CAREER

EPISODE 2

v

Introduction

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.