【導(dǎo)讀】在運送大量的物料時，帶式輸送機在長距離的運輸中起到了非常重要的競爭作用。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)需耍給輸送帶?？刂乞?qū)動力和加速度扭矩是輸送機的關(guān)鍵。為了負載分配在多個驅(qū)動上，扭矩和速度控制在驅(qū)動系統(tǒng)的設(shè)計中也是很重要的因。由于輸送機驅(qū)動系統(tǒng)控制技術(shù)的進步，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。但是，不能控制啟動扭矩和最大停止扭矩。壓的SCR2鎖定在全導(dǎo)通，為電機提供全壓。在傳送裝置啟動時，把電阻串聯(lián)進轉(zhuǎn)子產(chǎn)生較低的。轉(zhuǎn)矩，當(dāng)傳送帶加速時，電阻逐漸減少保持穩(wěn)定增加轉(zhuǎn)矩。DC驅(qū)動技術(shù)一般應(yīng)用SCR裝置，它允許連續(xù)的變速操作。生的動力決定于液力偶合器的充液量，扭矩正比于輸入速度。須監(jiān)測AC電機電流給電磁閥的控制提供反饋。以滿足中高壓交流傳動應(yīng)用的需要。與兩電平電壓型逆變器相比，三電平中點箱位電壓

　　

【正文】 en either S3u, conducts depending on positive or negative phase current polarity, respectively. For neutral point voltage balancing, the average current injected at 0 should be zero. 2. 2 Line side converter For standard applications. a 12pulse diode rectifier feeds the divided DClink capacitor. This topology introduces low harmonics on. the line side. For even higher requirements a 24pulse diode rectifier can be used as an input converter. For more advanced applications where regeneration. capability is necessary, an active front. end converter can replace the diode rectifier, using the same structure as the inverter. 2. 3 Inverter control Motor Control. Motor control of induction machinesis realized by using a rotor flux. oriented vector controller. Fig. 2 shows the block diagram of indirect vector controlled drive that incorporates both constant torque and high speed fieldweakening regions where the PW M modulator was used. In this figure, the mand generated as function of speed. The feedback speed is added with the feed 15 forward slip mand signalψ,the resulting frequency signal is integrated and then the unit vector signals(cosθe and sinθ e)are generated. The vector rotator generates the voltage Vs and Angle θe mands for the PW M as shown. PWM Modulator. The demanded voltage vector is generated using an elaborate PWM modulator. The modulator extends the concepts of spacevector modulation 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 thusswitching losses are minimized. A in a twolevel inverter, a zerosequenceponent 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 16 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 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.