外文翻譯---帶式輸送機(jī)及其牽引系統(tǒng)(參考版)
2025-05-17 09:52本頁(yè)面
【正文】 P N and 0 are the do bus points. The phase U, for example, is in state P (positive bus voltage)when the switches S1uand S2u are closed, whereas it is in state N (negative bus voltage) when the switches S3u and S4u, are closed. At neutral point clamping, the phase is in 0 state when 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 machines is 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 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 14 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 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 co
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