international islamic university chittagong

PI CONTROLLED BI-DIRECTIONAL DC-DC CONVERTER AND HIGLY EFFICIENT BOOST CONVERTER FOR ELECTRIC VEHICLE

BY REMON DAS & ASHRAF UDDIN CHOWDHURY

THESIS SUBMITTED IN FULFILLMENT OF THE REQUIREMENT FOR THE DEGREE OF BACHELOR OF SCIENCE (B. SC.) IN ELECTRICAL & ELECTRONIC ENGINEERING

Department of Electrical & Electronic Engineering

INTERNATIONAL ISLAMIC UNIVERSITY CHITTAGONG June 2014

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RECOMMENDATION This is to certify that Md Ashraf Uddin Chowdhury (ET 101015) & Remon Das (ET 101045), student of International Islamic University Chittagong under the department of Electrical & Electronic Engineering has carried out the thesis on titled “PI Controlled BI Directional DC DC Converter & Highly Efficient Boost Converter for Electric Vehicle” successfully under my supervision and guidance. To the best of my knowledge, the matter embodied in the thesis has not been submitted to any other university/Institute for the award of any Degree or Diploma.

Signature of the supervisor

---------------------------------------------------Md. Mizanur Rahman June 2017

Lecturer Dept. of EEE, IIUC

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CANDIDATES DECLARATION

It is hereby declare that the work have been done by us under the supervision of Engr. Mizanur Rahman , Lecturer, Department of Electronic Engineering, IIUC. The report or all the part related to this thesis is genuine. The thesis has not been published anywhere in full, or in a part. All items and sub items that appear on the thesis are referenced, where needed. The thesis cannot be copied from anywhere.

Signature of the Candidates

________________________ Md. Ashraf Uddin Chowdhury. ET-101015 ________________________ Remon Das. ET-101045

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ACKNOWLEDGEMENT

Firstly we express our gratefulness to almighty God as we have completed our dissertation successfully by His mercy. For this thesis paper, we would like to express our endless gratitude to our project supervisor Engr. Md Mizanur Rahman for his enormous support and careful guidance. Without his guidance it was almost impossible to carry out with the thesis work. He had been very helpful and ever affectionate to endure the mistakes we had committed in the thesis and always encouraged us by correcting our wrong proceedings. This thesis was not an easy one to carry on because of the unavailability of the theoretical materials. It is only the endless support offered by him that enabled us to complete this mammoth task. We would also like to thank all the teachers of the department of Electrical & Electronics Engineering of International Islamic University Chittagong for their day to day counseling, mentoring and sharing their experience, which made us progressive and enlightened. They were always been our mentors to show us right way and their suggestions and technical help was the blessings for our thesis work. Thanks all of your guidance and patronage.

Author Md. Ashraf Uddin Chowdhury & Remon Das.

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ABSTRACT Due to the constraint of the fuel the electric vehicle is designed for the modern world. Bidirectional DC to DC converters has significantly enlarged the interest in Electric vehicle applications. The present work aims at designing and modeling of a bidirectional DC to DC converter for driving a DC motor for Electric Vehicle (EV) application. In a conventional bi directional converter PWM (Pulse width modulation) pulse is used for the generation of triggering pulse of the switches. We use PI and PID controller for triggering the IGBTs of DC to DC converter. A comparison is done between the three types of bidirectional dc to dc converter. Then we also design a boost converter over conventional boost converter by using parallel combinations of IGBT and MOSFET for electric vehicle applications. After that we simulate the two mode of electric vehicle. First one is motoring mode and other one is regenerating mode. During motoring operation the bidirectional DC to DC converter operates in the step up mode (boost mode) to provide the energy from the battery to the traction motor while during regeneration the motor acts as a generator and the bidirectional DC to DC converter operates in step down mode (buck mode) to recharge the battery.

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TABLE OF CONTENTS

CHAPTER: 1 .................................................................................................................................. 1 INTRODUCTION .......................................................................................................................... 1 1.1 Background ........................................................................................................................... 1 1.2 Motivation ............................................................................................................................. 1 1.3 Contribution of the Thesis ..................................................................................................... 1 1.4 Literature Review .................................................................................................................. 2 1.5 Methodology We Will Use ................................................................................................... 3 1.5.1 PI controller for Bidirectional DC to DC Converter ...................................................... 3 1.5.2 Idea of designing Boost Converter by using IGBT & MOSFET combination .............. 3 1.5.3 Implementation of the System ........................................................................................ 3 1.6 Software ................................................................................................................................ 4 1.7 Organization of the Thesis .................................................................................................... 4 CHAPTER: 2 .................................................................................................................................. 5 MODELING OF BIDIRECTIONAL DC TO DC CONVERTER ................................................. 5 2.1 MODELING OF BIDIRECTIONAL DC TO DC CONVERTER (CONVENTIONAL) .... 5 2.1.1 DC to DC converter ........................................................................................................ 5 2.1.2 Bidirectional DC to DC converter .................................................................................. 5 2.1.3 Bidirectional DC to DC converters design for the Electric Vehicle ............................... 6 2.1.4 Classification of Bidirectional DC to DC converter ....................................................... 6 2.1.5 Steps of Designing an Isolated Bidirectional DC to DC converter (Conventional) ....... 6 2.1.6 Bidirectional DC to DC converter operation (conventional) .......................................... 8 2.2 SIMUATION AND RESULT ............................................................................................... 8 2.2.1 Mode of Bidirectional Converter .................................................................................... 8 2.2.2 Circuit Diagram for Boost Operation ............................................................................. 9 2.2.3 Simulation output ........................................................................................................... 9 2.2.4 Circuit Diagram for Buck Operation ............................................................................ 11 2.2.5 Simulation Output......................................................................................................... 11 2.2.6 Data table for different output voltage for the corresponding input voltage ................ 14 2.3 MODELING OF PI CONTROLLED HIGH EFFICIENT BIDIRECTIONAL DC TO DC CONVERTER .................................................................................................................... 14 2.3.1 Proportional and Integral Control (PI Control) ............................................................ 14 6|Page

2.3.2 Advantages of the PI Controller ................................................................................... 14 2.3.3 PI Control Strategy ....................................................................................................... 15 2.3.4 Steps of Designing an PI Controlled Bidirectional DC to DC converter ..................... 15 2.3.5 PI controlled Bidirectional DC to DC converter operation: ......................................... 17 2.4 SIMUATION AND RESULT ............................................................................................. 17 2.4.1 PI Control Circuit ......................................................................................................... 17 2.4.2 Circuit Diagram for Boost Operation ........................................................................... 18 2.4.3 Simulation Output......................................................................................................... 18 2.4.4 Circuit Diagram for Buck Operation ............................................................................ 20 2.4.5 Simulation Output......................................................................................................... 21 2.4.6 Data table for different output voltage for the corresponding input voltage ................ 23 2.5 MODELING OF PID CONTROLLED BIDIRECTIONAL DC TO DC CONVERTER .. 23 2.5.1 Proportional-integral-derivative controller (PID controller) ........................................ 23 2.5.2 Limitations of PID control ............................................................................................ 23 2.6 SIMUATION AND RESULT ............................................................................................. 24 2.6.1 PID Control Circuit ...................................................................................................... 24 2.6.2 PID controlled Bidirectional DC to DC converter operation ....................................... 24 2.6.3 Circuit Diagram for Boost Operation ........................................................................... 25 2.6.4 Simulation Output......................................................................................................... 25 2.6.5 Circuit Diagram for Buck Operation ............................................................................ 27 2.6.6 Simulation Output......................................................................................................... 28 2.6.7 Data table for different output voltage for the corresponding input voltage ................ 30 2.7 COMPARISON BETWEEN CONVENTIONAL, PI CONTROLLED AND PID CONTROLLED BI-DIRECTIONAL DC TO DC CONVERTER........................................... 30 CHAPTER: 3 ................................................................................................................................ 32 MODELLING OF BOOST CONVERTER.................................................................................. 32 3.1 MODELLING OF BOOST CONVERTER (CONVENTIONAL) ..................................... 32 3.1.1 BOOST converter (Step Up converter) ........................................................................ 32 3.1.2 Operating principle ....................................................................................................... 32 3.2 SIMUATION AND RESULT ............................................................................................. 33 3.2.1 Circuit Diagram of Boost Converter (conventional) .................................................... 34 3.2.2 Simulation Output......................................................................................................... 34 3.2.3 Data table for different output voltage for the corresponding input voltage ................ 36

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3.3 MODELLING OF BOOST CONVERTER BY COMBINATION OF MOSFET AND IGBT.......................................................................................................................................... 37 3.3.1 Parallel operation of IGBT and MOSFET .................................................................... 37 3.3.2 Advantages ................................................................................................................... 37 3.4 SIMUATION AND RESULT ............................................................................................. 38 3.4.1 Circuit Diagram of Boost Converter by combination of MOSFET and IGBT ............ 38 3.4.2 Simulation Output......................................................................................................... 38 3.4.3 Data table for different output voltage for the corresponding input voltage ................ 40 3.5 COMPARISON BETWEEN CONVENTIONAL BOOST CONVERTER AND BOOST CONVERTER BY COMBINATION OF MOSFET& IGBT .................................... 41 CHAPTER: 4 ................................................................................................................................ 42 BATTERY DISCHARGING MODE (NORMAL OR MOTORING OPERATION) ................. 42 4.1 Introduction ......................................................................................................................... 42 4.2 Block Diagram .................................................................................................................... 42 4.3 Circuit Diagram of motoring operation ............................................................................... 42 4.4 Circuit Operation ................................................................................................................. 42 4.5 SIMUATION AND RESULT ............................................................................................. 43 4.5.1 Simulation Output......................................................................................................... 44 4.5.2 Motor Characteristics ................................................................................................... 45 CHAPTER: 5 ................................................................................................................................ 47 Battery Charging Mode (Regenerating Operation) ....................................................................... 47 5.1 Introduction ......................................................................................................................... 47 5.2 Block Diagram .................................................................................................................... 47 5.3 Circuit Diagram of Regenerating Operation ....................................................................... 47 5.4 Regenerative breaking and Motor- Generator Operation (Circuit operation) ..................... 48 5.5 SIMUATION AND RESULT ............................................................................................. 48 5.5.1 Simulation Output......................................................................................................... 49 5.5.2 Generator Characteristics ............................................................................................. 50 5.5.3 Battery Characteristics .................................................................................................. 51 CHAPTER: 6 ................................................................................................................................ 53 CONCLUSION ............................................................................................................................. 53 6.1 Summery ............................................................................................................................. 53 6.2 Future work ......................................................................................................................... 53

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LIST OF FIGURES Figure 1.1: Battery Discharging Mode (Normal or Motoring Operation)………………..…...1 Figure 1.2: Battery Charging Mode (Regenerating Operation)..………………………...…....2 Figure 1.3: Combination of IGBT & MOSFET switch for Boost converter…………...…......3 Figure 2.1: A Block diagram of a bidirectional DC- DC converter………………….….…….5 Figure 2.2: A Block diagram of an isolated bidirectional DC- DC converter…………..…..…6 Figure 2.3: Inverter (Converter DC to AC)……………………………………………….…...7 Figure 2.4: Inverter cascaded with transformer………………………………………………..7 Figure 2.5: Bidirectional DC to DC converter (Conventional)………………………….….…8 Figure 2.6: Bidirectional DC to Dc converter without PI controller (Boost mood)…….….…9 Figure 2.6.1: Input Curve……………………………………………………….….…9 Figure 2.6.2: Inverter output Curve (transformer primary Voltage)…………………10 Figure 2.6.3: Transformer secondary Voltage…………………………….……....…10 Figure 2.6.4: Output Voltage of DC to DC converter……………………………..…11 Figure 2.7: Bidirectional DC to Dc converter without PI controller (Buck mood)……..……11 Figure 2.7.1: Input Curve………………………………………………………….....12 Figure 2.7.2: Transformer primary Voltage…………………………………..…..….12 Figure 2.7.3: Transformer secondary Voltage………………………………………..13 Figure 2.7.4: Output Voltage of DC to DC converter………………………………..13 Figure 2.8: Block diagram of PI control Strategy……………………………………….…...15 Figure 2.9: Inverter (DC to AC)………….…………………………………………….…….15 Figure 2.10: Inverter cascade with Transformer……………………………………..………16 Figure 2.11: Bidirectional DC to DC converter circuit without control circuit……..……….16 Figure 2.12: PI controlled Bidirectional DC to DC converter……………………………….17 Figure 2.13: PI Control Circuit……………………………………………………………….17 Figure 2.14: Bidirectional DC to Dc converter with PI controller (Boost mood)……………18 Figure 2.14.1: Input Curve…………………………………………………………...18 9|Page

Figure 2.14.2: - Transformer primary side output at boost condition…………...…..19 Figure 2.14.3: - Transformer secondary side output at boost condition………..……19 Figure 2.14.4: Output Curve…………………………………………………..…….20 Figure 2.15: Bidirectional DC to Dc converter with PI controller (Buck mood)…………….20 Figure 2.15.1: Input Curve………………………………………………..……….…21 Figure 2.15.2: - Transformer primary side output at buck condition…….………….21 Figure 2.15.3: - Transformer primary side output at buck condition………………..22 Figure 2.15.4: Output Curve………………………………………………..…….….22 Figure 2.16: PID Control Circuit…………………………………………………………….24 Figure 2.17: Bidirectional DC to Dc converter with PID controller (Boost mood)………….25 Figure 2.17.1: Input Curve………………………………………………………...…25 Figure 2.17.2: Transformer primary side output at boost condition………….……..26 Figure 2.17.3: Transformer secondary side output at boost condition………….…..26 Figure 2.17.4: Output Curve…………………………………………………………27 Figure 2.18: Bidirectional DC to Dc converter with PID controller (Buck mood)…………..27 Figure 2.18.1: Input Curve……………………………………………………….…..28 Figure 2.18.2: - Transformer primary side output at buck condition………………...28 Figure 2.18.3: - Transformer primary side output at buck condition………….…..…29 Figure 2.18.4: Output Curve………………………………………………….….…..29 Figure 3.1: A Block diagram of a boost converter……………………………………….…..32 Figure 3.1.1: When switch is closed………………………………………………….33 Figure 3.1.1: When switch is open…………………………………………..….……33 Figure3.2: Circuit diagram of boost converter (Conventional)………………………………34 Figure3.2.1: Input Voltage Curve……………………………………………..……..34 Figure3.2.2: Input current Curve……………………………………………..….…...35 Figure3.2.3: Output current Curve……………………………..…………………….35 Figure3.2.4: Output Voltage Curve……………………………………….………….36 10 | P a g e

Figure 3.3: Parallel Connection of IGBT and MOSFET…………………………………….37 Figure 3.4: Circuit diagram of boost converter (Combination)………………………………38 Figure 3.4.1: Input Voltage Curve……………………………………..…………….38 Figure 3.4.2: Input current Curve………………………………….…………………39 Figure 3.4.3: Output current Curve…………………………………..…….………...39 Figure 3.4.4: Output Voltage Curve………………………………………………….40 Figure 3.5: Comparison between Conventional & Combined IGBT-MOSFET switch Boost converter…………………………………………………………………………………...…41 Figure 4.1: Battery Discharging Mode (Normal or Motoring Operation)………………..….42 Figure 4.2: Battery discharging circuit of Electric Vehicle…………………………………..42 Figure 4.3: Circuit diagram with measuring scope……………………………………..……43 Figure 4.3.1: Input Voltage Curve……………………………………………………44 Figure 4.3.2: Output Curve during motor load……………………………………….44 Figure 4.3.3: Speed Curve………………………………………………..………….45 Figure 4.3.4: Electric torque Curve………………………………………………….45 Figure 4.3.5: Armature current Curve………………………………………….……46 Figure 4.3.6: Field current Curve…………………………………………………….46 Figure 5.1: Battery Charging Mode (Regenerating Operation)……………………………………….47

Figure 5.2: Battery Charging Circuit (Regenerative Operation)………………………...…...47 Figure 5.3: Circuit diagram with measuring scope………………………………………..…48 Figure 5.3.1: Generator Output Voltage Curve…………………………………..….49 Figure 5.3.2: Output Voltage Curve of boost converter……………………………..49 Figure 5.3.3: Output Voltage Curve of DC to DC converter……………………..…50 Figure 5.3.4: Generator speed curve…………………………………………………50 Figure 5.3.5: Generator field current curve…………………………………………..51 Figure 5.3.6: Battery voltage curve…………………………………………………..51 Figure 5.3.7: Battery current curve…………………………………………………..52

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Figure 5.3.8: SOC(%) curve………………………………………………………….52 Figure 6.1. Electric vehicle power train system……………………………………………...54

LIST OF TABLES Table 2.1: Data table for different output voltage for the corresponding input voltage….….14 Table 2.2: Data table for different output voltage for the corresponding input voltage…..…23 Table 2.3: Data table for different output voltage for the corresponding input voltage……..30 Table 2.4: Comparison between Conventional, PI & PID controlled Bi directional DC to DC Converter……………………………………………………………………………………..30 Table 3.1: Data table for different output voltage for the corresponding input voltage (For Conventional Boost Converter)………………………………………………………………36 Table 3.2: Data table for different output voltage for the corresponding input voltage (For Combine IGBT-MOSFET switched Boost Converter)………………………………………40

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CHAPTER: 1 INTRODUCTION

1.1 Background Batteries are the primary energy-storage devices in ground vehicles. Now a day’s battery fed electric drives are commonly being used for electric vehicles applications, due to various advantages, such as: nearly zero emission, guaranteed load leveling, good transient operation and energy recovery during braking operation. To fulfill these requirements converters with bidirectional power flow capabilities are required to connect the accumulator (battery) to the dc link of the motor drive system. Battery fed electric vehicles (BFEVs) is required to function in three different modes namely: acceleration mode, normal (steady-state) mode and braking (regenerative) mode. During acceleration and normal modes the power flow is from battery to motor where as during braking or regenerative mode the kinetic energy of the motor is converted into electrical energy and fed back to battery.

1.2 Motivation The large number of automobiles in use around the world has caused and continues to cause serious problems on environment and human life. Air pollution, global warming, and the rapid depletion of the earth’s petroleum resources are now serious problems. Electric Vehicles (EVs) have been typically proposed to replace conventional vehicles in the near future. So here our prime concern is to increase the overall efficiency of the Electric Vehicles.

1.3 Contribution of the Thesis a) Designing of a PI controlled high efficient Bidirectional DC to DC Converter. b) Designing of a high efficient Boost Converter by using IGBT & MOSFET combination. c) Implementation of these two devices for Electric vehicle system.

Figure 1.1: Battery Discharging Mode (Normal or Motoring Operation)

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Figure 1.2: Battery Charging Mode (Regenerating Operation)

1.4 Implementation of the System The use of a Bi-directional dc-dc converter in electric vehicles (EVs) application allows a suitable control of both motoring and regenerative braking operations. In the regenerative operation a boost converter is used to boost the low generated voltage to a high input voltage of Bidirectional converter. And finally these Bi-directional converter & Boost Converter is implemented for the electric vehicle system and will increase the overall efficiency.

1.5 Software Simulation will be shown by MATLAB.

1.6 Organization of the Thesis

The thesis work has been organized as follows: Chapter 2:

Literature Review.

Chapter 3:

Modeling of bi directional DC to DC converter.

Chapter 4:

Modeling of Boost Converter

Chapter 5:

Implementing PI controlled bidirectional DC to DC converter and boost converter for Electric Vehicle system.

Chapter 6:

Conclusion

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CHAPTER: 2 LITERATURE REVIEW 2.1 DC to DC converter A DC to DC converter is a power converter that converts a current from one voltage unit to another. The purpose of a DC to DC converter is to convert one voltage from one end to another voltage at the other end, thus a user can have the option to use another voltage also. DC stands for direct current. DC to DC converter can be operated in buck mode or boost mode. In buck mode load end voltage is lower than the supply end voltage and in boost mode load end voltage is higher than the supply end voltage.

2.2 Bidirectional DC to DC converter A DC to DC converter where the power flow is in both the directions that converter is called bidirectional DC to DC converter. We can achieve bi-directional power flow by parallel the buck converter and boost converter. Bidirectional DC to DC converters have attracted a great deal of applications in the area of the energy storage systems for Hybrid Vehicles, Renewable energy storage systems, Uninterruptable power supplies and Fuel cell storage systems [14]. Traditionally they were used for the motor drives for the speed control and regenerative braking. Bidirectional DC to DC converters are employed when the DC bus voltage regulation has to be achieved along with the power flow capability in both the direction.

Figure 2.1: A Block diagram of a bidirectional DC- DC converter 2.2.1 Operation Mode of Bidirectional DC to DC Converter Bidirectional DC to DC converter operates in two modes: 1. Buck mode 2. Boost mode

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Buck mode is the step down mode where receiving end voltage becomes lower than supply end voltage. And boost mode is the step up mode where receiving end voltage becomes higher than supply end voltage. 2.2.2 Classification of Bidirectional DC to DC converter Basically, bidirectional DC to DC converters can be classified into two categories depending on the isolation between the input and output side: 1. Non-Isolated Bidirectional DC to DC converters 2. Isolated Bidirectional DC to DC converters

Figure 2.2: A Block diagram of an isolated bidirectional DC- DC converter

An Isolated DC to DC converter can be worked in three steps. In first steps the switches convert the supply dc voltage to equivalent ac voltage. In second step the transformer transforms this ac voltage to a higher ac voltage. And finally a rectifier circuit converts this high ac voltage to a high dc voltage. 2.3 PI and PID Controller 2.3.1 Proportional and Integral Control (PI Control) PI Controller (proportional-integral controller) is a feedback controller which drives the plant to be controlled with a weighted sum of the error (difference between the output and desired set-point) and the integral of that value. It is a special case of the common PID controller in which the derivative (D) of the error is not used.

Figure 2.3: Proportional Integral (PI) Controller block diagram 16 | P a g e

2.3.2 Advantages of the PI Controller 1. The integral term in a PI controller causes the steady-state error to reduce to zero, which is not the case for proportional-only control in general. 2. The lack of derivative action may make the system steadier in the steady state in the case of noisy data. This is because derivative action is more sensitive to higherfrequency terms in the inputs. 2.3.3 PI Control Strategy The control circuit of the bidirectional converter is shown in Figure 2.8. To control the speed of the dc drive; one possible control option is to control the output voltage of the bidirectional converter. To control the output voltage of the bidirectional converter for driving the vehicle at desired speed and to provide fast response without oscillations to rapid speed changes a PI controller is used and it shows satisfactory result. In this control technique the rms signal is sensed and compared with a reference signal. The error signal is processed through the PI controller. The signal thus obtained is compared with a high frequency saw tooth signal equal to switching frequency to generate pulse width modulated (PWM) control signals [16].

Figure 2.4: Block diagram of PI control Strategy 2.3.4 Proportional- Integral-Derivative Control (PID Control) PID controller has the optimum control dynamics including zero steady state error, fast response (short rise time), no oscillations and higher stability. The necessity of using a derivative gain component in addition to the PI controller is to eliminate the overshoot and the oscillations occurring in the output response of the system. One of the main advantages of the PID controller is that it can be used with higher order processes including more than single energy storage. The combination of proportional, integral, and derivative terms is important to increase the speed of the response, to eliminate the steady state error and also to reduce the overshoot. The PID controller block is shown in figure 2.5.

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Figure 2.5: PID Controller block diagram 2.3.5 Limitations of PID Control While PID controllers are applicable to many control problems, and often perform satisfactorily without any improvements or only coarse tuning, they can perform poorly in some applications, and do not in general provide optimal control. The fundamental difficulty with PID control is that it is a feedback system, with constant parameters, and no direct knowledge of the process, and thus overall performance is reactive and a compromise. While PID control is the best controller in an observer without a model of the process, better performance can be obtained by overtly modeling the actor of the process without resorting to an observer. PID controllers, when used alone, can give poor performance when the PID loop gains must be reduced so that the control system does not overshoot, oscillate or hunt about the control setpoint value. They also have difficulties in the presence of non-linearity, may trade-off regulation versus response time, do not react to changing process behavior (say, the process changes after it has warmed up), and have lag in responding to large disturbances.

2.4 Methodology 2.4.1 PI controller for Bidirectional DC to DC Converter A bi-directional converter is a DC to DC converter where the power can flows is in both the directions as supply end to load end and also load end to supply end. In a conventional bi directional converter PWM (Pulse width modulation) pulse is used for the generation of triggering pulse of the switches [17]. Here output voltage is changed in a high variety with small change in the supply voltage because here the firing angle is fixed. So we cannot get the almost same output voltage by the conventional bi directional converter for small variety of supply voltage. A PI controlled bi-directional converter is used for the higher efficiency. PI Controller (proportional-integral controller) is a special case of the PID controller in which the derivative (D) of the error is not used. It is a feedback controller which drives the plant to be 18 | P a g e

controlled with a weighted sum of the error (difference between the output and desired setpoint) and the integral of that value. This arrangement is used to provide the triggering pulse to the IGBTS. PI first take the value of output voltage of the converter then compare it with the required output voltage or set value and then it provides trigger signal to obtain a fixed value of output voltage though the input voltage of the converter is changed.

2.4.2 Idea of designing Boost Converter by using IGBT & MOSFET combination Generally, for high power applications, one can use inverter with different topologies like multilevel inverter, NPC converter etc. In those topologies to achieve highest efficiency at constant level with the paralleling of MOSFET and IGBT, it is possible to achieve a nearly constant efficiency at the highest level. For High power application, it is beneficial to use MOSFET and IGBT for high efficiency and good switching frequency.

Figure 2.6: Combination of IGBT & MOSFET switch for Boost converter

2.5 Electric vehicle An electric vehicle (EV), also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion. Three main types of electric vehicles exist, those that are directly powered from an external power station, those that are powered by stored electricity originally from an external power source, and those that are powered by an on-board electrical generator, such as an internal combustion engine (hybrid electric vehicles) or a hydrogen fuel cell. EVs include plug-in electric cars, hybrid electric cars, hydrogen vehicles, electric trains, electric lorries, electric airplanes, electric boats, electric motorcycles and scooters and electric spacecraft. Diesel submarines operating on battery power are, for the duration of the battery run, electric submarines, and some of the lighter UAVs are electrically-powered. Proposals exist for electric tanks. During the last few decades, environmental impact of the petroleum-based transportation infrastructure, along with the peak oil, has led to renewed interest in an electric transportation infrastructure. EVs differ from fossil fuel-powered vehicles in that the electricity they consume can be generated from a wide range of sources, including fossil fuels, nuclear 19 | P a g e

power, and renewable sources such as tidal power, solar power, and wind power or any combination of those. The carbon footprint and other emissions of electric vehicles varies depending on the fuel and technology used for electricity generation. The electricity may then be stored on board the vehicle using a battery, flywheel, or super-capacitors. Vehicles making use of engines working on the principle of combustion can usually only derive their energy from a single or a few sources, usually non-renewable fossil fuels. A key advantage of hybrid or plug-in electric vehicles is regenerative braking due to their capability to recover energy normally lost during braking as electricity is stored in the on-board battery.

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CHAPTER: 3 MODELING OF BIDIRECTIONAL DC TO DC CONVERTER 3.1 CONVENTIONAL BIDIRECTIONAL DC TO DC CONVERTER 3.1.1 Steps of Designing a Conventional Bidirectional DC to DC Converter A Bidirectional DC to DC converter is basically a type of switching power supply. The steps of designing a Bidirectional DC to DC converter are given below:

Step 1:The switches convert the input DC voltage to AC voltage.

Figure 3.1: Inverter Figure 3.1 represents a full bridge inverter circuit which inverters the DC voltage to AC voltage. The inverter circuit consists of IGBT switches.

Step 2: A transformer is cascaded with the Inverter circuit.

Figure 3.2: Inverter cascaded with transformer

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Figure 3.2 represents the inverter circuit cascaded with transformer which transforms the supply AC voltage from inverter to the desired AC voltage. Step 3: A rectifier circuit is added with the secondary side of the transformer.

Figure 3.3: Conventional Bidirectional DC to DC converter Figure 3.3 represents the Conventional Bidirectional DC to DC converter. A rectifier circuit is cascaded with the secondary side of the transformer to converts the AC voltage to DC voltage and a filter circuit is added for smoothing the DC voltages. Finally it consists of an input section, an inverter section, a rectifier section and an output section. 3.2 SIMUATION AND RESULT 3.2.1 Circuit Diagram of Buck Operation

Figure 3.4: Conventional Bidirectional DC to DC converter (Buck mode). Figure 3.4 represents the buck mode of Conventional Bidirectional DC to DC converter. In buck operation receiving end voltage became lower than the supply end voltage. Here in the supply end, a battery supplied 380 volt DC. It is supplied to transformer high voltage side. 22 | P a g e

The inverter section in high voltage side inverts the DC voltage to AC voltage. The inverter section is consists with four IGBT. The transformer transforms the high AC voltage to low AC voltage. And finally the rectifier section in the transformer low voltage side makes the low AC voltage to low DC voltage. The rectifier section is also consists with four IGBT. The triggering pulse of IGBTs is supplied from two different PWM generators. 3.2.2 Simulation Output Figure 3.4.1 shows the input curve of the voltage for 380 Volt.

Figure 3.4.1: Input Curve. Figure 3.4.2 shows the Transformer primary side Output waveform where the peak input voltage is 380 volt AC.

Figure 3.4.2: Transformer primary side Output. 23 | P a g e

Figure 3.4.3 shows the Transformer secondary side Output waveform where the transformer secondary side supplies 48 volt AC.

Figure 3.4.3: Transformer secondary side output. Figure 3.4.4 shows the Output waveform of conventional Bidirectional DC to DC converter (buck mode) where the peak voltage is 32 volt DC.

Figure 3.4.4: Output Curve.

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3.2.3 Circuit Diagram of Boost Operation

Figure 3.5: Conventional Bidirectional DC to DC converter (Boost mode). Figure 3.5 represents the boost mode of Conventional Bidirectional DC to DC converter. In boost operation receiving end voltage became higher than the supply end voltage. Here in the supply end, a battery supplied 48 volt DC. It is supplied to transformer low voltage side. The inverter section in low voltage side inverts the low DC voltage to low AC voltage. The inverter section is consists with four IGBT. The transformer transforms the low AC voltage to high AC voltage. And finally the rectifier section in the transformer high voltage side makes the high AC voltage to high DC voltage. The rectifier section is also consists with four IGBT. The triggering pulse of IGBTs is supplied from two different PWM generators. 3.2.4 Simulation Output Figure 3.5.1 shows the input curve of the voltage for 48 Volt.

Figure 3.5.1: Input Curve. 25 | P a g e

Figure 3.5.2 shows the Transformer primary side Output waveform where the peak input voltage is 48 volt AC.

Figure 3.5.2: Transformer primary side output.

Figure 3.5.3 shows the Transformer secondary side Output waveform where transformer secondary side supplies 380 volt AC

Figure 3.5.3: Transformer secondary side output.

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Figure 3.5.4 shows the Output waveform of conventional Bidirectional DC to DC converter (boost mode) where the output voltage is 110 Volt DC.


3.2.5 Data table of different output voltage for the corresponding input voltage (For Conventional Bi directional DC to DC converter) Table 2.1: Data table of different output voltage for the corresponding input voltage Boost operation: Input (V) 45 48 50

Output (V) 105 110 118

Input (V) 375 380 385

Output (V) 30 32 33.5

Buck operation:

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3.3 MODELING OF PI CONTROLLED BIDIRECTIONAL DC - DC CONVERTER

3.3.1 Steps of Designing an PI Controlled Bidirectional DC to DC converter The steps of designing a Bidirectional DC to DC converter are given below: Step 1: The switches convert the input DC to AC.

Figure 3.6: Inverter. Figure 3.6 represents a full bridge inverter circuit which inverters the DC voltage to AC voltage. The inverter circuit consists of IGBT switches.

Step 2: A transformer is cascaded with the Inverter circuit.

Figure 3.7: Inverter cascade with Transformer Figure 3.7 represents the inverter circuit cascaded with transformer which transforms the supplied AC voltage to the desired AC voltage.

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Step 3: A rectifier circuit is added with the secondary side of the transformer.

Figure 3.8: Bidirectional DC to DC converter circuit without control circuit Figure 3.8 represents the Bidirectional DC to DC converter. A rectifier circuit is cascaded with the secondary side of the transformer to converts the AC to DC voltage and a filter circuit is added for smoothing the DC voltages which is the complete Bidirectional DC to DC converter. Finally it consists of an input section, an inverter section, a rectifier section and an output section.

Step 4: Designing a PI control circuit for providing the triggering pulse to the IGBTS. This control circuit is connected with both sides.

Figure 3.9: PI controlled Bidirectional DC to DC converter. Figure 3.9 represents the circuit of a PI controlled bidirectional DC to DC converter. The circuit consists of an input section, an inverter section, a rectifier section and an output section. In the input section battery is used as source. In both inverter section and rectifier section eight IGBTs (four on each side) is used as inverter and rectifier element. The triggering pulse of IGBTs is controlled by the PID controller. The circuit works in two different mode buck mode and boost mode.

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3.3.2 PI Control Circuit

Figure 3.10: PI Control Circuit. PI controller is used to increase the working efficiency. This arrangement is used to provide the triggering pulse to the IGBTS.PI first take the value of output voltage of the converter then compare it with the required output voltage or set value and then it provides trigger signal to obtain a fixed value of output voltage though the input voltage of the converter is changed. 3.4 SIMUATION AND RESULT 3.4.1 Circuit Diagram of Buck Operation

Figure 3.11: Bidirectional DC to Dc converter with PI controller (Buck mode). Figure 3.11 represents the buck mode of PI controlled bidirectional DC to DC converter. In buck operation receiving end voltage became lower than the supply end voltage. Here in the supply end, a battery supplied 380 volt DC. It is supplied to transformer high voltage side. The inverter section in high voltage side inverts the DC voltage to AC voltage. The transformer transforms the high AC voltage to low AC voltage. And finally the rectifier section in the transformer low voltage side makes the low AC voltage to low DC voltage.

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3.4.2 Simulation Output Figure 3.11.1 shows the input curve of the voltage for 380 Volt.

Figure 3.11.1: Input Curve. Figure 3.11.2 shows the Transformer primary side Output waveform where the peak input voltage is 380 volt AC.

Figure 3.11.2: Transformer primary side output at buck condition.

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Figure 3.11.3 shows the Transformer secondary side Output waveform where transformer secondary side supplies 48 volt AC.

Figure 3.11.3: Transformer secondary side output at buck condition. Figure 3.11.4 shows the Output waveform of PI controlled Bidirectional DC to DC converter (buck mode) where the output voltage is 48 Volt DC.


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Figure 3.12: Bidirectional DC to DC converter with PI controller (Boost mode). Figure 3.12 represents the boost mode of PI controlled bidirectional DC to DC converter. In boost operation receiving end voltage became higher than the supply end voltage. Here in the supply end, a battery supplied 48 volt DC. It is supplied to transformer low voltage side. The inverter section in low voltage side inverts the low DC voltage to low AC voltage. The transformer transforms the low AC voltage to high AC voltage. And finally the rectifier section in the transformer high voltage side makes the high AC voltage to high DC voltage. 3.4.4 Simulation Output Figure 3.12.1 shows the input curve of the voltage for 48 Volt DC.

Figure 3.12.1: Input Curve.

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Figure 3.12.2 shows the Transformer primary side Output waveform where the peak input voltage is 48volt AC.

Figure 3.12.2: - Transformer primary side output at boost condition.

Figure 3.12.3 shows the Transformer secondary side Output waveform where transformer secondary side supplies 380 volt AC.

Figure 3.12.3: - Transformer primary side output at boost condition.

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Figure 3.12.4 shows the Output waveform of PI controlled Bidirectional DC to DC converter (boost mode) where the output voltage is 380 Volt DC.


3.4.5 Data table of different output voltage for the corresponding input voltage (For PI Controlled Bi directional DC to DC Converter) Table 2.2: Data table for different output voltage for the corresponding input voltage Boost operation Input (V) 45 48 50

Output (V) 379 380 381.5

Input (V) 375 380 385

Output (V) 46 47.5 48.5

Buck operation

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3.5 MODELING OF PID CONTROLLED BIDIRECTIONAL DC - DC CONVERTER

3.5.1 PID controlled Bidirectional DC to DC converter operation

Figure 3.13: PID controlled Bidirectional DC to DC converter

Figure 3.13 represents the circuit of a PID controlled bidirectional DC to DC converter. The circuit consists of an input section, an inverter section, a rectifier section and an output section. In the input section battery is used as source. In both inverter section and rectifier section eight IGBTs (four on each side) is used as inverter and rectifier element. The triggering pulse of IGBTs is controlled by the PID controller. The circuit works in two different mode buck mode and boost mode. 3.5.2 PID Control Circuit

Figure 3.14: PID Control Circuit. Figure 3.14 represents a PID Controller circuit. This arrangement is used to provide the triggering pulse to the IGBTS. PID first takes the value of output voltage of the converter then compares it with the required output voltage or set value and then it provides trigger signal to obtain a fixed value of output voltage though the input voltage of the converter is changed.

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3.6 SIMUATION AND RESULT 3.6.1 Circuit Diagram of Buck Operation

Figure 3.15: Bidirectional DC to Dc converter with PID controller (Buck mode). Figure 3.15 represents the buck mode of PID controlled bidirectional DC to DC converter. In buck operation receiving end voltage became lower than the supply end voltage. Here in the supply end, a battery supplied 380 volt DC. It is supplied to transformer high voltage side. The inverter section in high voltage side inverts the DC voltage to AC voltage. The transformer transforms the high AC voltage to low AC voltage. And finally the rectifier section in the transformer low voltage side makes the low AC voltage to low DC voltage. 3.6.2 Simulation Output Figure 3.15.1 shows the input curve of the voltage for 380 volt.


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Figure 3.15.2 shows the transformer primary side output waveform where the peak input voltage is 380 volt AC.

Figure 3.15.2: Transformer primary side output at buck condition.

Figure 3.15.3 shows the transformer secondary side output waveform where transformer secondary side supplies 44 volt AC.

Figure 3.15.3: Transformer secondary side output at buck condition.

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Figure 3.15.4 shows the output curve of buck operation, for 380 volt input. The output voltage is 44 volt.



Figure 3.16: Bidirectional DC to Dc converter with PID controller (Boost mode). Figure 3.16 represents the boost mode of PID controlled bidirectional DC to DC converter. In boost operation receiving end voltage became higher than the supply end voltage. Here in the supply end, a battery supplied 48 volt DC. It is supplied to transformer low voltage side. The inverter section in low voltage side inverts the low DC voltage to low AC voltage. The transformer transforms the low AC voltage to high AC voltage. And finally the rectifier section in the transformer high voltage side makes the high AC voltage to high DC voltage.

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3.6.4 Simulation Output Figure 3.16.1 shows the input curve of the voltage for 48 volt.


Figure 3.16.2 shows the transformer primary side output waveform where the peak input voltage is 48 volt AC.

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Figure 3.16.2: - Transformer primary side output at boost condition. Figure 3.16.3 shows the transformer secondary side output waveform where transformer secondary side supplies 350 volt AC.

Figure 3.16.3: - Transformer secondary side output at boost condition.

Figure 3.16.4 shows the output curve of boost condition for 48 volt input. The Output voltage is 350 volt.

Figure 3.16.4: Output Curve. 41 | P a g e

3.6.7 Data table of different output voltage for the corresponding input voltage (For PID Controlled Bi directional DC to DC Converter)

Table 2.3: Data table for different output voltage for the corresponding input voltage Boost operation Input (V) 45 48 50

Output (V) 340 351 360

Input (V) 375 380 385

Output (V) 43 44 46

Buck operation

3.7 COMPARISON BETWEEN CONVENTIONAL, PI CONTROLLED AND PID CONTROLLED BI-DIRECTIONAL DC TO DC CONVERTER

Table 2.4: Comparison between Conventional, PI & PID controlled Bi directional DC to DC Converter

Topic

Conventional Bidirectional DC to DC Converter

PI Controlled Bidirectional DC to DC Converter

PID Controlled Bidirectional DC to DC Converter

Output Voltage (Boost condition)

Vi=45 V Vo=102.3 V Vi=48 V Vo=110 V Vi=50 V Vo=118 V Output variation is more with the input variation.

Vi=45 V Vo=379V Vi=48 V Vo=380V Vi=50 V Vo=381.5V Output variation is less with the input variation.

Vi=45 V Vo=340V Vi=48 V Vo=351V Vi=50 V Vo=360V Output variation is more than PI with the input variation.

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Output curve(for 48 V boost condition)

Efficiency (for 48 V boost condition)

Vi=48V

Vo=110 V

Vi=48V

Vo=380V

Vi=48V

Vo=351V

More efficient.

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CHAPTER: 4 MODELLING OF BOOST CONVERTER 4.1 MODELLING OF CONVENTIONAL BOOST CONVERTER 4.1.1 Boost Converter (Step-up Converter) A boost converter is a DC-to-DC power converter with an output voltage greater than its input voltage. It is a class of switched-mode power supply (SMPS) containing at least two semiconductor switches (a diode and a MOSFET or IGBT) and at least one energy storage element, a capacitor, inductor, or the two in combination. Filters made of capacitors (sometimes in combination with inductors) are normally added to the output of the converter to reduce output voltage ripple. Power for the boost converter can come from any suitable DC sources, such as batteries, solar panels, rectifiers and DC generators. A process that changes one DC voltage to a different DC voltage is called DC to DC conversion. A boost converter is a DC to DC converter with an output voltage greater than the source voltage. A boost converter is sometimes called a step-up converter since it “steps up” the source voltage. Since power (P=VI) must be conserved, the output current is lower than the source current.

Figure 4.1: A Block diagram of a boost converter 4.1.2 Operating principle The key principle that drives the boost converter is the tendency of an inductor to resist changes in current by creating and destroying a magnetic field. In a boost converter, the output voltage is always higher than the input voltage. A schematic of a boost power stage is shown in Figure 4.1 (a) When the switch is closed, current flows through the inductor in clockwise direction and the inductor stores some energy by generating a magnetic field. Polarity of the left side of the inductor is positive.

Figure 4.1.1: When switch is closed 44 | P a g e

(b) When the switch is opened, current will be reduced as the impedance is higher. The magnetic field previously created will be destroyed to maintain the current flow towards the load. Thus the polarity will be reversed (means left side of inductor will be negative now). As a result two sources will be in series causing a higher voltage to charge the capacitor through the diode D.

Figure 4.1.2: When switch is open If the switch is cycled fast enough, the inductor will not discharge fully in between charging stages, and the load will always see a voltage greater than that of the input source alone when the switch is opened. Also while the switch is opened, the capacitor in parallel with the load is charged to this combined voltage. When the switch is then closed and the right hand side is shorted out from the left hand side, the capacitor is therefore able to provide the voltage and energy to the load. During this time, the blocking diode prevents the capacitor from discharging through the switch. The switch must of course be opened again fast enough to prevent the capacitor from discharging too much. 4.2 SIMUATION AND RESULT 4.2.1 Circuit Diagram of Conventional Boost Converter

Figure 4.2: Circuit diagram of conventional boost converter Figure 4.2 shows the circuit diagram of conventional boost converter. Here MOSFET is used as switch. By turning ON or OFF the switch higher DC output voltage than the supply voltage is achieved. When the switch is ON, energy is stored in the inductor. And when the 45 | P a g e

switch is OFF two sources (DC source and Inductor) are in series causing a higher voltage to charge the capacitor i.e. load will always see a voltage greater than that of input source when the switch is OFF. When the switch is than ON again the capacitor is therefore able to provide the voltage and energy to the load. During this time the blocking diode prevents the capacitor from discharging through the switch. 4.2.2 Simulation Output Figure 4.2.1 shows the input curve of the voltage for 48 volts.

Figure 4.2.1: Input Voltage Curve Figure 4.2.2 shows the input current curve of conventional boost converter where the peak value of input current is 139.6 amp.

Figure 4.2.2: Input Current Curve

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Figure 4.2.3 shows the output current curve of conventional boost converter where the peak value of output current is 11.1 amp.

Figure 4.2.3: Output Current Curve. Figure 4.2.4 shows the output curve of the voltage for 48 volt input. The peak output voltage is 333 volt.

Figure 4.2.4: Output Voltage Curve.

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4.2.3 Data table for different output voltage for the corresponding input voltage (For conventional Boost Converter) Table 3.1: Data table for different output voltage for the corresponding input voltage (For Conventional Boost Converter)

Input voltage (V) 48

Input current (A) 139.6

Input power (W) 6700.8

Output voltage (V) 333

Output current (A) 11.1

Output power (W) 3696.3

Efficiency (%)

24

69.71

1675.04

166.3

5.543

921.80

55%

55%

4.3 MODELLING OF BOOST CONVERTER BY COMBINATION OF MOSFET AND IGBT With the race towards highest efficiency, innovative topologies are more often considered for the development of new power conversion products. A device with the low ON state voltage of an IGBT and the fast switching characteristics of a MOSFET can be achieved by paralleling an IGBT with a MOSFET. However, in order to gain these advantages, the IGBT MOSFET pair must be carefully controlled. At switch on the Gate of the MOSFET is direct paralleled with the IGBT gate because the MOSFET will be faster and take over the switch on losses. But at switch off, the MOSFET has to be delayed to release the IGBT from switch off losses. MOSFET connected in parallel with IGBT can create soft switching condition for IGBT. Also with the paralleling of MOSFET and IGBT, it is possible to achieve a nearly constant efficiency at the highest level [43].

Figure 4.3: Parallel Connection of IGBT and MOSFET.

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4.3.1 Parallel operation of IGBT and MOSFET The parallel operation of MOSFET and IGBT has been termed as the mixed parallel operation mode. In this mode, a MOSFET and an IGBT operate in parallel as shown in Fig 1. In the on-state, MOSFET and IGBT conduct simultaneously. IGBT conducts most of the current while the MOSFET carries only a part because the on-state drop of the IGBT is smaller than that of the MOSFET. The IGBT is turned off first and the load current is transferred to the MOSFET. The IGBT exhibits tail current but its terminal voltage is maintained low due to parallel conducting the MOSFET. The turn-off losses in the IGBT are thus reduced. After a short delay, Td, MOSFET is turned off. The turn-off loss in IGBT depends on Td, longer the Td lower will be the loss [43]. 4.3.2 Advantages The combination addresses two basic improvements in efficiency:  Boosting the efficiency at high load range by rendering the static losses of IGBT and dynamic losses of MOSFET.  Boosting the efficiency at low load range by rendering both the dynamic losses and static losses to MOSFET. 4.4 SIMUATION AND RESULT 4.4.1 Circuit Diagram of Boost Converter by combination of MOSFET and IGBT

Figure 4.4: Circuit diagram of boost converter (Combination). Figure 4.4 shows the boost converter by combination of parallel IGBT and MOSFET switch. This type of boost converter is proposed due to the moderate efficiency of conventional boost converter. Here MOSFET has high ON state loss and IGBT has high OFF state loss. So duty cycle of the MOSFET is set higher than the IGBT. During ON state IGBT conduct most of the current. Thus reduce the ON state loss of MOSFET. And then IGBT is turned OFF first and load current is than transfer to the MOSFET. And after a time delay MOSFET is turn OFF. Thus reduce the OFF state loss of IGBT.

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4.4.2 Simulation Output Figure 4.4.1 shows the input curve of the voltage for 48 volts.

Figure 4.4.1: Input Voltage Curve.

Figure 4.4.2 shows the input current curve of combined MOSFET and IGBT switch boost converter where the peak value of input current is 113.5 amp.

Figure 4.4.2: Input Current Curve

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Figure 4.4.3 shows the output current curve of combined MOSFET and IGBT switch boost converter where the peak value of input current is 9 amp.

Figure 4.4.3: Output Current Curve

Figure 4.4.4 shows the output curve of the voltage for 48 volt input. The peak output voltage is 450 volt.

Figure 4.4.4: Output Voltage Curve 51 | P a g e

4.4.3 Data table for different output voltage for the corresponding input voltage(For Combine IGBT-MOSFET switched Boost Converter) Table 3.2: Data table for different output voltage for the corresponding input voltage (For Combine IGBT-MOSFET switched Boost Converter) Input voltage (V) 48

Input current (A) 113.5

Input power (W) 5448

Output voltage (V) 450.7

Output current (A) 9.014

Output power (W) 4062.6

Efficiency (%)

24

56.08

1345.92

222.7

4.453

991.6831

74%

74.5%

4.5 COMPARISON BETWEEN CONVENTIONAL BOOST CONVERTER AND BOOST CONVERTER BY COMBINATION OF MOSFET& IGBT

80% 70%

60% 50% Conventional

40%

IGBT MOSFET Combinition 30% 20% 10% 0% 24 V

48 V

Figure 4.5: Comparison between Conventional & Combined IGBT-MOSFET switch Boost converter In the above chart, for both 24V and 48V input voltage higher efficiency is obtained for the boost converter designed by the combination of IGBT and MOSFET then the conventional boost converter. So for Electric Vehicle application boost converter which is designed by the combination of IGBT and MOSFET is used.

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CHAPTER: 5 IMPLEMENTING PI CONTROLLED BI DIRECTIONAL CONVERTER AND BOOST CONVERTR FOR ELECTRIC VEHICLE 5.1 Battery Discharging Mode (Normal or Motoring Operation) Battery discharging mode is one of the two modes of operation of electrical vehicle. It is the normal operational mode where power is supplied to the motor to drive the vehicle from the storage element or battery [41]. 5.2 Block Diagram

Low Voltage Battery

Bidirectional Converter with PI Controller

High Voltage Motor

Figure 5.1: Battery Discharging Mode (Normal or Motoring Operation) The energy stored in the battery is supplied to the motor through a PI controlled bidirectional converter to convert the low voltage of battery to high voltage suitable for motor. 5.3 Circuit Diagram of Motoring Operation

Figure 5.2: Battery discharging circuit of Electric Vehicle

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5.4 Circuit Operation Figure 5.2 represents the circuit of DC motor fed isolated DC-DC converter that is motor condition of electric vehicle applications. It is also called the boosting operation or battery discharging operation. It consists of a battery; a PI controlled Bidirectional DC to DC converter and a DC motor. In this circuit, Battery is in one end and the motor is in the other end. 48 volt DC is supplied from the battery to the IGBT switches. The input section of Bidirectional DC to DC converter consisting of IGBT based full bridge inverter. The IGBT switches invert the low voltage DC to low voltage AC. This AC voltage is then input to the transformer’s low voltage side. The transformer transforms the low voltage AC to high voltage AC. The output section of Bidirectional DC to DC converter consisting of IGBT based full bridge rectifier. In both cases The IGBT switch is controlled by the PI controller. Then the rectifier circuit of DC-DC converter rectifies the high voltage AC to high Voltage DC. Now this suitable DC voltage is supplied to the DC motor to run the motor.

5.5 SIMUATION AND RESULT

Figure 5.3: Circuit diagram with measuring scope Figure 5.3 shows the complete circuit of battery discharging mode with measuring scope. The input curve, transformer primary side Output waveform, transformer secondary side Output waveform, output waveform is measured by scope which is shown in the circuit.

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5.5.1 Simulation Output Figure 5.3.1 shows the input curve of the voltage for 48 Volt.

Figure 5.3.1: Input Voltage Curve

Figure 5.3.2 shows the Transformer primary side Output waveform where the peak input voltage is 48 volt AC.

Figure 5.3.2: Transformer primary side voltage.

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Figure 5.3.3 shows the Transformer secondary side Output waveform where the transformer secondary side supplies 380 volt AC. .

Figure 5.3.3: Transformer secondary side voltage

Figure 5.3.4 shows the Output waveform during motor load where firstly output voltage is distorted. After few times it goes to the stable voltage and it is clear that the voltage is 380 Volt.

Figure 5.3.4: Output Curve during motor load

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5.6 Battery Charging Mode (Regenerating Operation) Electric vehicles create their own power for battery recharging through a process known as regenerative braking (regenerating mode). In all-electric vehicle the word "regenerative," in terms of regenerative braking, means capturing the vehicle's momentum (kinetic energy) and turning it into electricity that recharges (regenerates) the onboard battery as the vehicle is slowing down and/or stopping. It is this charged battery that in turn powers the vehicle's electric traction motor [36]. Every time steped on car's brakes, we're wasting energy. Most of it simply dissipates as heat and becomes useless. That energy, which could have been used to do work, is essentially wasted. But automotive engineers have given this problem a lot of thought and have come up with a kind of braking system that can recapture much of the car's kinetic energy and convert it into electricity, so that it can be used to recharge the car's batteries. This system is called regenerative braking. It is an energy recovery mechanism which slows a vehicle or object down by converting its kinetic energy into another form, which can be either used immediately or stored until needed. In electric vehicles, the energy is stored chemically in a battery. These energy is saved in a storage battery is used later to power the motor whenever the car is in electric mode. The most common form of regenerative brake involves using an electric motor as an electric generator. In all-electrics and hybrids, they are more precisely called a motor/generator (M/G). In a traditional braking system, brake pads produce friction with the brake rotors to slow or stop the vehicle. Additional friction is produced between the slowed wheels and the surface of the road. This friction is what turns the car's kinetic energy into heat. With regenerative brakes, on the other hand, the system that drives the vehicle does the majority of the braking. When the driver steps on the brake pedal of an electric or hybrid vehicle, these types of brakes put the vehicle's electric motor into reverse mode, causing it to run backwards, thus slowing the car's wheels. While running backwards, the motor also acts as an electric generator, producing electricity that's then fed into the vehicle's batteries. These types of brakes work better at certain speeds than at others.

5.7 Block Diagram

High Voltage Motor run as generator

Booster

Bidirectional Converter with PI Controller

Low Voltage Battery

Figure 5.4: Battery Charging Mode (Regenerating Operation)

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As when motor works as generator it generate electricity in low voltage. So a booster is used to convert it into high voltage and make it suitable for the input of PI controlled bidirectional converter. The bidirectional converter makes this voltage low to make it suitable for recharging the battery. 5.8 Circuit Diagram of Regenerating Operation

Figure 5.5: Battery Charging Circuit (Regenerative Operation)

5.9 Circuit Operation Figure 5.5 represents the buck operation or battery charging operation. It consist of a boost converter, a DC motor, a PI controlled Bidirectional DC to DC converter and a battery. During the regenerative action the motor acts as generator and it produce a DC voltage. It is comparatively a low voltage. So paralleled IGBT- MOSFET Boost converter is used to convert this low voltage to high voltage. Then this high DC voltage is supplied to the IGBT switches. The input section of Bidirectional DC to DC converter consisting of IGBT based full bridge inverter. The IGBT switches invert the high DC voltage to high AC Voltage. This AC voltage is then input to the transformer high voltage side. The transformer transforms the high AC voltage to low AC voltage. Then the low AC voltage is further goes through the IGBT switches. Here the output section of Bidirectional DC to DC converter consisting of IGBT based full bridge rectifier. Then the rectifier circuit of DC-DC converter rectifies the low voltage AC to low Voltage DC. The IGBT switches are controlled by the PI controller. Now this suitable DC voltage is used to charge the battery.

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5.10 SIMUATION AND RESULT

Figure 5.6: Circuit diagram with measuring scope Figure 5.6 shows the complete circuit of regenerative mode with measuring scope. The input curve, transformer primary side Output waveform, transformer secondary side Output waveform, output waveform and battery characteristics is measured by scope which is shown in the circuit.

5.10.1 Simulation Output Figure 5.6.1 shows the input curve of the voltage for 48 Volt when the motor is in regenerative operation.

Figure 5.6.1: Generator Output Voltage Curve 59 | P a g e

Figure 5.6.2 shows the Output waveform after boosting for the given input where the peak input voltage is 380 volt DC.

Figure 5.6.2: Output Voltage Curve of boost converter Figure 5.6.3 shows the Transformer primary side Output waveform where the voltage is 380 volt AC.

Figure 5.6.3: Transformer primary side output

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Figure 5.6.4 shows the Transformer secondary side Output waveform where the transformer secondary side supplies 48 volt AC.

Figure 5.6.4: Transformer Secondary side output

Figure 5.6.5 shows the Output waveform Bidirectional DC to DC converter for regenerative mode where the output voltage is 48 Volt DC.

Figure 5.6.5: Output Voltage Curve of DC to DC converter

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5.10.2 Battery Characteristics Figure 5.6.6 shows the battery voltage curve.

Figure 5.6.6: Battery voltage curve Figure 2.6.2 shows the battery current curve.

Figure 4.6.7: Battery current curve

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CHAPTER: 6 CONCLUSION 6.1 Summery In this thesis, a comparative study which presents three examples of DC-DC converter topologies (Conventional isolated DC/DC converter, PI controlled DC/DC converter and PID controlled DC/DC converter). The first structure considers a basic one, the second and third is based on basic Controlled technique. Simulations are carried out for a three DC/DC Converters. In this work we demonstrate the performance of a battery operated electric vehicle system and it shows satisfactory performance at different driving condition. The proposed control technique with PI controller for DC/DC converter and boost converter find suitable for this electric drive. The performance of the BFEV is verified under forward motoring mode and regenerative mode

6.2 Future work An Electric Vehicle is a vehicle that uses a combination of different energy sources, Fuel Cells (FCs), Batteries and Super capacitors (SCs) to power an electric drive system as shown in Fig. In EV, the main energy source is assisted by one or more energy storage devices. Thereby the system cost, mass, and volume can be decreased, and a significant better performance can be obtained. Two often used energy storage devices are batteries and SCS. They can be connected to the fuel cell stack in many ways. A simple configuration is to directly connect two devices in parallel, (FC/battery, FC/SC, or battery/SC). However, in this way the power drawn from each device cannot be controlled, but is passively determined by the impedance of the devices. The impedance depends on many parameters, e.g. temperature, state-of-charge, health, and point of operation. Each device might therefore be operated at an inappropriate condition, e.g. health and efficiency. The voltage characteristics also have to match perfectly of the two devices, and only a fraction of the range of operation of the devices can be utilized, e.g. in a fuel cell battery configuration the fuel cell must provide almost the same power all the time due to the fixed voltage of the battery, and in a battery/super capacitor configuration only a fraction of the energy exchange capability of the super capacitor can be used. This is again due to the nearly constant voltage of the battery. By introducing DC/DC converters one can chose the voltage variation of the devices and the power of each device can be controlled.

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Figure 5.1 Electric vehicle power train system. In reference (Schaltz & Rasmussen, 2008), 10 cases of combining the fuel cell with the battery, SCs, or both are investigated. The system volume, mass, efficiency, and battery lifetime were compared. It is concluded that when SCs are the only energy storage device the system becomes too big and heavy. A fuel cell/battery/super capacitors hybrid provides the longest life time of the batteries. It can be noticed that the use of high power DC/DC converters is necessary for EV power supply system. The power of the DC/DC converter depends on the characteristics of the vehicle such as top speed, acceleration time from 0 to 100 Km/h, weight, maximum torque, and power profile (peak power, continuous power) Generally, for passenger cars, the power of the converter is more than 20KW and it can go up to 100 KW.

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