CAREER · Theoretical analysis of the converter with cycle

CAREER
EPISODE 2

v
Introduction

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CE 2.1

In this episode on the project
titled ‘Simulation of Bidirectional
Isolated DC-DC Converter for an Energy Storage System’, I am going to
highlight my skills and technical abilities covered under my graduation, during
my study of Bachelors of Electrical & Electronics Engineering at Jawaharlal Nehru Technological University.

There was one other teammate with me in the execution of this technical work
activity.

Title:
Simulation of Bidirectional Isolated DC-DC Converter for an Energy Storage
System

Location:
Hyderabad, India

Position:
Project Engineer (Electrical)

 

v Background

 

CE 2.2

The converter has two symmetrical
full bridge converters. In the presence of DC supply power transfer to the
second converter and charges the capacitor bank, when the power supply is
absent. The converter operates in the reverse mode i.e. bridge 2 to bridge 1
using storage device as a source. In
both the modes (i.e. forward mode and reverse mode of operation) the power
switches can be controlled by the pulse generators. The bidirectional Dc-DC
converter is involved in power flow between two DC sources.

CE 2.3

 These two converter bridges allow power flow
in both the directions without change in polarity of voltage. The proposed
converter can be analyzed for different frequencies. Soft switching technique
can be implemented to reduce the switching losses. I applied a number of
electrical engineering concepts and techniques while designing the project and
also supervised the output as per the plan of the project design. Apart from
technical designing, I was also conscious regarding timeline and management of
sub-activities of project design.

CE 2.4

The main objective of this
project was to store the energy in the energy storage system with an additional
function of galvanic isolation. I connected an energy storage device such as an
electric double layer capacitor directly to a DC side of the DC-DC converter
without any chopper circuit. This project dealt with a bidirectional DC-DC
converter with a three-phase rectifier circuit. I obtained bi-directional power
flow by a simple, efficient and galvanic ally isolated DC-DC converter. I
analyzed the charging and discharging operation of the proposed converter by
MATLABSIMULINK.  

CE 2.5

My position in the project is
shown below:

 

CE 2.6

Main
responsibilities I had in this project were:

·     
Introduced basic design of DC-DC converter by
looking its block diagram and modes of operation.

·     
Literature survey of the circuit design in
context to electrical design principles.

·     
Theoretical analysis of the converter with
cycle diagrams of modes of operations.

·     
Simulation model of the projected model with
the help of suitable simulation software.

·     
Performance analysis of the output followed
by conclusion and future scope of improvements in the design.

Personal Engineering Activity

CE 2.7

When I was in the bachelor’s
degree program of JNTU, I submitted a technical thesis on this project for
assessing my technical knowledge. Beginning of the project was with the
submission of a brief synopsis on the technical points of the proposed project with
the description of the flow of work activities to be followed in order to
achieve the final objective of the project. It was a team task in which there
were two teammates and I performed as the leader of the team.

CE 2.8

In the first phase of the
project, I got introduced with DC-DC converters with the block diagrams of its
two modes of operations. For this background study, I studied many textbooks
and also took some help from the internet. I also explored working principle
and parts of this converter with their main functions. I accumulated data and
information after referring to many books, articles and technical papers
written by well-known authors. After analyzing all these technical papers, I
found that there was a necessity to develop a high efficiency DC-DC converter
for an energy storage system.

CE 2.9

 I decided to improve the efficiency of this
converter by adopting ZVS Technique Apart from improving efficiency of the converter;
the converter was featured with equal voltages in the both the circuits to improve
the overall performance and the applications of this converter. So, I implemented
the equal voltages in the both circuits with energy storage system with the
existing converter model. To construct the proposed converter, I made use of
components like switches, pulse generators, transformer and auxiliary devices.

CE 2.10

The main component I used in this
project was Insulated Gate Bipolar Transistor (IGBT switch) in the converters
to convert power from AC to DC either DC to AC. The new converter was based on
a full bridge topology. In addition, I achieved unified ZVS in either direction
of power flow without any additional component. Therefore, I used a minimum
number of devices in the proposed circuit. Also the design had less control and
accessory power needed than its full-bridge competitors.

CE 2.11

In the power supply unit, I made
use of transformer, rectifier, filter & regulator. I connected AC voltage
of  typically 200V rms  to 
a  transformer, transformer
changed  to  the desired ac voltage .A  IGBT 
rectifier  that  provided 
the  full wave  rectified 
voltage  that  was initially filtered  by 
a  simple  capacitor 
filter  to  produce a dc voltage. This resulting  dc  voltage  usually 
had  some  ripple 
or  ac  voltage 
variation. I used High switching frequency inverters for dc-dc converter. In the energy storage system i.e. electric
double layer capacitor or capacitor bank, I connected a number of capacitors in
series/parallel to store the energy.

CE 2.12

I noticed that in the proposed
converter circuit losses were present.   
They were copper losses and Core losses in transformer, switching losses and
conduction losses in the converters. I carried out many calculations for varying
switching frequencies from 10 KHz to 30 KHz to get the values of losses. I
tabulated the mathematical calculations for various switching frequencies from
15 KHz to 30 KHz and found that as frequency of operation for converter was
increasing the losses were also increasing. I executed simulations of the
technical parameters as given below:

 

CE 2.13

I made graphs between efficiency
and frequency in MS-Excel. I developed the simulation circuit of a normal dc-dc
converter and it was simulated for an input voltage of 350V.The circuit diagram
of DC-DC converter is shown

I developed the simulation model
of dc-dc bidirectional converter by using MATLAB 7.9 Software package and
Simulink toolbox.

CE 2.14

I discussed about simulation
models of forward and reverse mode results and compared these results with
theoretical results. Theoretical calculations of power losses and peak current
clarified the dc-voltage limitations in the energy storage system. Experimental
results revealed that the dc-dc converter can charge the capacitor bank from
zero to the rated voltage without any external pre-charging circuit and
discharging the capacitor bank for continuous supply to the load. In this way,
my hard work proved successful as I obtained the results positively.

v Summary

CE 2.15

In this project, I implemented
ZVS technique to decrease the losses .The EDLC storing the energy up to 55V and
whenever supply was not present the capacitor bank was working as a source so
that the energy was flowing in the reverse direction, which showed bidirectional
nature in the circuit. I learned many new technical concepts by completing this
project and improved my skills of circuit design and analysis. I also enhanced
my software abilities in MATLAB and Solid Works.

 

 

 

 

 

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