International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 7 – Sep 2014
Simulation of Three Phase Three Level Rectifier
Achieved by NPC Phenomenon
Samuel William1 , MR. Sudheer S. Phulambrikar2, Mr. S.S.Thakur3
1
PG Student & Electrical SATI VIDISHA(M.P.)
Assistant Professor Electrical Dptt SATI VIDISHA(M.P.)
3
Associated professor & HOD Electrical Dptt SATI VIDISHA(M.P.)
2
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
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.
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
II. SIMULATION MODEL
common output (as we say three levels of rectifier). The voltage
Figure 1 shows the SIMULATION MODEL of three phase
across these two capacitors (lower levels) is about 300volt. And
NPC rectifier. The model is three level model where the three
hence we are getting a common output, at third level of 600volt
phase input is given and at the output we are getting a
Key words- NPC (neutral point clamping), PWM (pulse
width modulation).
I.
INTRODUCTION
three legs. Each of which is four switches.
Here the switches we are using are IGBT’s. And there are
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.
ISSN: 2231-5381
combined voltage of the two capacitors. The model is having
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
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Va=120 Vb= 0, and Vc=(-) 120
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International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 7 – Sep 2014
Fig 1 Simulation MODEL of three phase NPC rectifier
Fig 2(a) Vin=(-)120 phase model
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Fig 2(b) Vin= 0 phase mode
Fig 2(c) Vin= (+)120 phase mode
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International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 7 – Sep 2014
III.
. The common output of both these voltages gives the result
SWITCHING CONTROL
(Vo1+Vo2).
. The current in the diode gives the different characteristics.
. The simulation also gives the voltage difference (Vo1-Vo2).
Fig 3 input voltage and current characteristics
Fig 5 capacitor output voltage Vo1
Fig 6 capacitor output voltage Vo2
The figure above shown gives the output result for the NPC rectifier.
Fig 4 switching characteristics
These two figures, are giving the output of the two capacitors. The
IV.
SIMULATION RESULT
voltage provided to the input side is 150 volt. And the output voltages
The simulation results gives us the three level rectifier and its
we are getting at the capacitor’s side are 300 volt each. The necessary
output result.
condition is that both the capacitors should get this voltage to be
The topology presented in this work gives the voltages Vo1
same. And it is clear from these results that the output of these two
capacitor is same, i.e. 300 volt each.
and Vo2.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 15 Number 7 – Sep 2014
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.
Fig 7 The output voltage (Vo1+Vo2)
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Fig 8 output voltage (Vo1-Vo2)
•
As it is clear from the results of simulation that the
capacitors voltages we are getting is 300 volt each i.e. Vo1
7.
(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
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two lower levels (Vo1 and Vo2) gives us the third level
(Vo1+Vo2)fig 5.4. So is called a three level rectifier.
•
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.
•
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.
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