design and implementation of a buck converter by kemjika ananaba

1

ACKNOWLEDGEMENT

To properly recognize all of the people responsible for bringing me to this point in

my life would take a considerable amount of space. Nevertheless, here is an attempt,

mediocre at best, to recognize those individuals responsible for this thesis and

master's degree. Only by the grace of God have I come this far. God's never ending

grace and mercy and his ultimate plan for my life have molded me for his desired

purpose. My parents have given me moral foundations, financial assistance, and

spiritual guidance beyond what any daughter could ask for. My perfect sisters, they

are truly gifts from God. Afe has been my best friend throughout this period.

Mr Calum Cossar was very kind and helpful in serving on my thesis Supervisor

amidst his very busy schedule. Ian Young is a very talented Technician. I have

gained a greater respect for the work he does and the environment in which he

works. The construction of my project could not have been done without him.

Graham Morton took his time in putting me through the basics of Visual Basics

programming.

2

TABLE OF CONTENTS LIST OF FIGURES ............................................................................................................. 4

LIST OF TABLES .............................................................................................................. 7

CHAPTER ONE.................................................................................................................. 8

1.1 Introduction................................................................................................................ 8

1.2 Thesis Structure ......................................................................................................... 9

CHAPTER TWO ............................................................................................................... 11

2.1 Power Converter System ......................................................................................... 11

2.1.1 AC/DC Rectifier ............................................................................................... 11

2.1.2 DC-DC Converter ............................................................................................. 12

2.1.2 Buck Converter ................................................................................................. 14

2.1.3 Power Inverter ................................................................................................... 19

2.2 Portunus Simulation ............................................................................................. 21

2.3 Graphic User Interface ............................................................................................. 21

CHAPTER THREE ........................................................................................................... 23

3.1 Buck Converter Design............................................................................................ 23

3.2 Sizing Components .................................................................................................. 23

3.2.2 Switch Rating .................................................................................................... 26

3.2.3 Diode Rating ..................................................................................................... 28

3.2.4 Output Capacitor Selection ............................................................................... 29

3.3 Open Loop Buck Converter Design ........................................................................ 31

3.3.1 Inductance ......................................................................................................... 31

3.3.2 Capacitance ....................................................................................................... 34

3.3.3 Diode rating....................................................................................................... 35

3.3.4 Switch................................................................................................................ 35

3.4 Closed Loop Buck Converter .................................................................................. 36

3.4.1 Control Topology .............................................................................................. 37

3.5 Graphic User Interface ............................................................................................. 40

3.5.1 Input Parameters ............................................................................................... 41

3.5.2 Output Parameters ............................................................................................. 42

CHAPTER FOUR ............................................................................................................. 43

3

4.1 Simulation Results And Measured Experimental Results ....................................... 43

4.1.3 Buck Converter Testing and Simulation ........................................................... 47

4.1.4 Inverter Simulation ........................................................................................... 53

CHAPTER FIVE ............................................................................................................... 55

5.1 Conclusion ............................................................................................................... 55

REFERENCE .................................................................................................................... 57

APPENDIX A ................................................................................................................... 59

APPENDIX B.................................................................................................................... 60

APPENDIX C.................................................................................................................... 61

APPENDIX D ................................................................................................................... 72

4

LIST OF FIGURES

Fig 1.1 Variation of generator output with wind energy 7

Fig 1.2 PM Generator Test Rig 8

Fig 2.1 Power Converter System 10

Fig 2.2 Three phase Bridge Rectifier 10

Fig 2.3 Rectifier input waveforms and output waveform 11

Fig 2.4 DC-DC Converter 11

Fig 2.5 Pulse-Width Modulation 12

Fig 2.6 Pulse Frequency Modulation 13

Fig 2.7 Basic Buck Converter Circuit 13

Fig 2.8 (a) Circuit with switch ON (b) Circuit with switch OFF 14

Fig 2.9 Voltage and Current Waveforms through the inductor 14

Fig2.10 Continuous and Discontinuous conduction mode Waveform 17

Fig 2.11 Basic DC/AC inverter 18

Fig 2.12 a) Triangular and control waveforms b) PMW signal for S1 and S4 c) PMW

signal for S2 and S3 19

Fig 3.1 Buck Converter With Component Rating 23

Fig 3.2 Inductor Voltage and Inductor current 24

Fig 3.3 Inductor Current at Critical Inductance 25

Fig 3.4 Current Waveform (a) Inductor Current (b) Switch Current (c) Diode Current 26

Fig 3.5 Diode current wave form 27

Fig3.6 Capacitor Current Waveform 29

Fig 3.7 buck converter 31

Fig 3.8 Inductor Current At L= 0.3mh 31

5

Fig 3.9 Inductor Current At L= 0.7mh 31

Fig 3.10 Output voltage and inductor current at L= 0.7mH and C= 362µF 33

Fig 3.11 Output voltage and inductor current at L= 0.7mH and C= 1000µF 34

Fig 3.12 Voltage Output 35

Fig 3.13 Inductor current 35

Fig 3.14 Output current 35

Fig 3.15 Closed Loop Buck Converter 36

Fig 3.16 Closed Loop Buck Control Topology 36

Fig 3.17 Closed Loop Buck Converter and Open Loop Buck Converter 37

Fig 3.18 Error voltage and PWM input signal of the closed loop buck converter 38

Fig 3.19 Input voltage (VMI.1) and output voltage (R1.V) of the closed loop buck

converter 38

Fig 3.20 Input Voltage (VMI.1) and output voltage (R1.V) of the open loop buck

converter 38

Fig 3.21 Closed Loop Converter Output (R1.V) and Open Loop Output (R9.V) with

Voltage input of 32V 38

Fig 3.22 Open-loop Simulation Panel 39

Fig 3.23 Closed-loop Simulation Panel 40

Fig 3.24 User Interface – Controller Interaction 41

Fig 4.1 Generator Dynamometer 43

Fig4.2 Variation of generation voltage verses speed 44

Fig 4.3 Generator Voltage Output at 500rpm 44

Fig 4.4 Three Phase Voltage Output from Portunus Generator Model 45

Fig 4.5: Rectifier output without a Capacitor (a) using Portunus simulation (b)

experimental result (c) Simulation and experimental results 45

Fig 4.6 Portunus Rectifier Model 45

6

Fig 4.7 Rectifier output with 1000uF Capacitor 46

Fig 4.8 Rectifier – Open Loop Buck converter Portunus Model 46

Fig4.9 Buck Output at voltage input of 30V and power output of 50W 47




Fig 4.13 Inverter Model 52

Fig 4.14 Inverter Output 52

Fig 4.15 Experimental Setup 53

Fig 5.1 Efficiency Verses Speed of Generator 54

7

LIST OF TABLES

Table 3.1: Inductor cores and Corresponding Parameters 33

Table 3.2: Inductor parameters 34

Table 4.1: Generator Output voltage with corresponding speed 44

Table 4.2: Variation of generator speed with DC Voltage output 45

Table 4.3: Variation of Buck Output Voltage with input voltage of 30V 48




Table 4.7 Buck Output at varying Power Output (10W- 50W) with generator speed 500 rpm 52



8

CHAPTER ONE

1.1 Introduction

Wind power is the most fast growing energy source in the world and is competitive

against conventional energy sources. Since wind energy is a technology of variable

output as shown in Fig 1.1, it needs to be considered as one aspect of a variable,

dynamic electricity system. Integration of larger wind farms to the utility grid is

increasingly problematic because Distribution and Transmission System Operators

require a wind power station to behave similarly to a conventional power station. A

widely used solution is a synchronous generator combined with a full-scale

converter21

.

Permanent magnet synchronous generators are becoming popular in industry

applications with advantages such as small size, less weight and flexible design

structure. Permanent magnet generators represent a simple and reliable form of

generator construction that is suitable for situations where high reliability is needed.

When uncontrolled the generator output voltage varies over a wide range dependent on

generator speed. It is inconvenient for the voltage supplied to vary over a range

therefore a form of stabilization is needed23

.

courtesy of http://www.wind-energy-the-facts.org

Fig 1.1 Variation of wind energy

http://www.wind-energy-the-facts.org/

9

An inexpensive and efficient power converter for grid connection is required for these

energy systems. The power converter system converts the synchronous generator output

of variable voltage magnitude with variable frequency to a constant sinusoidal voltage

with constant frequency.

The scope of the project centers on the modeling of an electronic power converter

System which is used with a SPEED controller for generator voltage control. In general

the power conversion system consists of a rectifier that forms the dc link that is

regulated to a constant output with the use of a buck converter. The constant dc output is

fed to the externally controlled inverter that performs a D.C to A.C conversion shown in

Fig 1.2. The inverter also determines load frequency.

Fig 1.2 PM Generator Test Rig

1.2 Thesis Structure

This thesis examines the construction of a buck converter and its incorporation in a

power conversion system. The buck converter is built using the circuit simulator and

design tool Portunus to model the circuit. An additional requirement would be to create

10

a Graphic User Interface panel using Visual Basic Language which would allow the user

to input generator control parameters and also display the generator output in a user

friendly style.

As the developer of this project, my specific aims were to:

Study buck converter

Learn about the Portunus Simulation Software.

Test and measure the voltage output of the Synchronous Generator at different

Speeds

Design the buck converter to provide a constant 12V output

Simulate the ac-dc-ac power converter design using Portunus Stimulation

Software.

The operation of the power converter with a description of its major components is

detailed in Chapter two. Chapter three derives the Equations required in the modeling of

the buck converter, and its design. The closed loop buck converter, experiments and

corresponding Portunus simulations are described in detail in Chapter four. Chapter five

will discuss the conclusions reached during the construction of this converter, with

recommendations on how it can be improved.

11

CHAPTER TWO

2.1 Power Converter System

This project has been broken down into three major circuit topologies. The three circuit

topologies are the AC/DC rectifier, DC/DC converter and the DC/AC inverter. These

three components work together to convert a varying AC input voltage to a constant

controlled AC voltage and frequency. A block diagram of the power converter is shown

in Fig 2.1 below

Fig 2.1 Power Converter System

2.1.1 AC/DC Rectifier

A Three Phase Rectifier consists of six diodes and converts the unregulated AC voltage

to unregulated DC voltage. Fig 2.2 highlights a Full-Wave Bridge Rectifier.

Courtesy Of http://services.eng.uts.edu.au/~venkat/pe_html/ch05s1/ch05s1p1.htm

Fig 2.2 Three phase bridge rectifier

The bridge circuit has two halves, the positive half consisting of the Diodes D1, D3 and

D5 and the negative half consisting of the diodes D2, D4 and D6. At any time, one diode

from each half conducts when there is current flow. If the phase sequence of the source

UNREGULATED DC UNREGULATED AC

INPUT REGULATED AC

OUTPUT

CONSTANT DC

3- Phase Rectifier DC – DC Converter Single phase

Inverter

http://services.eng.uts.edu.au/~venkat/pe_html/ch05s1/ch05s1p1.htm

12

be RYB, the Diodes are triggered in the sequence D1 and D2 , D3 , D4, D5 , D6 and D1

and so on. As a result, all current that flows out of the rectifier will be positive13

. The

output waveform is now the absolute value of the input waveform. Fig 2.2 shows both the

input waveforms and the output waveform of the Full-Wave Bridge Rectifier. The three-

phase bridge rectifier circuit has three-legs, each phase connected to one of the three

phase voltages.

t/s

5 m 10 m 15 m 20 m 25 m 30 m 35 m 40 m 45 m 50 m 55 m 60 m 65 m 70 m 75 m 80 m 85 m 90 m 95 m

0

-20

20

40

E2.V

E3.V

Vout.V

E1.V

Fig 2.3 Rectifier input voltage waveforms (E1,E2,E3) and output voltage waveform (Vout)

2.1.2 DC-DC Converter

The DC-DC Converter is a circuit employing switching network that converts a DC

voltage from one level to another DC voltage (Fig 2.4). They are mainly used to provide

a dc power supply with adjustable output voltage, for general use.

INPUT DC VOLTAGE OUTPUT DC VOLTAGE

Fig 2.4 DC-DC Converter

There are basically two ways to achieve the voltage regulation by ;

i) Pulse width Modulation (PWM): this is achieved by varying the on period (Ton) of

the switch while keeping the switching period T is kept constant as shown in Fig 2.5.

Here Duty cycle (D) refers to the ratio of the period for which the switch is kept ON

Time(s)

Switching

Element

Voltage

13

to the cycle period. Usually control by pulse width modulation is the preferred

method since constant frequency operation leads to optimization of LC filter and the

ripple content in output voltage can be controlled.

ii) Pulse Frequency Modulation (PFM): Here the on period (Ton) is kept constant and

the switching period T is varied as shown in Fig 2.6. The design of the LC filter is

difficult in this case.

Fig 2.5 Pulse-Width Modulation

Fig 2.6 Pulse Frequency Modulation

Switch position

Time (s)

Time (s)

Time (s)

1

1

1

0

0

Switch position

1

1

Medium D

Small D

0

0

Time(s)

Time (s)

14

There are three basic types of dc–dc converters: Step-down converter (buck converter)

Step-up converter (Boost Converter) and Step-up-down converter (buck-boost converter)

2.1.2 Buck Converter

Fig 2.7 Basic Buck Converter Circuit

A buck converter or step-down switch mode power supply can also be called a switch

mode regulator. Popularity of a switch mode regulator is due to its fairly high efficiency

and compact size and a switch mode regulator is used in place of a linear voltage

regulator at relatively high output, because linear voltage regulators are inefficient21

.

Since the power devices used in linear regulators have to dissipate a fairly large amount

of power, they have to be adequately cooled, by mounting them on heat sinks which

makes the regulator bulky and large. In applications where size and efficiency are critical,

linear voltage regulators cannot be used16

. Generally any basic switched power supply

consists of five standard components as shown in Fig 2.7.

a. a pulse-width modulating controller,

b. a transistor switch,

c. an inductor ,

d. a capacitor and

e. a diode.

Control by pulse-width modulation is necessary for regulating the output as Duty Cycle is

thus adjusted to obtain the desired Voltage Output. The switch is the heart of the switched

supply and it controls the power supplied to the load11

.

15

An inductor is used in a filter to reduce the ripple in current. This reduction occurs

because inductors are resistance to changes in current. When the current through an

inductor tends to fall, the inductor tends to maintain the current by acting as a source.

A capacitor is used in a filter to reduce ripple in voltage.

The diode used in a switched regulator is usually referred to as a catch diode21

. The

purpose of this diode is not to rectify, but to direct current flow in the circuit and to

ensure that there is always a path for the current to flow into the

inductor.

Courtesy of the practical design of a buck converter by Johor Bahru

Fig 2.8 (a) Circuit with switch CLOSED (b) Circuit with switch OPEN

Figure 2.9 shows the voltage and current waveforms through the inductor when the

switch is open and closed.

16

Courtesy of the practical design of a buck converter by Johor Bahru

Fig 2.9 Voltage and Current Waveforms through the inductor

2.1.2.1 Circuit Description And Operation

This circuit can operate in any of the two states as explained below.

Switch Closed: In the circuit, when the switch is closed, the switch conducts the inductor

current (I L) as shown in Fig 2.8a. This results in a positive voltage across the inductor as

the source voltage would be greater than the output voltage. This voltage causes a linear

increase in the inductor current. When the inductor current rises, the energy stored in it

increases. During this state, the inductor acquires energy3.

VLON = Vin-Vo (2.1)

TON = DT (2.2)

The capacitor smoothens out the inductor’s current changes into a constant output

voltage. Also, the capacitor is large enough so that the output voltage doesn't change

significantly during one switching cycle. At this State the capacitor is getting charged.

When the switch is closed, the elements carrying current are shown in Fig. 2.1 (b). Since

the diode is reversed biased it is not in the picture.

17

Switch Open: When the switch is open, the Inductor maintains current to the load as

shown in Fig 2.8b. As the inductor’s magnetic field collapses, current falls linearly

through the inductor, its fall is determined by the voltage across the inductor and its

inductance.

VLOFF = -Vo (2.3)

TOFF = (1-D)T (2.4)

Since the average voltage across the inductor is zero at steady state, using the volt second

balance equation

VLON TON + VLOFF TOFF = 0 (2.5)

[Vg-Vo] DT + (-Vo) (1-D) T = 0

Vg D – Vo D – Vo + Vo D = 0

Vo = D Vg (assuming ideal components) (2.6)

The inductor maintains current flow by reversing its voltage when the applied voltage is

removed. The diode acts as a voltage controlled switch. It provides a path for the inductor

current once the switch is opened thus the inductor current flows through the diode12

.

2.1.2.2 Modes Of Operation

The dc-dc converters have two distinct modes of operation: Continuous-current

conduction mode (CCM) and discontinuous current- conduction mode (DCM). The buck

converter and its control are designed based on both modes of operation.

18

Fig.2.10 a) Continuous Conduction Mode (b) Discontinuous Current conduction

mode Waveform

i. In the Continuous conduction mode, the inductor current flows continuously that is the

inductor current is always above zero during the OFF period as shown in Fig 2.10b.

Here the voltage output varies linearly with the duty ratio of the switch for a given dc

voltage input. It doesn’t depend on other circuit parameters (inductor and capacitor

value)14

.

Vo/Vg = Ton/T =Duty Ratio.

Therefore in the continuous current conduction mode, the output voltage can be

controlled by controlling the duty cycle in a range of 0-1.

ii. In the Discontinuous conduction mode, the inductor current is discontinuous that is it

remains zero for some time as shown in Fig 2.10a. This is because the load current is

reduced to a value that causes the average inductor current to be reduced to a value

that causes the average inductor voltage to be less than half the inductor ripple

current(1)

. In the OFF period, the power to the load resistance is supplied by the

capacitance alone. Thus in the Discontinuous Conduction mode, the output voltage is

dependent on the circuit component values and the duty ratio of the switch14

.

Time (s)

Time (s)

Current (A)

Current (A)

(a)

(b)

19

2.1.3 Power Inverter

Switch mode dc to ac inverter are used to produce a sinusoidal ac output with

controllable magnitude and frequency. There are two main types of switch mode

inverters; voltage source inverters and current source inverters5. Voltage source inverters

can further be divided into the following categories:

a) Pulse width modulated inverters: here the voltage magnitude and frequency is

controlled by pulse width modulation of the inverter switches

b) Square wave inverters: here only the frequency of the output voltage can be

controlled. The output voltage wave

2.1.3.1 Topology Of The Conventional Inverter

The conventional single phase inverter (full bridge) utilizes four switches and four diodes

as shown in Fig 2.11. The switches can be any switching power electronic device. Fig 2.2

shows the single phase inverter topology with outputs Vr and a bus voltage of Vo. The

ideal switches facilitate the explanation of the generation of the control signals. The

diodes across each switch are necessary when driving inductive loads. The diodes carry

regenerative currents at times when the current direction in an inductive load and the

applied voltage have opposite polarity. The output Vr switches between –Vo and Vo.

Fig 2.11 Basic DC/AC inverter

20

2.1.3.2 Generation Of Pulse Width Modulation Signals

A block diagram for the generation of PWM signals is shown in Fig 2.12. The control

input is the desired waveform characteristic to be seen at the output (SINE.OUT).

Usually, this is a sine wave of fixed frequency with a normalized amplitude. The

repetitive waveform input is a triangle wave (TRIANG1.OUT) with a frequency

considerably higher than the frequency of the control signal. The triangle wave thus

becomes a carrier frequency for the control signal.

The comparator operates on two conditions: sine.out< triang1.out and sine.out>

triang1.out as shown in Fig 2.12a. When sine.out< triang1.out, the output of the

comparator (Fig 2.12b) is a logic high signal and the switches S1 and S4 are closed. For

sine.out> triang1.out, the output of the comparator is a logic low signal and the switches

S2 and S3 are closed (Fig 2.12c). The values of the logic signal from the comparator are

used to drive the switching elements. When in one of these states, the output voltage has

a value of either the positive DC bus or the negative DC bus.

Fig 2.12 a) Triangular and control waveforms b) PMW signal for S1 and S4

c) PMW signal for S2 and S3

21

2.2 Portunus Simulation

To ensure stability, power quality, and reliability, each new system should be simulated

before it is implemented in the field. The simulation is intended to confirm that a

particular control the results in the desired system or to reveal necessary design

modifications, or both. Using the Portunus simulation environment, an electronic power

converter system consisting of the rectifier, buck converter, inverter and their

corresponding control units was designed. With a library of the power electronic modules

available, it is easy to set up a particular system configuration.

The Portunus software is a vital circuit simulation environment that allows rapid testing

of parameters and calculation jobs within a broad range of applications. It is a coupled

system simulator which allows both analogue and digital components within a most user

friendly interface. Portunus has the flexibility to incorporate user-defined components

into the system. These components can be created using C++ programs, sub-sheets, non-

linear look-up tables, or direct imports of SPICE or VHDL-AMS models8.

Portunus only generates theoretical circuit output values which would only be observed

under ideal conditions therefore Portunus will be used as a guide for the buck converter

design and the comparison of laboratory experiments with simulated results.

In this project, the tools that Protunus Simulation Software offers for simulating and

designing energy systems that include power converters that can also comprise of a

rectifier, a DC bus, a Buck converter, and an inverter is emphasized. However the

microcontrollers for the buck converter and the DC-AC inverter will be simulated with

the use of ideal sources that will duplicate each controller’s desired output waveform.

2.3 Graphic User Interface

The Graphical User Interface is developed as the front end application to the FCIV

microcontroller using Visual Basic. The user can specify the kind of control and the

22

values of components functions. In the program the parameters of the equivalent circuit

can be entered on the circuit diagram.

The programming environment for the FCIV controller utilizes a R232 link to

communicate between the FCIV controller and GUI (on the developer’s computer). The

GUI interface displays all output parameters and the kind of control is specified by the

user. Buttons are provided to start and download control parameters into the FCIV

Controller.

Visual Basic is based on one of the world’s most widely known languages, Basic, and is

endowed with the ability to build applications for Microsoft Windows. In addition, the

language is appropriate for implementing Internet-based and World-Wide-Web based

applications, and it contains built-in features such as graphical user interface components,

file processing, linking to other Microsoft products such as Microsoft Word and

Microsoft Access, and database processing. The language is extensible so that

independent software vendors can provide component for a vast array of application

arenas15

.

23

CHAPTER THREE

3.1 Buck Converter Design

The voltage output is controlled by using a high frequency pulse-width-modulated

control (PWM) signal to drive the switching element (transistor or switch). Typically the

frequency of the pulse width modulated control signal is in the range of tens to hundreds

of kilo-Hz. There are two benefits, as frequency goes up, components become smaller,

lighter and cheaper. Another benefit is that the delay from input to output created by the

switching time is lower.

Typically, it is commended that the buck converter should be run in continuous mode for

expected loads.

First of all, the gain is stable. In continuous mode, the output Voltage (Vo) is

approximately set by input voltage (Vg) and the duty cycle only, regardless of load or

other component values. In discontinuous mode, Vo depends on Vg, Duty cycle, inductor

value, load and Frequency.

Secondly, for continuous and discontinuous modes, the frequency responses are

different. The transient response in continuous mode can change in discontinuous mode.

Thirdly the continuous mode operation tends to produce smaller ripple in output Voltage

Vo and interference (3)

.

3.2 Sizing Components

During component selection, each component is selected based on certain circuit

parameters.

24

Courtesy of practical design of Buck Converter by Johor Bahru

Fig. 3.1 Buck Converter With Component Rating

3.2.1 Inductor

Since the size of the inductor determines the operating mode of the buck converter,

inductor design plays an important role in buck converter design. The inductor functions

by taking energy from the electrical circuit storing it in a magnetic field and subsequently

returning this energy to the circuit4.

When the inductor is discharging3;

VL= -Vo = L diL /dt (3.1)

diL/dt = -Vo/L (3.2)

∆iLoff = -Vo/L * [∆toff]

∆iLoff = -Vo/L * [1-D]T (3.3)

When the inductor is charging,

VL= Vs -Vo = L diL /dt

diL/dt = [Vs –Vo]/L

∆iLon = (Vs-Vo/L )* [∆ton]

∆iLon = [Vs-Vo/L ]* DT (3.4)

25

Vs- Vo

Time

-Vo ton toff

iLMAX

iR ∆iL

iMIN

Fig 3.2 Inductor Voltage and Inductor current

Fig 3.2 shows the current and voltage waveform through the inductor.

ILMIN = IL – |∆iL|/2 = Vo/R - (1-D)Vo/ 2LF = Vo [1/R - (1-D)/ 2LF] (3.5)

ILMAX = IL + |∆iL|/2 = Vo/R + (1-D)Vo/ 2LF = Vo [1/R + (1-D)/ 2LF] (3.6)

3.2.1.1 Critical Inductance (LC)

The critical Inductance value is the minimum inductance value at which the inductor

current reaches Boundary conduction mode. Any inductance value lower than the critical

inductance causes the buck converter to operate in the discontinuous current conduction

mode. The inductor value is critical to maintaining current to the load while the switch is

off. It is necessary to determine the minimum inductance necessary to support the output

current of the Buck converter so that the load is supported under worst-case conditions of

output voltage and input current3.

Time

Current (A)

Voltage (V)

26

CURRENT

iL AT L = LC

Fig 3.3 Inductor Current at Critical Inductance

In order to obtain the critical inductance the maximum inductor current ripple ∆iL or

minimum percentage load requirement is specified.

ILMIN = 0 = IL – [|∆iL|/2 ] = Vo [1/R - (1-D)/ 2LF]

LC = (1-DMAX)RMAX / 2F (3.7)

RMAX = Vo/IMIN (3.8)

DMAX = duty cycle calculated at minimum input voltage

F= Frequency

Peak current through the inductor determines the inductor's required saturation-current

rating, which in turn dictates the approximate size of the inductor. Saturating the inductor

core decreases the converter efficiency, while increasing the temperatures of the inductor,

the MOSFET and the diode3. The peak current rating of the inductor is determined with

the maximum inductor current. The worse case minimum inductor current occurs at

maximum load.

3.2.2 Switch Rating

Transistors chosen for use in switching power supplies must have fast switching times

and should be able to withstand the voltage spikes produced by the inductor.

Voltage rating: With an ideal switch, the maximum switch voltage (V switchmax) is the

maximum voltage input3. But for a non ideal switch, V switchmax = Vinmax + VF where VF is

the maximum forward drop across the switch at maximum load current.

27

Current Rating: The switch current rating is calculated based on the average value of

switch current. During Ton , the inductor current is equal to switch current. During Toff

switch current is equal to zero.

ON OFF ON OFF t

(a)

iswitch

(b)

iDiode

t

T 2T

Fig 3.4 Current Waveform (a) Inductor Current (b) Switch Current (c) Diode

Current

Fig 3.4 shows the current wave forms through the diode, switch and diode.

Iswitch = (iLmin + iLmax) * ton / 2T (3.8)

Iswitch = [(iLmax - ∆iL )+ iLmax] * DT / 2T = [2iLmax - ∆iL ] * D / 2

Iswitch = [ iLmax - ∆iL /2] * D = iL * D

Iswitch > iL * Dmax (3.9)

28

3.2.3 Diode Rating

It is necessary that the diode should be able to turn off relatively fast. Diodes known as

the fast recovery diodes are used in these applications. The diodes average current ID is

equal to the load current times the portion of the time the diode is conducting Toff as

shown in Fig 3.5. The diode's forward-current specification must meet or exceed the

maximum output current3.

iDiode

OFF OFF

Fig 3.5 Diode current wave form

Idiode = (iLmin + iLmax) * toff / 2T

(3.10)

Idiode = [(iLmax - ∆iL )+ iLmax] * (1-D)T / 2T = [2iLmax - ∆iL ] * (1-D) / 2

Idiode = [ iLmax - ∆iL /2] * (1-D) = iL * (1-D)

Idiode> iL * (1-Dmin) (3.11)

The maximum reverse voltage on the diode is the maximum input voltage. The current

voltage ratings are low enough that a small Schottky diode or a fast recovery diode could

be used for this application.

Power dissipation is the limiting factor when choosing a diode. The worst-case average

power can be calculated as follows:

Pdiode = (1- Dmin) * iL * VD (3.12)

where VD is the voltage drop across the diode at the given output current IOMAX.

Time (s)

Current (A)

29

3.2.4 Output Capacitor Selection

The capacitor voltage should withstand the maximum output voltage. Ideally

Vcmax = VO + ∆Vo/2 (3.13)

Where ∆Vo = ripple voltage

VO = output voltage

Output capacitance is required to minimize the voltage overshoot and ripple present at the

output of a buck converter. Since switched power regulators are usually used in high

current, high-performance power supplies, the capacitor should be chosen for minimum

loss. Loss in a capacitor occurs because of its internal series resistance and inductance.

Capacitors for switched circuits are chosen on the basis of effective series resistance

(ESR). For very high performance power supplies, sometimes it is necessary to parallel

capacitors to get a low enough effective series resistance. The maximum allowed output-

voltage overshoot and ripple are sometimes specified at the time of design. Thus, to meet

the ripple specification for a buck converter circuit, an output capacitor with ample

capacitance and low ESR is included.

The output voltage ripple could be reduced by

Reducing the ESR by paralleling capacitors or using capacitors with lower ESR

The current ripple is reduced by increasing the circuit inductance or increasing the

switching Frequency

The current ripple in the inductor current flows through the capacitor leaving the

average flowing through the load1.

30

ic

ON OFF ON OFF

t

Fig 3.6 Capacitor Current Waveform

Fig 3.6 shows the capacitor current waveform.

Minimum output capacitance9

Q = ½ (T/2)(∆iL/2) = ∆iL/8F = [(Vo/L)(1-D)T] / 8F = (1-D)Vo/8LF2

Q= C*∆Vo

C= Q/∆Vo = [(1-D) Vo]/∆Vo 8LF2 = (3.14)

Vo/∆Vo = (3.15)

∆Vo = ripple Voltage

∆Vo/Vo = percentage Ripple

T/2

+Q

T

-Q

Ic

t

31

3.3 Open Loop Buck Converter Design

In the buck converter been designed, the circuit has the following specification:

Specification Value

Input Voltage (Vin) 32 – 64 V

Power Output (Po) 10 – 50 W

Switching Frequency (F) 20 kHz

Loading (R) 3 – 14 (Ω)

Output Voltage (Vout) 12 V

Time period of operation = T= Ton + Toff

T= 1/F = 1/20000 = 50 us

The Duty Cycle D is ;

Dmin = Vo/Vin(max) = 12/64 = 0.19

Dmax = Vo/Vin(min) = 12/32 = 0.375

3.3.1 Inductance

The minimum required inductance is

LC = (1-DMAX) RMAX / 2F

LC = (1-0.375)*14 / 2* 20000

LC = 2.1875 x 10-4

Henry

The Basic Buck circuit is simulated using the Portunus software using a period T = 50us

and pulse-width Duty Cycle of 0.19 (Fig 3.7). During Ton, the switch S1 drops to 0.01 Ω

connecting 64V (VIN) to L2. During Toff , the switch S1 pops open to 1 MΩ effectively

disconnecting voltage input from the inductor L2. R represents the load powered by the

Buck Converter.

With an inductance L equal to 0.3mH, the resulting inductor wave form is as shown in

Fig 3.8.

32

Fig 3.7 buck converter

t/s

50 u 100 u 150 u 200 u 250 u 300 u 350 u 400 u 450 u 500 u 550 u 600 u 650 u 700 u 750 u 800 u 850 u 900 u 950 u

0

500 m

1

1.5

2

L2.I

Fig 3.8 Inductor Current at L= 0.3mh

t/s

50 u 100 u 150 u 200 u 250 u 300 u 350 u 400 u 450 u 500 u 550 u 600 u 650 u 700 u 750 u 800 u 850 u 900 u 950 u

0

500 m

1

L2.I

Fig 3.9 Inductor Current at L= 0.7mh

The resulting critical inductance is 0.3mH. For the actual Buck Converter, an inductor of

size 0.7mH was selected, easily guaranteeing enough inductance to sustain continuous

current operation as shown in Fig 3.9. With the inductor size taken into consideration,

the 0.7mH inductor was designed with the following parameters:

Peak winding current Imax (A) 5

Inductance L (H) 0.0007

33

Winding fill factor Kµ 0.3

Core maximum flux density Bmax(T) 0.5

Air gap Lg (m) = [µ0LI2max / B

2max Ae ] * 10

4 (3.16)

With µ0 = 4*π 10-7

AL is equal to the inductance, in mH, obtained with a winding of 1000 turns.

AL = 10 B2max Ae

2 / L I

2max (3.17)

L = AL N2 10

-9 (Henries)

(3.18)

N = √( L/ AL 10-9

)

(3.19)

Where N = number of turns

Using Equations 3.15 – 3.18, the following results were obtained(16,17,18,19)

.

CORE AC MLT WA AL N Lg

ETD 29

0.76 5.33 0.903 82.51 93 1.16

ETD 34 0.97 6.00 1.23 134.41 73 0.91

ETD 39 1.25 6.86 1.74 223.21 56 0.7

ETD 44 1.73 7.62 2.14 427.56 41 0.51

Table 3.1 inductor cores and Corresponding Parameters

Where

Ae = Effective Core Area (cm2)

MLT = Mean Turn Area (cm)

WA = Winding Area (cm2)

Lg = Air gap (mm)

Using the ETD 39, the following parameters were obtained using

34

Aw= Kµ WA / N (3.20)

Where Aw = Bare copper Area

A wire with bare copper area AW less than or equal to this value is selected using the

metric Wire Gauge table is included in Appendix D.

R= ρN(MLT)/ Aww

Where Aww = bare copper area of actual copper used

Ρ = resistivity of copper = 1.724 * 10-6

Ω-cm

The resulting Inductor Design Parameter is shown in Table 3.2.

Type of Core ETD 39

Number of Turns(n) 64

Air Gap 1mm

Wire Bare Area (metric format) 0.91186 mm

Wire Bare Area (Aww) 6.5 x 10 -3

cm2

Winding resistance R(Ω) 0.102

Table 3.2 Inductor Design parameters

3.3.2 Capacitance

The key factor in determining the size of the capacitor is the amount of ripple voltage

desired. Specifically, it is preferable to minimize ripple voltage. A larger capacitor leads

to smaller ripple voltage. It was decided for this thesis that the ripple voltage, defined as

ΔVo /Vo is about 0.1%

Solving for the capacitor size using equation 3.14 yields

C= = = 362 microfarad

A Portunus Model is simulated using an inductance of 0.7mH and capacitance of 362uF

as shown in Fig 3.10

35

t/s


0

10

20

L2.I

R1.V

Fig 3.10 Output voltage and inductor current at L= 0.7mH and C= 362µF

t/s


0

10

20

L2.I

R1.V

Fig 3.11 Output voltage (R1.V) and inductor current (L2.I)at L= 0.7mH and C=

1000µF

The actual capacitor chosen for this thesis was 1000uF as shown in Fig 3.11. When

substituted into equation 3.15 this value yields a peak-to-peak ripple voltage of 0.036 %.

3.3.3 Diode rating

From Equation 3.11, the diode current rating > 4 * (1-0.1875) = 3.25A

Diode reverse voltage rating = 64V

The diode chosen for the actual buck converter was a Fast Soft Recovery Diode, model

20ETF04PbF, manufactured by Vishay. Specification sheets on this device are included

as Appendix A. This device is rated for 600V @ 20 amps. Most importantly, the diode

reverse recovery time is 60ns, which is 833 times less than the period of the 20 kHz

switching frequency.

3.3.4 Switch

For the current rating, from equation 3.8, the current rating of the switch should be

greater than 4*0.375= 1.5A. The maximum voltage rating is the maximum input voltage

that is 64V.

36

A 600V, SMPS Series N-Channel IGBT with Anti-Parallel Hyper-fast Diode was chosen

as the switch. The complete description of this component is found in Appendix B.

Fig 3.12 – 14 below show the waveforms obtained with the switching model simulation

when using the actual buck component parameters.

t/s


0

5

10

15

20

25R1.V

Fig 3.12 Voltage Output

t/s


0

5

10

15

L2.I

Fig 3.13 inductor current

t/s


0

500 m

1

1.5

R1.I

Fig 3.14 Output current

3.4 Closed Loop Buck Converter

Here control is introduced into the buck converter circuit. The feedback circuit monitors

the output voltage and compares it with a reference voltage, which is set electronically to

the desired output. If there is an error in the output voltage, the feedback circuit is

employed to varying the duty cycle in order to bring the output voltage as close as

possible to the reference voltage.

37

This control is necessary because input voltage variations and load variations can cause

the output voltage to change. This control is carried out by the FCIV (flexible controller

integrated test platform) controller as shown in Fig 3.15.

Fig 3.15 closed loop buck converter

3.4.1 Control Topology

Fig 3.16 Closed Loop Buck Control Topology

3.4.1.1 Error Amplifier

The essential part of the automatic control is the error amplifier which measures how

close the voltage output is to the reference voltage. The measurement of error is simple

the difference between voltage output and the reference voltage5.

PWM OUT

SAW TOOTH VOLTAGE SOURCE

BUCK CONVERTER

ERROR

AMP.

A

REFERENCE VOLTAGE

CO

MP

AR

ATO

R

Carried out in the

FCIV Controller

38

Verror= Vref - Vo

If Verror is positive , the duty cycle is increased and if Verror is negative then the duty cycle

is decreased and if Verror is zero then the current duty cycle is maintained.

3.4.1.2 Pulse width Modulation

In order to obtain the PWM signal, the saw tooth waveform Vsaw is compared with the

Verror signal. When Verror is greater than Vsaw then the output from the comparator is zero

and when Verror is less than Vsaw then the output from the comparator is zero. Thus the

duty cycle of the PWM output signal is proportional to the Error Voltage.

Portunus simulation of closed loop buck converter

Fig 3.17 Closed Loop Buck Converter and Open Loop Buck Converter

The closed loop buck converter and the open loop buck converter are simulated using

Portunus as shown in Fig 3.17.

39

t/s

500 u 1 m 1.5 m 2 m 2.5 m 3 m 3.5 m 4 m 4.5 m 5 m 5.5 m 6 m 6.5 m 7 m 7.5 m 8 m 8.5 m 9 m 9.5 m

0

-5

5

R7.V

PWMD2

Fig 3.18 Error voltage and PWM input signal of the closed loop buck converter

t/s

2 m 4 m 6 m 8 m 10 m 12 m 14 m 16 m 18 m 20 m 22 m 24 m 26 m 28 m 30 m 32 m 34 m 36 m 38 m 40 m 42 m 44 m 46 m 48 m

0

10

20

30

VM1.V

R1.V

Fig 3.19 Input voltage (VMI.1) and output voltage (R1.V) of the closed loop buck

converter

t/s

2 m 4 m 6 m 8 m 10 m 12 m 14 m 16 m 18 m 20 m 22 m 24 m 26 m 28 m 30 m 32 m 34 m 36 m 38 m 40 m 42 m 44 m 46 m 48 m

0

10

20

30

VM1.V

R1.V

Fig 3.20 Input Voltage (VMI.1) and output voltage (R1.V) of the open loop buck

converter


0

5

10

15

20

25

R1.V

R9.V

Fig 3.21 Closed Loop Converter Output (R1.V) and Open Loop Output (R9.V) with

Voltage input of 32V

From comparing the wave forms in Fig 3.19 and 3.20, it can be seen that the output of

open loop buck converter varies with variation of the input voltage.

40

3.5 Graphic User Interface

The user interface to the FCIV controller is developed using Visual Basic 2008. The goal

of the user interface is to make the user interaction with the FCIV controller as easy as

possible.

Here panels are provided in order to drive the buck converter in either the open loop or

closed loop operation. Circuit parameters are downloaded into the FCIV control with the

use of text boxes shown in Fig 3.18 and Fig 3.19.

Fig 3.22 Open Loop Simulation panel.

41

Fig 3.23 Closed-loop Simulation Panel

3.5.1 Input Parameters

Ki and Kp: these are buck gain parameters which are used in the closed loop buck

control carried out by the flexible controller integrated platform.

Duty Cycle: This is an open loop input parameter which is used to control the ON/OFF

position of the Buck converter switch.

Frequency: this controls the output frequency of the inverter output voltage.

42

Modulation Index : this controls the output waveform of the inverter output waveform.

3.5.2 Output Parameters

The buck output and the generator output are output parameters obtained from the FCIV.

The specific steps taken during the interaction between the user interface and the FCIV

controller when data is been inputted by the user as shown Fig3.24.

Fig 3.24 User Interface – Controller Interaction

Some back calculations are performed in order to recalculate design parameters after

standardization. The source code for the software developed using visual basic is

included in appendix C.

Stop controller

Change parameters

Set mode

Start controller

Send parameters

MODE OF BUCK OPERATION

USER

Send buck output

INPUT PARAMETERS

CONFIG

START

FLEXIBLE

CONTROLLER

INTEGRATED

PLATFORM

STOP

BUCK OUTPUT

43

CHAPTER FOUR

4.1 Simulation Results And Measured Experimental Results

In order to verify the theoretical models, experiments using the designed Buck Converter

and the FCIV controller as the switch controller was using on the output of the generator

rig as shown in Fig 4.1. The results presented in tables and graphs are obtained from;

i. Simulation using Portunus

ii. Experimental Results from the Experimental set up

iii. Numerical calculations

Fig.4.1 Generator Dynamometer

44

4.1.1 Generator No Load Testing

Power Rating: 0.18 kW

Generator Speed (rpm) Generator voltage

100 4.5

200 9.5

300 14

400 18.8

500 23.8

600 28.2

700 33

800 37.8

900 42.5

1000 49.7

1100 52.3

1200 57.1

1300 61.7

1400 66.6

1500 70.7

Table 4.1 Generator Output voltage with corresponding speed.

Fig.4.2 Variation of generation voltage verses speed

The generator voltage output and frequency increases with speed as shown in Fig 4.2.

The generator output voltage waveform is not perfectly sinusoidal as shown in Fig 4.3.

The voltage waveform was fed into the Portunus rectifier model resulting in results

shown in Fig 4.4.

45

Fig. 4.3 Generator Voltage Output at 500rpm

t/s

5 m 10 m 15 m 20 m 25 m 30 m 35 m 40 m 45 m 50 m 55 m 60 m 65 m 70 m 75 m 80 m

0

-10

-20

10

20

LOOKUP1.OUT

LOOKUP2.OUT

LOOKUP3.OUT

Fig 4.4 Three Phase Voltage Output from Portunus Generator Model

4.1.2 Rectifier Testing and Simulation

When the generator output is rectified with a three phase rectifier and the generator

torque and output DC voltage is measure for a generator speed range of 500 – 1000 rpm.

SPEED (RPM) BIN(V) TORQUE

500 31.9 0.042

700 44.5 0.047

900 57.8 0.05

1000 64 0.05

Table 4.2 Variation of generator speed with DC Voltage output

46

Fig 4.5: Rectifier output without a Capacitor (a) using Portunus simulation (b)

experimental result (c) Simulation and experimental results

Using a capacitance of 1000uF as a filter, the Potunus model as shown in Fig 4.6 outputs

the waveform shown in Fig 4.7

47

Fig 4.6 Portunus Rectifier Model

t/s

5 m 10 m 15 m 20 m 25 m 30 m 35 m 40 m 45 m 50 m 55 m 60 m 65 m 70 m 75 m 80 m

10

20

30

R1.V

Fig 4.7 Rectifier output with 1000uF Capacitor

4.1.3 Buck Converter Testing and Simulation

The designed Buck Converter is connected to a DC power supply and the FCIV

controller where the output voltages are obtained at different duty Cycles. The Open

Loop Buck converter is modeled using Portunus simulation (Fig 4.7) and measurements

were obtained. The measurements are tabled and plotted below (Fig. 4.8- 4.11).

Fig 4.8 Rectifier – Open Loop Buck converter Portunus Model

48

Load =50W Input Voltage = 30V

Experimental results Simulation results

PWM (%) Buck Voltage O/P Buck Voltage O/P

10 1.8 2.18

20 4.4 5.6

25 5.7 7.06

30 7.0 8.5

35 8.3 9.96

40 9.6 11.4

45 10.8 12.86

50 12.1 13.7

Table 4.3 : Variation of Buck Output Voltage with input voltage of 30V

Fig.4.9 Buck Output at voltage input of 30V and power output of 50W

49

Loading =50W Input Voltage = 60V



5 1.5 2.7

10 4.0 5.28

15 6.5 9.5

20 9.0 12.57

25 11.5 15.6

26 11.9 16.2

27 12.4 16.8

Table 4.4 : Variation of Buck Output Voltage with input voltage of 60V


50

Load =10W Input Voltage = 30V



10 2.0 2.18

20 4.8 5.76

25 6.2 7.25

30 7.6 8.7

40 10.4 11.7

45 11.8 13.1

46 12.1 14

Table 4.5: Variation of Buck Output Voltage with input voltage of 30V


51

Load =10W Voltage = 60V



5 1.8 2.78

10 4.5 5.15

20 10 12.3

21 10.6 12.9

23 11.7 14

24 12.2 15

Table 4.6: Variation of Buck Output Voltage with input voltage of 60V


From Fig 4.5 - 4.8 the simulated vary from the experimental results due to the fact that

the simulation makes use of ideal components. Voltage drop across each component need

to be taken into consideration.

The buck converter was then tested with the actual PM Generator and Rectifier as an

input and the above measurements are repeated.

52

SPEED(rpm) TORQUE(Nm) Bin (V) Bout(V) B(out I) DC

500 0.29 27.2 12 0.87 50

500 0.34 26.5 11.5 1.07 50

500 0.41 25.6 11 1.3 50

500 0.5 24.3 10.1 1.69 50

Table 4.7 Buck Output at varying Power Output (10W- 50W) with generator speed

500 rpm

Power Input = torque *speed/60 *2π (4.1)

Power Output = Bout(V) * Bout(I) (4.2)

Efficiency = Power Output/Power Input (4.3)

At maximum loading, efficiency = 10.44/15.18 = 69%


750 0.22 41.4 12.4 0.9 34

750 0.29 40.4 11.9 1.24 34

750 0.36 39.2 11.4 1.6 34

750 0.48 37.4 10.4 2.3 34


750 rpm



1000 0.17 60.6 12.2 0.86 23

1000 0.2 59.9 11.9 1.17 23

1000 0.26 58.8 11.4 1.6 23

1000 0.38 56.6 10.5 2.6 23


1000 rpm

53


From the tables above the efficiency of the power converter rig i.e. Buck Converter +

Rectifier shows that the efficiency drops with increase in speed.

4.1.4 Inverter Simulation

The inverter was tested with the Buck converter and the FCIV controller. The resulting

current wave form was distorted due to current drop in the switches. The Portunus

inverter model is as shown below.

Fig. 4.13 Inverter Model

t/s

50 m 100 m 150 m 200 m 250 m 300 m 350 m 400 m 450 m 500 m 550 m 600 m 650 m

0

-2.5

2.5

5

R1.V

Fig 4.14 Inverter Output

54

Fig 4.15 Experimental Setup

55

CHAPTER FIVE

5.1 Conclusion

This thesis has presented the design of the Buck Converter and its implementation in the

power converter Unit. The buck converter was designed to operate with the input range

of 32-64V DC. A load range of 3-14 was selected that would result in a power output

range of 10-50W. The control of the buck converter is carried out by the by the flexible

controller integrated platform developed in the SPEED laboratory. A user end interface to

the FCIV controller using visual basic programming was designed. A complete model

comprising of a rectifier, buck converter and inverter was created using the Portunus

simulation software.

Due to equipment limitation and the prototype nature of the buck converter the efficiency

67% was obtained.

Fig. 5.1 Efficiency Verses Speed of Generator

Fig 5.1 illustrates the efficiencies obtained at different speeds. This is due to the losses

due to Resistance of the switch, Diode forward voltage drop, Inductor winding resistance,

Capacitor equivalent resistance.

56

When the Buck Converter is operated in closed loop, the losses are not considered as it

does not affect the buck converter output as the control loop compensates for the voltage

drop by increasing the duty cycle.

57

REFERENCE

[1] Donald Schelle and Jorge Castorena. Maxim Integrated Products. Retrieved from

Maxim Integrated Products website:

http://powerelectronics.com/power_systems/dc_dc_converters/power_buckconverter_

design_demystif

[2] AWG to Metric Conversion table . Retrieved from Engineering ToolBox website:

http://www.engineeringtoolbox.com/awg-wire-gauge-d_731.html

[3] The practical design of a buck converter by Johor Bahru. Retrieved from IEEE

Website: http://ewh.ieee.org/r10/malaysia/ie_ia_pel/pecon2008/akhtar_tutorial.pdf

[4] Bennett, J. C. (2006). Practical computer analysis of switch mode power supplies.

CRC Press.

[5] Buck Conver Basics. Retrieved from eCircuit Center website:

www.ecircuitcenter.com/Circuits/smps_buck/smps_buck.html

[6] Unitode Magnetics Design Handbook .

[7] 600 Watt Pure Sine Wave Inverter. Retrieved from

http://www.donrowe.com/inverters/puresine 600.html

[8] Portunus Information. Retrieved from Cedrat Groupe Website:

http://www.cedrat.com/en/software-software-solutions/portunus.html

[9] Introduction to power supplies . Retrieved from National Semiconductor website:

http://www.national.com/an/AN/AN-556.pdf

[10] Lee, Yim. (1993). Computer-aided analysis and design of switch mode power

supplies. CRC Press.

[11] Mohan,Undeland and Robbins. (2007). Power electronics: converters, applications

and design. Wiley India.

[12] Raymond A. Mack, J. (2005). Demystifying Switching Power Supplies . Newnes.

[13] Operation Of A 3-Phase Fully-Controlled Rectifier. Retrieved from university of

Sydney website: http://services.eng.uts.edu.au/~venkat/pe_html/ch05s1/ch05s1p1.htm

[14] Step down: SMPS Buck Converter Ideal Circuit. Retrieved from university of Sydney

website: http://services.eng.uts.edu.au/~venkat/pe_html/ch07s1/ch07s1p1.htm#intro

58

[15] Robert Warren Erickson, D. M. (2001). Fundamentals of Power Electronics.

Springer.

[16] ETD39 Datasheet. Retrieved from Fexxocube website:

http://www.ferroxcube.com/prod/assets/etd39.pdf







[20] Feucht, D. L. (n.d.). Practical Design of a Buck Converter. AnalogZONE .

[21] Understanding variable output characteristics of wind Power. Retrieved from wind

energy the facts.org website: http://www.wind-energy-the-

facts.org/_includes/print.php?lg=en&cmp_id=48&safe_mode= 8/13/2009





59

APPENDIX A

60

APPENDIX B

61

APPENDIX C

Public Class Simulation_Form

Dim bytLength As Byte

Dim bytPackage11(10) As Byte, bytPackage8(7) As Byte

Dim bytEcho11(10) As Byte, bytEcho8(7) As Byte

Dim vntwarning As Object

Dim blnComunication As Boolean

Dim bytStatusInfo As Byte

Dim intStatusInfo As Integer

Dim varStatusInfo As Object

Dim intRun As Integer

Dim intDCF As Integer

Dim intVF As Integer

Dim intKpF As Integer

Dim intKiF As Integer

Dim lngDC As Long

Dim intDC As Integer

Dim intVref As Integer

Dim intKp As Integer

Dim intKi As Integer

Dim intBM As Integer

Dim intFrequency As Integer

Dim intFF As Integer

Dim intMI As Integer

Dim intMIF As Integer

Private Sub cmdDL_Click()

intKp = txtKP.Text

intKi = txtKI.Text

intMI = txtModulationIndex.Text

End Sub

'Sequence to carry out Serial Communications via RS232 Port

'------------------------------------------------------------------

---------------------------------------------

Public Sub Comunication(ByVal bytLength As Byte, ByRef bytPackage()

As Byte)

Dim intCount As Integer

' Used to count read/write buffers through TX/RX arrays

Dim varWarning As VariantType

' Used to Launch Error Warnings

Dim intVerify As Integer

' Used to wait check message is recieved.

Dim intError As Integer

' Used to timeout the waiting for a message to be recieved

intError = 0

62

intCount = 11

Try

MSComm1.Open()

Catch ex As Exception

'SetButtonForStop()

varWarning = MsgBox("Unable to open Comm port ",

MsgBoxStyle.Critical, "Communications Error")

Return

End Try

'Open Serial Port

Try

MSComm1.Write(bytPackage, 0, intCount)

' Write bytPackage to the output buffer of the serial port

Do Until intVerify = intCount

If intVerify = intCount Then

' wait until 11 bytes are recieved

Exit Do

End If

intVerify = MSComm1.BytesToRead

intError += 1

If intError = 500 Then

Throw New ApplicationException("Timeout")

' if recieve operation times out then throw an exception

End If

Threading.Thread.Sleep(1)

' delay a millisecond per loop (500ms delay total)

Loop

Catch writeExc As Exception

' Warning information when communication fails

varWarning = MsgBox("The Interface has not been able to " &

_

"send data to the FCIV, please check the status of the " &

_

"serial Port", MsgBoxStyle.Critical, "Communications

Error")

varWarning = MsgBox("The FC4 interface will now close, " &

_

"please re-check all connections", _

MsgBoxStyle.Critical, "Interface Shutdown")

Close()

' Close the programme if the communications fail

End Try

Try

' MSComm1.Read(bytRecieve, 0, intCount)

' Read the serial port input buffer and store in bytReceive

Catch readException As System.TimeoutException

' If the read operation times out show warning

varWarning = MsgBox("The Interface has not recieved data "

& _

"from FCIV, check serial connection", _

63

MsgBoxStyle.Critical, "Communications Error")

varWarning = MsgBox("The FC4 interface will now close, " &

_

"please re-check all connections", _

MsgBoxStyle.Critical, "Interface Shutdown")

Close()

' Close programme if the communications fail

End Try

MSComm1.Close()

' Close the Serial Port

End Sub

Private Sub btn_configure_Click(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles btn_configure.Click

If ValidateForm() Then

'Enable buttons after connecting successfully to Controller

via the port

btn_run.Enabled = True

btn_run.BackColor = Color.FromArgb(0, 192, 0) 'green

btn_configure.Enabled = True

' intRun = 1

End If

'Package to send Buck Mode Command

bytLength = 11

Call BuildPackage(bytLength, 18, 108, 0, _

CByte(intBM), 0)

Call Comunication(bytLength, bytPackage11)

If intFF = 1 Then

intFrequency = txtFrequency.Text / 2

'Package to send Frequency Command

bytLength = 11


CByte(intFrequency), 0)


intFF = 0

End If

If intMIF = 1 Then

'Package to send Mod Index Command

bytLength = 11

intMI = txtModulationIndex.Text


CByte(intMI), 0)


intMIF = 0

End If

If intDCF = 1 Then

'Package to send Duty Cycle Command

bytLength = 11

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Call BuildPackage(bytLength, 18, 104, 0, CByte(Fix(intDC /

256)), CByte(intDC Mod 256))


intDCF = 0

End If

If intVF = 1 Then

'Package to send Vref Command

intVref = txtRefVoltage.Text

bytLength = 11


CByte(Fix(intVref / 256)), CByte(intVref

Mod 256))


intVF = 0

End If

If intKpF = 1 Then

'Package to send Kp Command

bytLength = 11

intKp = txtKP.Text


CByte(Fix(intKp / 256)), CByte(intKp Mod

256))


intKpF = 0

End If

If intKiF = 1 Then

'Package to send Ki Command

intKi = txtKI.Text

bytLength = 11


CByte(Fix(intKi / 256)), CByte(intKi Mod

256))


intKiF = 0

End If

End Sub

Private Sub btn_stop_Click(ByVal sender As System.Object, ByVal e

As System.EventArgs)

End Sub

Private Sub Label11_Click(ByVal sender As System.Object, ByVal e As

System.EventArgs)

End Sub

Private Sub GroupBox4_Enter(ByVal sender As System.Object, ByVal e

As System.EventArgs) Handles GroupBox4.Enter

End Sub

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Private Sub txt_gen_voltage_TextChanged(ByVal sender As

System.Object, ByVal e As System.EventArgs) Handles

txt_gen_voltage.TextChanged

End Sub

Private Sub RadioButton1_CheckedChanged(ByVal sender As


rdbCloseLoop.CheckedChanged

If rdbCloseLoop.Checked = True Then txtDutyCycle.Enabled =

False

txtKP.Enabled = True

txtKI.Enabled = True

txtRefVoltage.Enabled = True

intBM = 2 'closed loop

End Sub

Private Sub RadioButton2_CheckedChanged(ByVal sender As


rdbOpenLoop.CheckedChanged

If rdbOpenLoop.Checked = True Then txtDutyCycle.Enabled = True

txtKP.Enabled = False

txtKI.Enabled = False

txtRefVoltage.Enabled = False

intBM = 1 'open loop

End Sub

Private Sub Label10_Click(ByVal sender As System.Object, ByVal e As

System.EventArgs) Handles Label10.Click

End Sub

Private Sub GroupBox1_Enter(ByVal sender As System.Object, ByVal e

As System.EventArgs) Handles GroupBox1.Enter

End Sub

Private Sub Label11_Click_1(ByVal sender As System.Object, ByVal e

As System.EventArgs) Handles Label11.Click

End Sub

Private Sub btn_run_stop_Click(ByVal sender As System.Object, ByVal

e As System.EventArgs) Handles btn_run.Click

If intRun = 1 Then

btn_run.BackColor = Color.FromArgb(0, 192, 0) 'green

intRun = 0

btn_run.Text = "RUN"

btn_run.Enabled = False

btn_configure.Enabled = True

bytLength = 11

Call BuildPackage(bytLength, 18, 103, intRun, intRun,

intRun)


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Else

btn_run.BackColor = Color.FromArgb(192, 0, 0) 'red

intRun = 1

btn_run.Text = "STOP"

bytLength = 11

Call BuildPackage(bytLength, 18, 103, intRun, intRun,

intRun)


End If

End Sub

Private Sub SetButtonsFor_op_control()

txtDutyCycle.Enabled = True




intRun = 0

intFrequency = 50

intMI = 100

intDC = 375

intVref = 1000

intKp = 20

intKi = 15

intFF = 0

intMIF = 0

intDCF = 0

intVF = 0

intKpF = 0

intKiF = 0

'Package to send Frequency Command

bytLength = 11


CByte(intFrequency), 0)


'Package to send Mod Index Command

bytLength = 11


CByte(intMI), 0)


'Package to send Duty Cycle Command

bytLength = 11


CByte(Fix(intDC / 256)), CByte(intDC Mod 256))


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'Package to send Vref Command

bytLength = 11


CByte(Fix(intVref / 256)), CByte(intVref Mod

256))


'Package to send Kp Command

bytLength = 11


CByte(Fix(intKp / 256)), CByte(intKp Mod 256))


'Package to send Ki Command

bytLength = 11


CByte(Fix(intKi / 256)), CByte(intKi Mod 256))


End Sub

Public Sub BuildPackage(ByVal intLength As Integer, ByVal bytCmd As

Byte, ByVal bytFunc1 As Byte, ByVal bytFunc2 As Byte, _

ByVal bytMsb As Byte, ByVal bytLsb As Byte)

Dim intCount As Integer

Select Case intLength

Case 8

bytPackage8(0) = 8 'No. bytes lsb

bytPackage8(1) = 0 'No. bytes msb

bytPackage8(2) = 1 'Destination

bytPackage8(3) = 64 'Source

bytPackage8(4) = bytCmd 'Select Test Function

Command

bytPackage8(5) = bytFunc1 'data 1, test function

bytPackage8(6) = bytFunc2 'data 2

bytPackage8(7) = bytPackage8(0) Xor bytPackage8(1)

'checksum

For intCount = 2 To 6 ' XOR of all bytes

excluding the checksum

bytPackage8(7) = bytPackage8(7) Xor

bytPackage8(intCount)

Next intCount

Case 11

bytPackage11(0) = 11 'No. bytes lsb

bytPackage11(1) = 0 'No. bytes msb

bytPackage11(2) = 1 'Destination

bytPackage11(3) = 64 'Source

bytPackage11(4) = bytCmd 'Command

bytPackage11(5) = bytFunc1 'data 1, Parameter

Identifier (PI)

bytPackage11(6) = bytMsb 'data 2, msb

bytPackage11(7) = bytLsb 'data 3, lsb

bytPackage11(8) = 0 'data 4

bytPackage11(9) = 0 'data 5

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bytPackage11(10) = bytPackage11(0) Xor bytPackage11(1)

'checksum

For intCount = 2 To 9 ' XOR of all bytes

excluding the checksum

bytPackage11(10) = bytPackage11(10) Xor

bytPackage11(intCount)

Next intCount

End Select

Timer1.Enabled = True

End Sub

Private Sub optCL_Click()

txtDutyCycle.Enabled = False

txtKP.Enabled = True

txtKI.Enabled = True

txtRefVoltage.Enabled = True

intBM = 2


bytLength = 11


CByte(intBM), 0)


End Sub

Private Sub optOL_Click()

txtDutyCycle.Enabled = True




intBM = 1


bytLength = 11


CByte(intBM), 0)


End Sub

Private Sub txtDC_Change()

intDCF = 1

txtDutyCycle.ForeColor = Color.FromArgb(192, 0, 0)

End Sub

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Private Sub txtFreq_Change()

intFF = 1

txtFrequency.ForeColor = Color.FromArgb(192, 0, 0)

End Sub

Private Sub txtKi_Change()

intKiF = 1

txtKI.ForeColor = Color.FromArgb(192, 0, 0)

End Sub

Private Sub txtKp_Change()

intKpF = 1

txtKP.ForeColor = Color.FromArgb(192, 0, 0)

End Sub

Private Sub txtMI_Change()

intMIF = 1

txtModulationIndex.ForeColor = Color.FromArgb(192, 0, 0)

End Sub

Private Sub txtVref_Change()

intVF = 1

txtRefVoltage.ForeColor = Color.FromArgb(192, 0, 0)

End Sub

Private Function ValidateForm() As Boolean

If (rdbCloseLoop.Checked = True) Then

'KP validation

If (txtKP.Text.Trim() = "" Or intKp > 100) Then

MsgBox("kp cannot be blank or zero",

MsgBoxStyle.Exclamation, "kp")

txtKP.Focus()

Return False

End If

'KI validation

If (txtKI.Text.Trim() = "" Or intKi > 100 Or intKi > intKp)

Then

MsgBox("ki cannot be blank ", MsgBoxStyle.Exclamation,

"ki")

txtKI.Focus()

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Return False

End If

'Ref Voltage validation

If (txtRefVoltage.Text.Trim() = "" Or intVF > 2048) Then

MsgBox("Ref Voltage cannot be blank",

MsgBoxStyle.Exclamation, "Ref Voltage")

txtRefVoltage.Focus()

Return False

End If

ElseIf (rdbCloseLoop.Checked = False) Then

'Duty cycle validation

If (txtDutyCycle.Text.Trim() = "" Or intDC > 3750) Then

MsgBox("DutyCycle.Text cannot be blank or greater than

100", MsgBoxStyle.Exclamation, "DutyCycle")

txtDutyCycle.Focus()

Return False

End If

End If

If (txtModulationIndex.Text.Trim() = "" Or intMI > 100) Then

MsgBox("Modulation Index cannot be blank",

MsgBoxStyle.Exclamation, "Modulation Index")

txtModulationIndex.Focus()

Return False

End If

'frequecy validation

If (txtFrequency.Text.Trim() = "" Or txtFrequency.Text = "0")

Then

MsgBox("Frequency cannot be blank or zero",

MsgBoxStyle.Exclamation, "Frequency")

txtFrequency.Focus()

Return False

End If

Return True

End Function

Private Sub btn_run_EnabledChanged(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles btn_run.EnabledChanged

End Sub

Private Sub txtFrequency_TextChanged(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles txtFrequency.TextChanged

intFF = 1

End Sub

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As

System.EventArgs) Handles Timer1.Tick

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End Sub

Private Sub txtDutyCycle_TextChanged(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles txtDutyCycle.TextChanged

intDCF = 1

lngDC = txtDutyCycle.Text * 3750

lngDC = lngDC / 100

intDC = lngDC

End Sub

Private Sub txtRefVoltage_TextChanged(ByVal sender As


txtRefVoltage.TextChanged

intVF = 1

End Sub

Private Sub txtKI_TextChanged(ByVal sender As System.Object, ByVal

e As System.EventArgs) Handles txtKI.TextChanged

intKiF = 1

End Sub

Private Sub txtKP_TextChanged(ByVal sender As System.Object, ByVal

e As System.EventArgs) Handles txtKP.TextChanged

intKpF = 1

End Sub

Private Sub Simulation_Form_Load(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles MyBase.Load

intRun = 0

End Sub

Private Sub txtModulationIndex_TextChanged(ByVal sender As


txtModulationIndex.TextChanged

intMIF = 1

End Sub

End Class

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APPENDIX D

design and implementation of a buck converter by kemjika ananaba

Documents

Transcript of design and implementation of a buck converter by kemjika ananaba