外文翻譯---帶式輸送機(jī)及其牽引系統(tǒng)-全文預(yù)覽
【正文】 ulation to the threelevel inverter. The operation can be explained by starting from a regularly sampled sinetriangle parison from twolevel inverter. Instead of using one set of reference waveforms and one triangle defining the switching frequency, threelevel Modulator uses two sets of reference waveforms Uand U and just one triangle. Thus, each switching transition is used in an optimal way so that several objectives are reached at the same time. Very low harmonics are generated. The switching frequency is low and thus switching losses are minimized. As in a twolevel inverter, a zerosequence ponent can be added to each set of reference waveform s in order to maximize the fundamental voltage ponent. As an additional degree of freedom, the position of the reference waveform s within the triangle can be changed. This can be used for current balance in the two halves of the DClink. 3 Testing results After Successful installation of three 750 kW /2. 3 kV threelevel inverters for one 2. 7 km long belt conveyor driving system in Cheng zhuang Mine. The performance of the whole VFC system was tested. Fig. 3 is taken from the test, which shows the excellent characteristic of the belt conveyor driving system with VFC controller. Fig. 3 includes four curves. The curve 1 shows the belt tension . From the curve it can be find that the fluctuation range of the belt tension is very small. Curve 2 and curve 3 indicate current and torque separately. Curve 4 shows the velocity of the controlled belt. The belt velocity have the s shape characteristic. All the results of the test show a 15 very satisfied characteristic for belt driving system. 4 Conclusions Advances in conveyor drive control technology in recent years have resulted in many more reliable. Costeffective and performancedriven conveyor drive system choices for these choices,theVariable frequency control (VFC) method shows promising use in the future for long distance belt conveyor drives due to its excellent performances. The NPC threelevel inverter using high voltage TGBTs make the Variable frequency control in medium voltage applications bee much more simple because the inverter itself can provide the medium voltage needed at the motor terminals, thus eliminating the stepup transformer in most applications in the past. The testing results taken from the VFC control 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。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。 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 contro
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