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IJETT-V15P269

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   International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 7 – Sep 2014 ISSN: 2231-5381 http://www.ijettjournal.org  Page 360 Simulation of Three Phase Three Level Rectifier Achieved by NPC Phenomenon Samuel William 1  , MR. Sudheer S. Phulambrikar  2 , Mr. S.S.Thakur  3 1 PG Student & Electrical SATI VIDISHA(M.P.) 2  Assistant Professor Electrical Dptt SATI VIDISHA(M.P.) 3  Associated professor & HOD Electrical Dptt SATI VIDISHA(M.P.)    Abstract- A novel topology of a three phase three level Rectifier achieve by NPC phenomenon is presented in this paper. Switches control by pulse width modulation technique used. The implementation is by using NPC (Neutral point controlling) clamping. The input voltage is given to all three phases is 55 volt each and the output boost voltage we get up to 600volt. The final output is due to the two lower outputs at two capacitors and one common output (as we say three levels of rectifier). The voltage across these two capacitors (lower levels) is about 300volt. And hence we are getting a common output, at third level of 600volt   Key words- NPC (neutral point clamping), PWM (pulse width modulation). I.   INTRODUCTION Three phase analysis of the rectifier is not easily done but the analysis by this model analyze how the cascaded things work and how we BOOST the voltage with cascaded rectifiers. we use the switching by PWM method why which we take the action for generating the switching pulses for the IGBTs. Advantage of this rectifier is the less number of switches and diodes for achiving boost rectification with three leg. The topology as chosen here is the three level diode clamped rectifier and is also known as the Neutral point clamped rectifier or NPC rectifier. This is the structure which is first  proposed by Nabae et. Al. In 1980 the figure drawn bellow shows its topology. The  NPC topology , The DC voltage bus is split into 3 levels by using two DC capacitors, C1 and C2. Each capacitors is having Vdc/2 volts and each voltage stress will be limited to one capacitor level through the help of the clamping diodes. However , the line voltage Van presents three levels of the voltages. The main advantages of the NPC rectifiers is the reduced number of the levels and the semiconductors for a good  performance and also allow the low level EMI and THD. II. SIMULATION MODEL Figure 1 shows the SIMULATION MODEL of three phase  NPC rectifier. The model is three level model where the three  phase input is given and at the output we are getting a combined voltage of the two capacitors. The model is having three legs. Each of which is four switches. Here the switches we are using are IGBT’s. And there are three pair of diodes which are inserted in each of these legs. So each of the leg is having a combination of IGBT’s and diode’s, the combination of which is called as NPC.  NPC means neutral point clamping, which means to neutral the diode, in support of which the input is also neutral. And at the output side we have two capacitors. The output voltage of the capacitors together gives us the boosted voltage, which is higher than the input voltage. In this way we are getting output  boost voltage through three phase NPC rectifier. The figures, fig 2(a), 2(b) and fig 2(c) are the circuit that shows the valid operating phase modes of the NPC rectifier for different phases. there are three phases in which the rectifier worked Va=120 Vb= 0, and Vc=(-) 120   International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 7 – Sep 2014 ISSN: 2231-5381 http://www.ijettjournal.org  Page 361 Fig 1 Simulation MODEL of three phase NPC rectifier    Fig 2(a) Vin=(-)120 phase model Fig 2(b) Vin= 0 phase mode Fig 2(c) Vin= (+)120 phase mode   International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 7 – Sep 2014 ISSN: 2231-5381 http://www.ijettjournal.org  Page 362 III.   SWITCHING CONTROL Fig 3 input voltage and current characteristics Fig 4 switching characteristics IV.   SIMULATION RESULT The simulation results gives us the three level rectifier and its output result. The topology presented in this work gives the voltages Vo1 and Vo2. . The common output of both these voltages gives the result (Vo1+Vo2). . The current in the diode gives the different characteristics. . The simulation also gives the voltage difference (Vo1-Vo2). Fig 5 capacitor output voltage Vo1 Fig 6 capacitor output voltage Vo2 The figure above shown gives the output result for the NPC rectifier. These two figures, are giving the output of the two capacitors. The voltage provided to the input side is 150 volt. And the output voltages we are getting at the capacitor’s side are 300 volt each. The necessary condition is that both the capacitors should get this voltage to be same. And it is clear from these results that the output of these two capacitor is same, i.e. 300 volt each.   International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 7 – Sep 2014 ISSN: 2231-5381 http://www.ijettjournal.org  Page 363 Fig 7 The output voltage (Vo1+Vo2) Fig 8 output voltage (Vo1-Vo2) ã As it is clear from the results of simulation that the capacitors voltages we are getting is 300 volt each i.e. Vo1 (fig 5.1) and Vo2 (fig 5.2) each is 300 volts. And so as a result of implementation, the boost voltage, that is, our final dc voltage is 600 volts. And hence the addition of both the two lower levels (Vo1 and Vo2) gives us the third level (Vo1+Vo2)fig 5.4. So is called a three level rectifier. ã The voltages at capacitors are Vo1 and Vo2, and each is having a voltage of 300 volts. The above figure, show us the difference of both the voltages of the two capacitors Vo1 and Vo2. ã The voltage (Vo1-Vo2) is therefore approximately constant and having fluctuations of +100 to -100. The harmonics are smaller as compared to two level rectifiers. Conclusion Here by using the phenomenon of NPC and PWM technique, the three phase three level rectifier is achieved. And thus we have received our boost output voltage. The input voltage to the three  phases are given 165 volts and by getting the lower voltages from capacitors side the output boost voltage is of 600 volts. The lower level voltages at the two capacitors are 300 volts each. And the final output due to these two lower voltages is a boosted dc voltage of 600 volts. The sizes of the capacitors is quite large than those with the eight switches NPC converter to maintain the same voltage level. The dc bus voltage we are getting is 11 times more than the line voltage. Computer simulation results are presented to demonstrate the validity and effectiveness of the proposed control scheme.   References 1.   Prof Ned Mohan “ power electronics converter applications and degine” 2.   Trazyanadlowski, A. (1996). An overview of modern PWM techniques for three-phase, voltage-controlled, voltage source inverters. In  proceeding of the International sympostum industry electronics conferrence, warsaw, poland, 1996, 25-39. 3.   T. Sakkos, V. Sarv, and J. Soojärv, “Optimun Diode-Switched Active Filters for Power Factor Correction of Single- and Three- Phase Diode Recifiers with Capacitive Smoothing,” in Proc. of the 7th European Conf. on Power Electron. and Appl., Trondheim, Norway, Vol. 2, pp. 870-875, 1997. 4.   Holtz, j .(1996) pulsewidth modulation- A survey. IEEE Transaction on industrial electronics, 39, 6 (1996),410-420. 5.   Abdul Hamid Bhat and Pramod Agarwal “Improved Power Quality AC/DC Converters” National Institute of Technology Srinagar, Kashmir India 6.   B. Sirisha, N. Susheela, P. Satishkumar” Three Phase Two Leg Neutral Point Clamped Converter with output DC Voltage Regulation and Input Power Factor Correction” International Journal of Power Electronics and Drive System (IJPEDS) Vol.2, No.2, June 2012, pp. 138~150 ISSN: 2088-8694 7.   M.S. Djebbar , H. Benalla “AC/DC and DC/AC multilevel converter and dc voltage regulation . Applied to the asynchronous machine “ international conference o n petroleum and sustainable development IPCBEE 2011 vol 26 (2011 ) IACSIT Press singapore 8.   www.wikipedia.com 9.   Prof M. H. Rashid “ power electronics circuits devices and application”.
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