DESIGN ANALYSIS AND SIMULATION STUDY OF DC -Final Paper -running (Autosaved)

View with images and charts

Electrical and Electronic Engineering

Chapter 1

1.1 Overview

Over the years as the portable electronics industry progressed, different requirements evolved such as increased battery lifetime, small and cheap systems, brighter, full-color displays and a demand for increased talk-time in cellular phones. An ever increasing demand from power systems has placed power consumption at a premium. To keep up with these demands engineers have worked towards developing efficient conversion techniques and also have resulted in the subsequent formal growth of an interdisciplinary field of Power Electronics. However it comes as no surprise that this new field has offered challenges owing to the unique combination of two major disciplines of electrical engineering: electronics and power.

Generically speaking the use of a switch or switches for the purpose of power conversion can be regarded as an SMPS (switch mode power supply). A dc-dc converter can be considered as dc equivalent to an ac transformer with a continuously variable turn’s ratio.

A converter is not manufacturing power. Whatever comes at the output has to come only from input. Efficiency cannot be made equal to 100%, so input power is always somewhat larger than output power.

1.2 Application of DC-DC converters

DC-DC converters are used whenever we want to change DC electrical power efficiently from one voltage level to another. A few applications of interest of DC-DC converters are where 5V DC on a personal computer motherboard must be stepped down to 3V, 2V or less for one of the latest CPU chips; where 1.5V from a single cell must be stepped up to 5V or more, to operate electronic circuitry.

A power silicon device like micro-controllers or digital logic requires a different voltage than bias supplies or powering strings of LEDs. A system can very easily contain a combination of circuits that require different voltages.

DC-DC converters are widely used for traction motor control in electric automobiles, trolley cars, marine hoists, forklift trucks, and mine haulers. They provide smooth acceleration control, high efficiency, and fast dynamic response. DC-DC converters can be used in regenerative braking of dc motors to return energy back into the supply, and this feature results in energy savings for transportation systems with frequent stops. Dc converters are used in dc voltage regulators and also are used in conjunction with an inductor, to generate a dc current source, especially for the current source inverter.

The needs for such converters have risen due to the fact that transformers are unable to function on dc.

1.3 Different topologies

Dc converters can be used as switching mode regulators to convert a dc voltage, normally unregulated, to a regulated dc output voltage. The regulation is normally achieved by PWM at a fixed frequency and the switching driver is normally BJT, MOSFET, or IGBT.

The power regulator can be an inductor based, switch-mode power converter, a switched capacitor charge pump or a linear regulator. Each regulator has its own advantages and disadvantages, but it is the particular application requirements that determine which type of power regulator is best suited.

There are four basic topologies of switching-mode regulators:

Buck regulator Boost regulator Buck-boost regulator Cuk regulator

This project paper focuses specially on Buck and Boost regulator topologies. The boost is one of the fundamental switch-mode power topologies. The other being is the buck regulator. From these two topologies, all other topologies switch-mode power supply topologies are derived

1.4 Objective of the project

Get a clear idea on the working principles of Buck and Boost converters/regulators

Obtain performance parameter equations

Design analysis of these two converter through mathematical example

Create PSPICE circuit for simulating buck and boost converters

Obtain different output voltage curve with the change of input parameters

Discussion and evaluation of output graphs

Chapter 2

DC-DC converters

2.1 Buck converter

A Buck converter is a step down DC-DC converter consisting mainly of inductor and two switches (usually a transistor switch and a diode) for controlling inductor. It fluctuates between connection of inductor to source voltage to accumulate energy in inductor and then discharging the inductor’s energy to the load.

Fig 2.1: Basic Buck circuit When the switch pictured above is closed (i.e. On-state), the voltage across the inductor is VL = Vi − Vo. The current flowing through inductor linearly rises. The diode doesn’t allow current to flow through it, since it is reverse-biased by voltage V.

For Off Case (i.e. when switch pictured above is opened), diode is forward biased and voltage is VL = − Vo (neglecting drop across diode) across inductor. The inductor current which was rising in ON case now decreases.

Ideal circuit analysis

In a buck converter, the average output voltage Va is less than the input voltage, Vs.

The circuit diagram of a buck regulator has shown below and this is like a step-down converter.

Fig 2.2: Circuit diagram of a ideal buck regulator

Fig2.3: Circuit when switch closed (On-state)

The circuit operation can be divided into two modes. Mode 1 begins when transistor S is switched on at t = 0. The input current, which rises, flows through filter inductor L, filter capacitor C and load resistor R.

Fig 2.4: Circuit when switch is open (Off-state)

Mode 2 begins when transistor S is switched off at t = t1.

The freewheeling diode D conducts due to energy stored in the inductor; and the inductor current continues to flow through L, C, Load, and diode D. The inductor current falls until transistor S is switched on again in the next cycle.

The waveforms for voltage and current are shown in for continuous load current assuming that the current rises or falls linearly

Fig2.5: Voltage and Current waveforms of Buck converter

For a continuous current flow in the inductor L, it is assumed that the current rises and falls linearly. In

practical circuits, the switch has a finite, nonlinear resistance. Its effect can generally be negligible in most applications. Depending on the switching frequency, filter inductance, and capacitance, the inductor current could be discontinuous.

The voltage across the inductor L is,

= L

Assuming that the inductor current rises linearly form I1 to I2 in time t1,

Vs - Va = L = L (1.00)

or

t1 = (1.01)

and the inductor current falls linearly from I2 to I1 in time t2,

- Va = - L (1.02)

or

t2 = (1.03)

where = I2 - I1 is the peak-to-peak ripple current of the inductor L. Equating the value

of in Eqs. (1.00) and (1.02) gives

= =

Substituting t1 = KT and t2 = (1- K)T yields the average output voltage as

Va = Vs = KVs (1.04)

Assuming a lossless circuit Vs Is = Va Ia = K Vs Ia and the average input current Is = K Ia (1.05)

The switching period T can be expressed as

T = = t1 + t2 = + = (1.06)

which gives the peak-to-peak ripple current as

= (1.07)

or

(1.08)

Using Kirchhoff’s current law, we can write the inductor current as

=

If we assume that the load ripple current is very small and negligible, . The

average capacitor current, which flows into for t1/2 + t2 /2 = T/2, is

=

The capacitor voltage is expressed as

= + (t =0)

And the peak-to-peak ripple voltage of the capacitor is

Vc = - (t = 0) = = = (1.09)

Substituting the value of from Eq. (1.07) or (1.08) in Eq. (1.09) yields

= (1.2)

or

= (1.21)

Condition for continuous inductor current and capacitor voltage:

If is the average inductor current, the inductor ripple current

.

Using Eqs. (1.04) and (1.08), we get

Which gives the critical value of inductor as

(1.22)

If Vc is the average capacitor voltage, the capacitor ripple voltage Vc = 2 Va

Using Eqs. (1.04) and (1.21), we get

= 2 Va = 2 KVs

Which gives the critical value of the capacitor as,

2.2 Boost converter

A boost converter (step-up converter), as its name suggest step up the input DC voltage value and provides at output. This converter contains basically a diode, a transistor as switches and at least one energy storage element. Capacitors are generally added to output so as to perform the function of removing output voltage ripple and sometimes inductors are also combined with.

Fig 2.6: Basic Boost circuit

Its operation is mainly of two distinct states: During the ON period, Switch is made to close its contacts which results in increase of inductor current. During the OFF period, Switch is made to open and thus the only path for inductor current to flow is through the fly-back diode ‘D’ and the parallel combination of capacitor and load. This enables capacitor to transfer energy gained by it during ON period.

Ideal circuit analysis

In a boost regulator the output voltage is greater than the input voltage hence the name ‘boost’. A boost regulator using a power MOSFET is shown in Figure.

Fig 2.7: Circuit diagram of a ideal Boost regulator

The circuit operation can be divided into two modes.

Mode 1 begins when transistor S is switched on at t = 0. The current which rises flows through inductor L and transistor S.

Fig2.8: Circuit when switch is closed(On-state)

Mode 2 begins when transistor S is switched off at t= t1

Fig2.9: Circuit when switch is open (Off-state)

The current that was flowing through the transistor would no flow through L,C load and diode D. The inductor current falls until transistor S is turned on again in the next cycle. The energy stored in inductor L is transferred to the load.

The waveforms for voltage and current are shown in for continuous load current assuming that the current rises or falls linearly.

Fig2.10: Voltage and Current waveforms of Boost converter

Assuming that the inductor current rises linearly from I1 to I2 in time t1

Vs = L =

(2.01)

t1 =

(2.02)

and the inductor current falls in nearly form I2 to I2 in time t2

Vs = Va = -

(2.03)

t2 =

(2.04)

Where I2-I1 is the peak to peak ripple current of inductor L.

From Eqs. (2.01) and (2.03)

Substituting t1 = kT and t2 = (1-K)T yields the average output voltage.

Va= Vs (2.05)

Which gives,

(1-k) = (2.06)

Substituting k = t1/T = T1 f into Eq. (2.06) yields

t1= (2.07)

Assuming a lossless circuit VsIs = VaIa = VSlal(1-k) and the average input current is

ls =

(2.08)

The switching period T can be found from

T= + = =

(2.09)

and gives the peak to peak ripple current.

=

(2.10)

or

= (2.11)

When the transistor is on, the capacitor supplies the load current for t = t1. The average capacitor current during time t1 is lc = la and the peak to peak ripple voltage of the capacitor is

= dt = = (2.12)

Substituting t1 = (Va- Vs)/(Vaf) from Eq. (5.64) gives

= (2.13)

Or

= (2.14)

Condition for continuous inductor current and capacitor voltage

If IL is the average inductor current the inductor ripple current 2IL .

Using Eqs. (2.05) and (2.11)

= 2IL = 2Ia =

Which gives the critical value of the inductor Lc as

Lc = L=

(2.15)

If Vc is the average capacitor voltage, the capacitor ripple voltage Vc = 2Va Using Eq. (2.14), we get

= 2Va = 2IaR

Which gives the critical value of the capacitor Cc as

Cc = C=

A boost regulator can step up the output voltage without a transformer. Due to a single transistor, it has a high efficiency. The input current is continuous. However a high peak current has to flow through the power transistor. The output voltage is very sensitive to changes in duty cycle k and it might be difficult to stabilize the regulator. The average output current is less than the average inductor current by a factor of (1-k), and a much higher rms current would flow through the filter capacitor, resulting in the use of a larger filter capacitor and a larger inductor than those of a buck regulator

Chapter 3

Design analysis of DC-DC converters

3.1 Performance parameters

There are some basic performance parameters which decide the output characteristics of the DC-DC converter.

These parameters should be well understood before designing an ideal dc-dc converter.

Operating frequency

The operating frequency determines the performance of the switch. Switching frequency selection is typically determined by efficiency requirements.There is now a growing trend in research work and new power supply designs in increasing the switching frequencies. The higher is the switching frequency, the smaller the physical size and component value.

At higher frequencies the switching losses in the MOSFET increase, and therefore reduce the overall efficiency of the circuit.

At lower frequencies the required output capacitance and inductor size increases, and the volumetric efficiency of the supply degrades.

The trade-off between size and efficiency has to be evaluated very carefully.

Inductor Selection

The function of the inductor is to limit the current slew rate (limit the current in rush) through the power switch when the circuit is ON. The current through the inductor cannot change suddenly. When the current through an inductor tends to fall, the inductor tends to maintain the current by acting as a source. This limits the otherwise high-peak current that would be limited by the switch resistance alone.

Fig3.1: Inductor current waveformTon Toff

The key advantage is when the inductor is used to drop voltage, it stores energy. Also the inductor controls the percent of the ripple and determines whether or not the circuit is operating in the continuous mode.

1 2

Fig3.2: Continuous (1) and Discontinuous (2) mode

Peak current through the inductor determines the inductor’s required saturation current rating, which in turn dictates the approximate size of the inductor.

Fig3.3: Output voltage ripple of Inductor

Saturating the inductor core decreases the converter efficiency, while increasing the temperatures of the inductor, the MOSFET and the diode. The size of the inductor and capacitor can be reduced by the implementation of high switching frequency, multi-phase interleaved topology, and a fast hysteric controller.A smaller inductor value enables a faster transient response; it also results in larger current ripple, which causes higher conduction losses in the switches, inductor, and parasitic resistances. The smaller inductor also requires a larger filter capacitor to decrease the output voltage ripple.

Critical value of inductor

for Buck converter

Critical value of inductor for

Boost converter

Critical inductance is the minimum value of the inductor for a given K, f and R before the

converter enters the discontinuous conduction mode (dcm) of operation.

Capacitor Selection

The primary criterion for selecting the output filter capacitor is its capacitance and equivalent series resistance, ESR. Since the capacitor’s ESR affects efficiency, low-ESR capacitors will be used for best performance.

For reducing ESR is also possible to connect few capacitors in parallel. The output filter capacitors are chosen to meet an output voltage ripple specifications, as well as its ability to handle the required ripple current stress.

For Buck converter the peak-to-peak ripple voltage is

=

Fig3.4: Ripple voltage in buck capacitor

For Boost converter the peak-to-peak ripple voltage is

Fig3.5: Ripple voltage in boost capacitor

3.2 Design of a Buck converter

A buck regulator has an input voltage of Vs=12V. The required average output voltage is Va

=5V at R = 500 ohm and the peak-to-peak output ripple voltage is 20mV. The switching frequency is 25 kHz. If the peak-to-peak ripple current of inductor is limited to 0.8 A.

Determine:

a) the duty cycle kb) the filter inductance Lc) the filter capacitor Cd) the critical values of L and C.

Solution:

Given,

Vs=12V, f=25 kHz, Va= 5V

a) We know, Va=kVs

or, k=

or, k= =0.4167

or, k=41.67%

So, Duty cycle, k=41.67%

b) The equation of peak-to-peak ripple current is-

or, f LVs=

or, L =

or, L =

or, L =145.83

So, the filter inductance, L = 145.83

C ) The peak-to-peak ripple voltage of the capacitor is-

or, C =

or, C =

or, C = 200

So, the filter capacitor, C=200

d) The critical value of the inductor,

Lc=

or, Lc=

or, Lc = 5.83 mH

Again, The critical value of capacitor,

Cc=

or, Cc=

or, Cc =0.4 .

3.3 Design of a Boost converter

A boost regulator has an input voltage of Vs=5 V. The average output voltage Va=15V and the average load current Ia=0.5 A. The switching frequency is 25 kHz. If L=150 H and

C=220 F,

Determine:

a) the duty cycle k

b) the ripple current of inductor I

c) the peak current of inductor I2

d) the ripple voltage of filter Vc and

e) the critical values of L and C.

Solution:

Given,

Vs=5V, Va=15V, f= 25 kHz, L=150 H, C=220 F

a) We know, the average output voltage,

Va=

or, 1-k=

or, k=1-

or, k= 1-

or, k= 0.6667

or, k= 66.67%

So, Duty cycle k= 66.67%

b) The peak-to-peak ripple current ,

or,

or, 0.89 A

c) We know, The average input current , Is=

or, Is =

or, Is= 1.5 A

And the peak inductor current, I2= Is+ = 1.5+

or, I2= 1.945 A

d) The ripple voltage of filter capacitor,

or,

or, =60.61mV

e) Resistance , R=

or, R=

or, R= 30 ohm

The Critical value of inductor,

Lc=

or, Lc =

or, Lc = 133

The critical value of capacitor, Cc =

Or, Cc =

Or, Cc = 0.44

Chapter 4

Simulation results of DC-DC converters

4.1 Introduction to PSpice

SPICE, the acronym for a Simulation Program with Integrated Circuit Emphasis, was developed at the University of California Berkeley. Pspice is a commercial version, developed by Microsim Corporation. In 1997 Pspice was bought by Orcad, Inc., then in 1998 Cadence bought Orcad. There are two schematic editors available: Capture and Schematic.

The Capture is inherited from Orcad, whilst the Schematic is inherited from Microsim. Microsim’s Schematic Editor is still available now and for the next few years until the Pspice’s users become more familiar with Orcad Capture.

4.2 General procedure to use Pspice Orcad Capture

Circuit simulation in Pspice is a four-step process:

1. Open and draw a circuit file under Orcad Capture2. Simulate3. Plot results using probe4. Analyze the results

A general procedure to use Pspice can be given as follows:1. Open the Orcad Capture

Choose the menu option Start>Programs>Orcad Family Release>Capture CIS

In the Create New Project dialog box, tick Create a Blank Project. Click OK.

2. Create a new Project or open an existing Project Choose the menu option File: New: Project

Give your project a name in the dialog box. Select Analog or mixed A/D Wizard Click OK

Or Choose the menu option File: Open: Project Use the browse button in the dialog to locate the folder containing your Pspice files. Click OK

3. Load Libraries of Parts Choose the menu option Place: Part: Add library

We recommend adding all of the available part libraries. Click OK

4. Choose the Parts for schematic Choose the menu option Place: Part In the Place Part dialog box, choose the specific part by selecting Libraries and Part

list. Click OK.

Locate the part on drawing with mouse, then right click on the mouse and select End Mode.

To rotate a part, select part and type r. To flip a part vertically, select part and type v. To flip a part horizontally, select part and type h.

5. Specify the attributes of the part Double click on the value of the part In the Display Properties dialog box, change the value.

Or Double click on the part. In the Orcad Capture Property Editor, change the attribute values.

The Orcad Capture Property Editor is a spread sheet type, like Excel. We can add a new column, if needed.

A different part requires a different attribute values. Some parts (such as Vdc, R, L, and C) require only one attribute, usually the value of the part, that we must specify; and the other parts (such as VSIN, VPULSE and VPWL) require a few attribute values.

The process of locating a part, placing it on the layout grid and setting the attribute values is repeated for each part of the circuit.

6. Wire the schematic Choose the menu option Place: Wire Locate wire on drawing with mouse, then right click on the mouse and select End

Mode.

7. Grounding the circuitThe Ground is always required for any circuits that we want to simulate using Pspice.

Choose the menu option Place: Ground In the Place Ground dialog box, choose Add Libraries. In the Browse File dialog box

select Source, and then click Open. In the Place Ground dialog box again, select Source in the Libraries and select 0.

8. Place Voltage and/or current probes (optional) Choose the menu option Pspice: Marker: Voltage level if needed

Choose the menu option Pspice: Marker: Voltage differential if needed Choose the menu option Pspice: Marker: Current into pin if needed

9. Setup the simulation Choose the menu option Pspice: New Simulation ProfileGive simulation profile a name in the dialog box.

In the simulation setting dialog box, select Analysis TypeThe available analysis types are Time domain (transient), DC sweep, ACSweep/Noise and Bias point.

Set Run to Time (TSTOP)For a typical Time domain analysis, one to ten cycles of the input source is often required.(e.g. for 50 Hz source, Run to time (TSTOP) of 60 ms (three cycles) is enough)

10. Run simulation and display the results. Choose the menu option Pspice: Run The probe window will be prompted automatically. The results for the marked

current/voltage probes will be displayed. In the Probe Window choose the menu option Trace: Add trace if needed. In the Probe Window choose the menu option Trace: Eval goal function if needed In the Probe Window choose the menu option Plot: Add Plot to window if needed In the Probe Window choose the menu option Plot: Axis setting if needed

Important Parts selection

Name Part’s name figureInductor L/design cache

MOSFET IRF 540/ design cache

Square wave pulse generator Vpulse/ design cache

Capacitor C_elect/ design cache

Diode D1N4007/ design cache

4.3 Simulation results of Buck converter

Fig 4.1: PSpice circuit for the simulation of Buck converter

5 Volt gate pulse applied to the MOSFET IRF540 Circuit operating at continuous conduction mode. L1 >> Lc

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 18 s 0.45 50mH 47 f 12V 10 KΩ

Input Parameters table

Fig 4.2: output voltage of Buck converter

Simulation has been taken up to 1 second. Output voltage becomes steady at almost 600 ms

Fig 4.3(a): Output voltage when L= 35 mH

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 18 s 0.45 35 mH 47 f 12V 10 KΩ

Inductor value changed from 50 mH to 35 mH Output voltage taking slightly more time to become steady Slightly less stepped down output voltage

Fig 4.3(b): Output voltage when L= 20 mH

Inductor value changed from 50 mH to 20 mH Output voltage taking more time to become steady

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 18 s 0.45 20 mH 47 f 12V 10 KΩ

Fig 4.3(c): output voltage when L= 60 mH

Inductor value changed from 50 mH to 60 mH Output voltage becomes steady at almost 550 ms Slightly much stepped-down

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 18 s 0.45 60 mH 47 f 12V 10 KΩ

Fig 4.3(d): output voltage when L=75 mH

Inductor value changed from 50 mH to 75 mH Output voltage becomes steady little much earlier Little more stepped-down than previous one

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 18 s 0.45 75 mH 47 f 12V 10 KΩ

Fig 4.4(a): output voltage when C= 20 f

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 18 s 0.45 50 mH 20 f 12V 10 KΩ

Capacitor value has been changed from 47 f to 20 f

Transient period is much shorter due to lower capacitance

Steady state occurs at almost 250 ms

Fig 4.4(b): output voltage when C= 65 f

Capacitor value has been changed from 47 f to 65 f

Higher capacitance value significantly increases transient period

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 18 s 0.45 50 mH 65 f 12V 10 KΩ

Fig 4.5(a): output voltage when f= 40 KHz

Frequency has increased from 25 KHz to 40 KHz Large ripple voltage at the output

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

40 KHz 25 s 12 s 0.48 50 mH 47 f 12V 10 KΩ

Fig 4.4(b): output voltage when f= 100 KHz

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

100 KHz 10 s 5 s 0.5 50 mH 47 f 12V 10 KΩ

Frequency increased to 100 KHz Significantly low stepped down Still ripples are in output voltage

Fig 4.5(c): output voltage when f= 15 KHz

Frequency decreased to 15 KHz Very low ripple voltage with higher stepped down

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

15KHz 66.66 s 30 s 0.45 50 mH 47 f 12V 10 KΩ

4.4 Simulation results of Boost converter

Fig 4.6: PSpice circuit for the simulation of Boost converter

5 Volt gate pulse applied to the MOSFET IRF540 Circuit operating at continuous conduction mode. L1 >> Lc

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 25 s 0.625 20mH 47 f 12V 10 KΩ

Input Parameters Table

Fig 4.7: Output voltage of Boost converter

Simulation has taken up to 1.5 second Output voltage becomes steady at 850 ms and at 70 vol

Fig 4.8(a): Output voltage when L= 10 mH

Inductor value has changed from 20 mH to 10 mH Shorter transient period, small amount of ripple at output voltage Become steady at about 75/74 volt

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 25 s 0.625 10mH 47 f 12V 10 KΩ

Fig 4.8(b): output voltage when L= 1 mH

Inductor value has change from 20 mH to 1 mH Significant change in output voltage, large transient peak voltage has dropped down. Ripple voltage is slightly higher

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 25 s 0.625 10mH 47 f 12V 10 KΩ

Fig 4.8(c): output voltage when L= 500

Inductor value has changed to 500

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 25 s 0.625 1mH 47 f 12V 10 KΩ

Stepping up around 55 volt

Fig 4.8(d): output voltage when L= 35 mH

Inductor value increased to 35 mH No visible change in output voltage compared to 20 mH inductance except increase in

transient peak

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 25 s 0.625 35mH 47 f 12V 10 KΩ

Fig 4.5(e): Output voltage when L= 60 mH

Inductor value increased to 60 mH

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 25 s 0.625 60mH 47 f 12V 10 KΩ

Very high transient peak of almost 350 volt, becomes steady nearly at 78 volt

Fig 4.9: output voltage with changed C= 100

Capacitor value has increased to 100

Transient period has increased significantly

Frequency

Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

25 KHz 40 s 25 s 0.625 20mH 100 f 12V 10 KΩ

Fig 4.10(a): Output voltage when f= 40 KHz

Frequency has been change from 25 KHz to 40 KHz Increased frequency just stepped up the voltage to 120 volt

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

40 KHz 25 s 12 s 0.48 20 mH 47 f 12V 10 KΩ

Fig 4.10(b): Output voltage when f= 60 KHz

Frequency changed to 60 KHz Increase in frequency causing drop in output voltage

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

60 KHz 16.66 s 7 s 0.42 20 mH 47 f 12V 10 KΩ

Fig 4.10(d): Output voltage when f= 10 KHz

Frequency decreased to 10 KHz

Frequency Period On periodTon

Duty cycle

Inductance Capacitance Input voltage

Load resistance

10 KHz 100 s 45 s 0.45 20 mH 47 f 12V 10 KΩ

Very low frequency also degrade the output voltage as we can see steady state voltage dropped to almost 25 volt only

Chapter 5

Conclusion

This thesis paper concerns with the design and simulation of ideal DC-DC converters. This is a theoretical and simulation based project because the converters are ideal in this case. It’s really tough to obtain desired output from a practical ideal circuit. But the content and simulation results we included in this paper could be really helpful to get an overall idea on buck and boost converters.

From the simulation results it’s found that in case of these buck and boost converter, the desired output voltage can be obtained by selecting proper value of inductor, capacitor and switching frequency.

All these individual theories were difficult for us to grasp initially and putting them together in the simulator was extremely confusing. But we tried our best to make an exceptional project paper with rich in its content. At each stage, targets were set to acquire the necessary skills to meet the criteria of the project and design the circuits for implementation into the software simulation.

This project gives the opportunity to learn new skills and gain valuable experience in circuit designing and problem solving skills. This project has greatly enriched our knowledge and understanding through the learning process which may help us in our future advancement.

References

1. Muhammad H. Rashid ,Power Electronics Circuits, Devices and Application, Third edition

2. Robert W. Erickson and Dragon Maksimonic, Fundamentals of Power Electronics, Second Edition, Springer International Edition

3. "Generalized Analysis of Soft-Switching DC-DC Converters", by Jaber Abu-Qahouq and Issa Batarseh, ISCAS 2000 – IEEE International Symposium on Circuits and Systems, May 28-31, 2000, Geneva, Switzerland

4. R. Tymerski and V. Vorperian, “Generation, Classification and Analysis of Switched-mode DC-to-DC converters by the use of Converter cells,” in Proc. INTELEC’86, pp. 181–195, Oct. 1986.

5. R. D. Middlebrook, Power electronics: topologies, modeling, and measurement, Proc. IEEE Int. Symp. Circuits Syst., April 1981.

6. Dr. Zainal Salam, Power Electronics and Drives (Version 2)

7. Wikipedia, the Free Encyclopedia, ‘Buck converter [online], Available from http://en.wikipedia.org/wiki/Buck_converter

8. Wikipedia, the Free Encyclopedia, ‘Boost converter [online], Available from http://en.wikipedia.org/wiki/Boost_converter