices[1]. 1 Analysis on conveyor drive technologies 1. 1 Direct drives Fullvoltage starters. With a fullvoltage starter design, the conveyor head shaft is directcoupled to the motor through the gear drive. Direct fullvoltage starters are adequate for relatively lowpower, simple Profile conveyors. With direct fullvoltage starters. no control is provided for various conveyor loads and. depending on the ratio between full and noload power requirements, empty starting 8 times can be three or four times faster than full load. The maintenancefree starting system is simple, lowcost and very reliable. However, they cannot control starting torque and maximum stall torque。 performance. A efficient drive system should be able to provide smooth, soft starts while maintaining belt tensions within the specified safe limits. For load sharing on multiple drives. torque and speed control are also considerations in the drive system39。通過成莊煤礦 2. 7km 長帶式輸送機中采用的中點嵌位三電平逆變器變頻調速 (VFC)控制系統(tǒng)的測試結果表明，采用 BVIGBT 的中點嵌位三電平逆變器以及使用轉子磁場矢量控制策略的感應電機變頻傳動，使帶式輸送機驅動系統(tǒng)具有非常優(yōu)秀的性能，顯示出良好的應用前景。在這些選擇中，可變頻率控制 (VFC)的方法顯現出在將來長距離輸送中帶式輸送機扮 演了重要的角色。從圖中可以發(fā)現，帶張力的波動范圍很小，所有檢測結果顯示出帶式輸送機驅動系統(tǒng)令人滿意的特性。圖 3 為測試結果波形。作為一個附加的自由度，參考波與三角波的相對位置可改變，這可以用于直流環(huán)節(jié)6 中點的電流平衡。 產生的諧波盡可能的小，使用盡可能低的開關頻率以最小化開關損耗 。其基本原理是三電平 PWM 調制器使用兩個參考波認 Ur1 和 Ur2，但只使用一個三角波。對相加結果的頻率信號積分，然后產生單位矢量 (cosθ e 和 sinOθ e )，最后通過矢量旋轉器產生電壓 V’角θ控制 PWM 調制器。 逆變器控制 電機控制感應電機的控制可以使用轉子磁場定向矢量控制器實現，通過使用 PWM 調制器完成了恒轉矩區(qū)和高速弱磁區(qū)的控制。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。為了保證中性點電壓平衡，在 o 點被注入的平均電流應該是零 。例如，當開關 S1u 和S2u 閉合時， U 相處于狀態(tài) P(正母線電壓 )，反之，當開關 S3u 和 S4U 閉合時， U 相處于狀態(tài) n(負母線電壓 )。與兩電平電壓型逆變器相比，三電平中點箱位電壓型逆變器提供三個電