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CAREEREPISODE vIntroduction CE1.1In this episode on the projecttitled ‘Simulation of Bidirectional Isolated DC-DC Converter for an EnergyStorage System, I am going to highlight my skills and technical abilitiescovered under my graduation. At that time, I was studying in Bachelors ofElectrical & Electronics Engineering from Aurora’s Engineering College,Hyderabad, India. There was one other teammate with me in the execution of thistechnical work activity.Title:Simulation of Bidirectional Isolated DC-DC Converter for an Energy StorageSystemDuration:month 20xx to month 20xxLocation:Hyderabad, IndiaPosition:Project Engineer (Electrical)vBackground CE1.2The converter has two symmetricalfull bridge converters. In the presence of DC supply power transfer to thesecond converter and charges the capacitor bank, when the power supply isabsent.

The converter operates in the reverse mode i.e. bridge 2 to bridge 1using storage device as a source. Inboth the modes (i.

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e. forward mode and reverse mode of operation) the powerswitches can be controlled by the pulse generators. The bidirectional Dc-DCconverter is involved in power flow between two DC sources. CE1.3 These two converter bridges allow power flowin both the directions without change in polarity of voltage. The proposedconverter can be analyzed for different frequencies.

Soft switching techniquecan be implemented to reduce the switching losses. I applied a number ofelectrical engineering concepts and techniques while designing the project andalso supervised the output as per the plan of the project design. Apart fromtechnical designing, I was also conscious regarding timeline and management ofsub-activities of project design.

CE1.4The main objective of thisproject was to store the energy in the energy storage system with an additionalfunction of galvanic isolation. I connected an energy storage device such as anelectric double layer capacitor directly to a DC side of the DC-DC converterwithout any chopper circuit. This project dealt with a bidirectional DC-DCconverter with a three phase rectifier circuit. I obtained bi-directional powerflow by a simple, efficient and galvanic ally isolated DC-DC converter.

Ianalyzed the charging and discharging operation of the proposed converter byMATLABSIMULINK.   CE1.5My position in the project isshown below: CE1.6 Mainresponsibilities I had in this project were:·     Introduced basic design of DC-DC converter bylooking its block diagram and modes of operation.·     Literature survey of the circuit design incontext to electrical design principles.

·     Theoretical analysis of the converter withcycle diagrams of modes of operations.·     Simulation model of the projected model withthe help of suitable simulation software.·     Performance analysis of the output followedby conclusion and future scope of improvements in the design.

Personal Engineering ActivityCE1.7When I was in the bachelor’sdegree program of JNTU, I submitted a technical thesis on this project forassessing my technical knowledge. Beginning of the project was with thesubmission of a brief synopsis on the technical points of the proposed project withthe description of the flow of work activities to be followed in order toachieve the final objective of the project.

It was a team task in which therewere two teammates and I performed as the leader of the team.CE1.8In the first phase of the project,I got introduced with DC-DC converters with the block diagrams of its two modesof operations. For this background study, I studied many textbooks and alsotook some help from the internet. I also explored working principle and partsof this converter with their main functions.

I accumulated data and informationafter referring to many books, articles and technical papers written bywell-known authors. After analyzing all these technical papers, I found that therewas a necessity to develop a high efficiency DC-DC converter for an energystorage system. CE1.9 I decided to improve the efficiency of thisconverter by adopting ZVS Technique Apart from improving efficiency of the converter;the converter was featured with equal voltages in the both the circuits to improvethe overall performance and the applications of this converter.

So, I implementedthe equal voltages in the both circuits with energy storage system with theexisting converter model. To construct the proposed converter, I made use of componentslike switches, pulse generators, transformer and auxiliary devices.CE1.10The main component I used in thisproject was Insulated Gate Bipolar Transistor (IGBT switch) in the convertersto convert power from AC to DC either DC to AC.

The new converter was based ona full bridge topology. In addition, I achieved unified ZVS in either directionof power flow without any additional component. Therefore, I used a minimumnumber of devices in the proposed circuit. Also the design had less control andaccessory power needed than its full-bridge competitors.CE1.11In the power supply unit, I madeuse of transformer, rectifier, filter & regulator.

I connected ACvoltage  of  typically 200V rms  to a  transformer, transformerchanged  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 frequencyinverters for dc-dc converter. In the energy storage system i.e. electricdouble layer capacitor or capacitor bank, I connected a number of capacitors inseries/parallel to store the energy.

CE1.12I noticed that in the proposedconverter circuit losses were present.    They were copper losses and Core losses in transformer, switching losses andconduction losses in the converters. I carried out many calculations for varyingswitching frequencies from 10 KHz to 30 KHz to get the values of losses. Itabulated the mathematical calculations for various switching frequencies from15 KHz to 30 KHz and found that as frequency of operation for converter wasincreasing the losses were also increasing. I executed simulations of thetechnical parameters as given below: CE1.13I made graphs between efficiencyand frequency in MS-Excel. I developed the simulation circuit of a normal dc-dcconverter and it was simulated for an input voltage of 350V.

The circuit diagramof DC-DC converter is shownI developed the simulation modelof dc-dc bidirectional converter by using MATLAB 7.9 Software package andSimulink toolbox.CE1.14I discussed about simulationmodels of forward and reverse mode results and compared these results withtheoretical results. Theoretical calculations of power losses and peak currentclarified the dc-voltage limitations in the energy storage system. Experimentalresults revealed that the dc-dc converter can charge the capacitor bank fromzero to the rated voltage without any external pre-charging circuit anddischarging the capacitor bank for continuous supply to the load.

In this way,my hard work proved successful as I obtained the results positively.v SummaryCE1.15In this project, I implementedZVS technique to decrease the losses .

The EDLC storing the energy up to 55V andwhenever supply was not present the capacitor bank was working as a source sothat the energy was flowing in the reverse direction which showed bidirectionalnature in the circuit. I learned many new technical concepts by completing thisproject and improved my skills of circuit design and analysis. I also enhancedmy software abilities in MATLAB and Solid Works.     

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