IJIRST –International Journal for Innovative Research in Science & Technology| Volume 3 | Issue 03 | August 2016
ISSN (online): 2349-6010
Multilevel Inverter with Reduced Number of
Switches using Multi Carrier Phase Opposition
Disposition PWM
Manu Jacob T
PG Scholar
Department of Electrical & Electronics Engineering
Federal Institute of Science and Technology Angamaly, India
Sreeja E A
Assistant Professor
Department of Electrical & Electronics Engineering
Federal Institute of Science and Technology Angamaly, India
Abstract
Multilevel inverter is one of the attractive topology for dc to ac conversion. Multilevel inverter synthesizes desired voltage wave
shape from several levels of DC voltages. Though multilevel inverter has a number of advantages it has drawbacks in the vein of
higher levels because of using more number of semiconductor switches. This may leads to vast size and price of the inverter
increases and also leads to complex control. The new multilevel inverter with reduced number of switches overcome this
problem and is well suited for high power applications. Multi carrier PWM technique is used for sine wave generation.
PODPWM with optimization of carrier using absolute sine reference signal is used for control.
Keywords: Multi Carrier Phase Opposition Disposition, PWM
_______________________________________________________________________________________________________
I.
INTRODUCTION
Power inverter is an electrical power device which is used to convert direct current (DC) into alternating current (AC). Using few
control circuits and switches, one can get AC at any required voltage and frequency. Inverter plays exactly the opposite role of
rectifiers as rectifiers are used for converting alternating current (AC) into direct current (DC).Multilevel inverters include an
array of power semiconductors and capacitor voltage sources, the output of which generate voltages with stepped waveforms.
The commutation of the switches permits the addition of the voltages, which reach high voltage at the output, while the power
semiconductors must withstand only reduced voltages. By increasing the number of levels in the inverter, the output voltages
have more steps generating a staircase waveform, which has a reduced harmonic distortion. Multilevel inverter is widely used in
high power applications such as large induction motor drives, UPS systems and Flexible AC transmission Systems. Desired
output can be obtained from several levels of input DC voltage sources and also the output levels depends on the number of input
DC voltage sources. The multilevel inverters o_er several advantages over a conventional two level inverters such as lower
semiconductor voltage stress, better harmonic performance, low Electro Magnetic Interference (EMI) and lower switching
losses. The main drawback in Conventional cascaded multilevel inverter is that when levels are increasing it requires more
number of semiconductor switches. This increases the inverter size and makes the control scheme more complex. Multilevel
inverter with reduced number of switches reduces inverter size and makes the control less complex. The Diode clamped, Flying
capacitor, Cascaded H-bridge inverter are the three main different multilevel inverter structures which are used in industrial
applications with separate dc sources. In flying capacitor and diode-clamped inverter there is a problem of capacitor voltage
balancing and this problem is overcome in cascaded H-bridge inverter. Conventional cascaded seven level multilevel inverter
require twelve switches and three dc sources separately. The main drawback in Conventional cascaded is that when levels are
increasing it requires more number of semiconductor switches. As a result some alternations are to be made inorder to reduce the
size and switch of the inverter
II. NOVEL MULTILEVEL INVERTER WITH REDUCED NUMBER OF SWITCHES
The novel topology of multilevel inverter with reduced number of switches can be used for different levels of output. The
number of output voltage levels changes with number of switches and DC sources. The generalized expression for the number of
𝑛+1
switches is given by and the number of dc sources for the proposed topology is given by 𝑣 =
Where N= number of levels
2
and V= number of switches. The generalized expression for the number of dc sources is given by s =
voltage sources.
𝑛+5
2
Where S=number of dc
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Multilevel Inverter with Reduced Number of Switches using Multi Carrier Phase Opposition Disposition PWM
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III. SEVEN LEVEL INVERTER WITH SIX SWITCHES AND THREE DC SOURCES
The figure 1 shows the novel seven level inverter topology with three dc sources and six switches. It is simple in design
compared to the existing topologies. It also have additional features like only two switches conducting at an interval of time.
Two switches used for polarity reversal and the remaining four switches used for waveform generation.
Fig. 1: Novel seven level inverter
Figure 1 shows the circuit arrangement of novel topology of seven level inverter which consists of six switches and the
resistive load is used. Switches S4 and S6 are used for reversal polarity and the remaining switches are used to generate the
levels in both positive and negative sides to produce the desired seven level waveforms. The switching states are given in the
table 1.
Table – 1
Switching states of novel seven level inverter
IV. NINE LEVEL INVERTER WITH SEVEN SWITCHES AND FOUR DC SOURCES
The figure 2 shows the novel nine level inverter topology with four dc sources and seven switches. It is simple in design
compared to the existing topologies. It also have additional features like only two switches conducting at an interval of time.
Two switches used for polarity reversal and the remaining five switches used for waveform generation. Figure 2 shows the
circuit arrangement of novel topology of nine level inverter which consists of seven switches, four DC sources and the resistive
load. Switches S6 and S7 are used for reversal polarity and the remaining switches are used to generate the levels in both positive
and negative sides to produce the desired seven level waveforms. The switching states are given in the table 2.
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Multilevel Inverter with Reduced Number of Switches using Multi Carrier Phase Opposition Disposition PWM
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Fig. 2: Novel nine level inverter
Table – 2
Switching states of novel nine level inverter
PODPWM Control with Carrier Optimization
Phase Opposition Disposition (Pod) pulse width modulation is employed for control of switches. With the PODPWM method the carrier
waveforms above the zero reference value are in phase. Using multi carrier phase opposition disposition pulse width modulation, seven level
inverter requires six carriers to be compared with sinusoidal reference signal and nine level inverter requires eight triangular carrier waves to be
compared with sinusoidal reference signal. The optimization of multi carrier phase opposition disposition PWM is done by taking the absolute
or positive value of the modulating reference sine wave. This method of optimization of PODPWM using absolute sine reference wave reduces
the number of carriers to half as shown in figure 3.
Fig. 3: Optimized PODPWM
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Multilevel Inverter with Reduced Number of Switches using Multi Carrier Phase Opposition Disposition PWM
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Number of carriers required for n level =
Modulation index M =
𝐴𝑟𝑒𝑓
𝑛−1
∗𝐴𝑡𝑟𝑖
2
𝑛−1
2
Atri is the amplitude of triangular wave, n is the number of levels of inverter. By optimization the number of triangular carriers required for
seven level inverter reduces to three and the number of triangular carriers required for nine level inverter reduces to four.
V. SIMULATION STRATEGY AND RESULTS
The novel topology of seven level inverter consists of six switches and three DC sources. The figure 4 shows simulation circuit diagram of
novel seven level inverter with seven switches and four DC sources.
Fig. 4: Simulation Circuit
The figure 5 shows the output of the nine level inverter with four DC Sources of 6 V and seven switches. The simulation results shows the
nine levels of the output voltage. The THD is obtained as4.58 % by FFT analysis in simulation and is shown in the figure 6.
Fig. 5: Output Voltage across Load
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Multilevel Inverter with Reduced Number of Switches using Multi Carrier Phase Opposition Disposition PWM
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Fig. 6: Total Harmonic Distortion
VI. CONCLUSION
A new topology for seven level multilevel inverter and nine level inverter is designed and the simulations are done in Matlab/Simulink for nine
level inverter. The simulation results across the load with nine levels are obtained. THD is obtained as 4.58 %. Optimized phase opposition
disposition pulse width modulation is used. Number of carriers required reduced to half.
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