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.

1

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).

2

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

3

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)

4

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]

5

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

6

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.

7

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.

8

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

10

Selective Harmonics Elimination Stepped Waveform (SHESW) method will be used to eliminate the lower order harmonics.

11

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.

12

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:

13

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

14

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:

16

[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:

17