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Guide:Dr. Y R Manjunath
ChairmanElectrical Engg. Dept.
Batch Members:Chinmayi N S (11GAEE5016)
Ranjan T R (11GAEE5062)
Title: Multi level inverters using cascaded H-bridge.
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Power inverters convert electrical energy of DC form into that of AC.
It synthesizes the desired ac output waveform from several dc sources.
This project focuses on improving the efficiency of the multilevel inverter and quality of output voltage waveform.
A Seven level cascaded H-bridge inverter with reduced number of switches is implemented for the same.
Fundamental Switching scheme and Selective Harmonics Elimination will be implemented to reduce the Total Harmonics Distortion (THD).
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Introduction
The conventional technology used for inverters typically consists of either square-wave or pwm inverters. [1]
The square wave type is the simplest method to produce AC from DC.
However, it suffers from low frequency harmonics which causes difficulty in filtering out the noise to prevent these harmonics to return back to the primary side of the transformer.[2]
Literature survey
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The pwm inverter, forces the harmonics to be way up higher than the fundamental (line) frequency.
Thus, easing up the filtering requirement of the inverter.
However, the major drawback of the pwm inverter is the increased switching losses due to the frequent switching actions of the electronic switches.[3]
Literature survey(Cont’d)
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Literature survey(Cont’d) Multi-level inverter can avoid extra clamping diodes or voltage
balancing capacitors.[8][9] The converter topology used here is based on the series connection
of single phase inverters with separate DC sources. [10]
But it requires more number of switches.[11]
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Sl.no
Author name
Publisher Method Advantages/ Disadvantages
1. Samuel Muehleck
California Polytechnic State
University
Square wave type inverter
Noise, problems of filtering
2. Jim Doucette Dan Eggleston Jeremy Shaw
N E C A M S I D PWM inverters Very good sine output / Switching losses
3. Muhammad Ashraf Bin Zulkepple
Universiti Teknikal Malaysia Melaka
Sinusoidal Pulse Width
Modulation
Harmonics will increase the working frequency
4. Dr.K.Sathiyasekar
International Journal of
Engineering Trends and Technology
Interconnected H-Bridge Inverter
Less complex control ckt / More number of switches
5. Prof. Preeti V. Kapoor
Mamata N. Kokate
International Journal of Innovative
Research & Studies
Flying capacitor multilevel inverter
Balancing of capacitors is difficult
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AimThis project proposes an improved version of the H-bridge
inverter by increasing the number of steps per one period of the desired frequency with the use of electronic switches. This project aims at reduction of harmonic distortion with appropriate techniques.
Objectives The new topology has the added advantage of reduced number of
devices compared to conventional multi level inverter. It can be extended to any number of levels. No Electromagnetic Interference(EMI) and input current with low
distortion.
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Methodology: Previous method Analog PWM control requires
the generation reference and carrier signals that feed into a comparator.
The reference signal is sinusoidal.
When the carrier signal exceeds the reference, the comparator output signal is at one state, and when the reference is at a higher voltage, the output is at its second state.
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Disadvantages It uses the normal inverter that is VSI (but without the multilevel
part)so the power injection is done but the harmonics remain the same.
The regulation of the system is low. The overall efficiency of the circuit is less compared to the
proposed system.
9
An H-bridge converter is a switching configuration composed of four switches in an arrangement that resemble an ‘H’.
It is a compromise between a complicated, but high quality PWM inverter, and a simple, but low quality square wave inverter.
By controlling different switches in the bridge, positive, negative or zero potential voltage can be placed across a load.
Modes of operation. 1. Powering mode.2. Free wheeling mode.3. Regenerative mode.
.
Proposal of the new concept
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Selective Harmonics Elimination Stepped Waveform (SHESW) method will be used to eliminate the lower order harmonics.
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Fundamental switching scheme can be used to control the power electronic switches. Its corresponding Fourier series Equation is,
V (ωt) = ( 4Vdc/π) Σ [cos (n θ1)+ cos (n θ2) + ..+cos (n θs)] sin (nωt) where n = 1, 3, 5, 7, ...
The harmonic reduction is achieved by selecting appropriate switching angles given by,
cos ( θ1)+ cos ( θ2)+cos ( θ3)+cos ( θ4) = 3ma
cos(5θ1)+cos (5θ2)+cos(5θ3)+cos(5θ4) = 0
cos (7θ1)+cos (7θ2)+cos (7θ3)+cos (7θ4) = 0
where modulation index ma is given by ma=m/s, 0 ≤ ma ≤ 1 and m=V1/(4Vdc/π).
Here θ1, θ2, θ3, θ4 are the firing angles in degrees.
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Harmonic content decreases . Higher efficiency. The regulation of the inverter is good. Switching losses can be avoided. Reduction in number of switches. Applications: Power systems(substation, generating station and distribution
station). Reactive power compensator. Back to Back intertie. Utility compatible adjustable speed drives.
Advantages:
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The simulation for the proposed single phase and three phase inverters have been achieved successfully with both R-load and RL-load using Simulink software. The screenshots of the same have been shared here.
Single phase inv. Single phase output waveform
Update
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Simulation results (Cont’d) Three phase inv.
Three phase output waveform Firing circuit waveforms
15
The fundamental switching scheme with a microprocessor. Simple additions such as circuit protection and a closed loop
control could greatly improve the performance of this project. The conduction losses will be less, if number of switches is
reduced. The size of the multilevel inverter will be compact than other
inverters. The overall cost will be reduced by reducing the number of main
switches.
Conclusion:
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[1] “Power Electronics Circuits, Devices & Applications” , Muhammad H. Rashid, Third Edition, Prentice Hall India.
[2] “Design and Simulation of Interconnected H-Bridge Inverter”, Samuel Muehleck, California Polytechnic State University, San Luis Obispo, June, 2012.
[3] “DC/AC Pure Sine Wave Inverter”, Jim Doucette, Dan Eggleston, Jeremy Shaw, 2006-2007, NECAMSID, Worchester.
[4] “Linear Integrated Circuits”, D.Roy Choudary, Shail B.Jain, Second Edition, New Age International Publishers.
[5] “Power Electronic for Technology”, Ashfaq Ahmed, PEARSON Education.
[6] “Generalized structure of a multilevel PWM Inverter”, P.Bhagwat and V.R.Stefanovic, IEEE Trans. Ind. Appln, VoI.IA-19. no.6, pp. I OS7-1069, Nov-Dec .. 1983.
[7] “Multilevel Inverters; A Survey of Topologies, Controls, and Applications”, J.Rodriguez, Jih-sheng Lai, and F Zheng peng, IEEE Trans. Ind. Electron., vol.49 , n04., pp.724-738. Aug.2002.
[8] “Analysis and Simulation of New Seven Level Inverter Topology”, K.Surya Suresh and M.Vishnu Prasad, International Journal of Scientific and Research Publications, Volume 2, Issue 4, April 2012.
[9] “Single leg H-bridge inverters”, Prof. Preeti V. Kapoor Mamata N. Kokate, International Journal of Innovative Research & Studies, Vol 2 Issue 4.
[10] “Design and Implementation of Seven Level Cascaded H-Bridge Inverter Using Low frequency transformer with Single DC Source”, T. Singaravelu, M.Balasubramani, J.Gowrishankar, International Journal of Engineering and Technology.
[11] “New Modified Cascaded H-Bridge Multilevel Inverter Topology with Reduced Switches”, Dr.K.Sathiyasekar, International Journal of Engineering Trends and Technology, Volume 9 Number 4.
References:
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