EET223-W21-EXP 6 - DC to DC converters - Instructions PDF

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Lab 6...

Description

School Of Engineering Technology and Applied Science (SETAS) Advanced Manufacturing and Automation Technology (AMAT) SECTION: 003 EET223– Lab instruction

Experiment No. 6

NAME : Deanne Aira P. Pimentel

DC to DC Converters

STUDENT ID: 301093498

Objective

Design, construct, and investigate the operation of DC to DC converters circuit such as Buck converter, boost converter, and buck-boost converter.

Introduction DC-DC converters are power electronic circuits that convert a dc voltage to a different dc voltage level, often providing a regulated output. Examples of such applications are subway cars, trolley buses, battery operated vehicles etc. The circuits described in this lab are classified as switched-mode dc-dc converters. We can control and vary a constant DC voltage with the help of a chopper. We mainly investigate two topology for DC to DC converters: 1) Buck converter: The step-down dc–dc converter, commonly known as a buck converter, shown Figure 1. The state of the converter in which the inductor current is never zero for any period of time is called the continuous conduction mode(CCM). 2) Boost converter: Step up chopper or boost converter is used to increase the input voltage level of its output side. Figure 1 depicts a step-up or a boost converter. It is comprised of dc input voltage source VS , boost inductor L, controlled switch S, diode D, filter capacitor C, and load resistance R.

Figure 1 – left: Buck Converter, right: Boost Converter 3) Buck-Boost converter: With the help of Buck-Boost converter we can increase or decrease the input voltage level at its output side as per our requirement. The circuit diagram of this converter is shown below. Sources : •

•

Figure 2 – Buck Boost Converter

EET223-Experiment # 6 – INSTRUCTION

https://www.electrica l4u.com/chopper-dcto-dc-converter/ Power Electronics , Daniel W. Hart , McGraw Hill Publishing Copyright © 2011 , ISBN 978-007-338067-4

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Procedure:

Part 1: Buck (Step Down) Converter 1.1 – Open Multisim 14.2 Simulation software. 1.2 – Click on Place and then Component (Or short cut: Ctrl+W) 1.3 – According to the table below add the indicated components to the main area. Select a component Transistor (Switch)

Data Base Master Database

Pulse Generator Resistors

Group

Family

Component

Symbol

Label and value

Power

SWITCHES

TRANSISTOR

-

Master Database

Sources

DIGITAL_SOURCES

DIGITAL_CLOCK

Master Database Master Database Master Database

Basic

RESISTOR

20 Ω

f= 20 kHz D= 40% Delay = 0 s R1 = 20 Ω

Basic

INDUCTOR

400μ

L1= 400 μH

Basic

CAP_ELECTROLIT

100μ

C1=100μF

Master Database Master Database

Diodes

Diode

1N4004G

D1

Sources

POWER_SOURCES

DC_POWER

V_S1=50 V

Ground

Master Database

Sources

Power Sources

Ground

-

Oscilloscope

Current Clamp

Pick the Multisim Tektronix oscilloscope from the Instrument menu. Find the current clamp in instrument bar located on the right of working area.

XCS1 Set to 1 mV/mA

Voltmeter

Use a voltage probe by Going to Place>Probe> Voltage

PR _OUT

Inductor Capacitor Diode DC Supply

1.4 – To change the value or label of a component, double click on the component and change the name (RefDes) from the Label tab and change the value from Value tab. 1.5 – Make the required connection to build Circuit 1:

EET223-Experiment # 6 – INSTRUCTION

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IL

S1

VS

D1

+

50 V

1N4004G

L1 400 μH C1

Output Voltage Probe

+

R1

+

100 μF

20 Ω

VO -

Pulse Generator 20 kHz, D=40%

Circuit 1 – Buck DC to DC converter 1.6 – Run the simulation. Click on the oscilloscope and make sure to set the channel A scale to 10V/div, channel B scale to 1V/div, and horizontal scale to 20 μs/div Capture the image of Oscilloscope and insert it below. Center both waves to the middle. Capture the oscilloscope image and insert it below.

Image 1: Oscilloscope Image Buck Converter

1.7 – Measure value of following parameters indicated in Table 1 and record them.

Parameters

Measured Value

Calculated Value

DC Output Voltage [V]

19.5 V

20 V

Ripple Output Voltage [mV]

91.0 mV

93.75 mV

Maximum Inductor Current [A]

1.74 A

1.75 A

Minimum Inductor Current [A]

209 A

250 mA

Table 1 – Voltage value of output and inductor current for Buck converter

EET223-Experiment # 6 – INSTRUCTION

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1.8 – Find the calculated values of the above mentioned parameters using formula below and write them in Table 1. • •

•

Output Voltage ( D is Duty cycle of ON/OFF switch) ฀฀฀ ฀ = ฀฀฀฀฀฀ Output Ripple Voltage ฀฀ − ฀฀ ฀฀ ∆฀฀฀ ฀ = ฀฀฀฀฀฀฀฀฀ ฀ ฀฀ Maximum and minimum inductor current : ฀฀ (฀฀ − ฀฀) ) ฀฀฀฀฀฀฀฀ = ฀฀฀฀ ( − ฀฀฀฀฀฀ ฀฀ ฀฀ (฀฀ − ฀฀) ) ฀฀฀฀฀฀฀฀ = ฀฀฀฀ ( + ฀฀฀฀฀฀ ฀฀

1.9 – Stop the simulation and change the simulation type to Transient.

Figure 3 – Change simulation type to transient 1.10 – Select Transient and change End time (TSTOP) to 0.02 seconds.

Figure 4 – Selecting transient simulation duration 1.11 – Click on Output tab and from right column select voltage probe V(PR1) and add it to analog graph. Press Save.

EET223-Experiment # 6 – INSTRUCTION

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Figure 5 – Adding the transient parameter 1.12 – Run the simulation. A graph will be pop up. Insert the transient output voltage graph below:

Image 2: transient voltage of Buck Converter with D=40%

1.13 – Change the duty cycle of the switch to 70% and run the transient simulation again.

Image 3: transient voltage of Buck Converter with D=70%

1.14 – Stop the simulation. EET223-Experiment # 6 – INSTRUCTION

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Part 2: Boost (Step-Up) Converter: 2.1 – Create a new page by going to Place > Multi-Page... 2.2 –Change the simulation type to Interactive. Following same steps as Part 1 build CIRCUIT 2 below:

L2 120 μH IL D2 1N4004G

VS2

+

S2

12 V

C2

100 μF

+

R2

Output Voltage Probe

20 Ω

Pulse Generator 20 KHz , D=60%

Circuit 2 – DC to DC Boost Converter 2.3 – Run the simulation. Click on the oscilloscope and make sure to set the channel A scale to 10V/div, channel B scale to 5V/div, and horizontal scale to 10 μs/div Capture the image of Oscilloscope and insert it below. Center both waves to the middle. Wait until output voltage becomes steady. Capture the oscilloscope image and insert it below.

Image 4: Oscilloscope Image Boost Converter

EET223-Experiment # 6 – INSTRUCTION

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2.4 – Measure value of following parameters indicated in Table 2 and record them.

Parameters

Measured Value

Calculated Value

DC Output Voltage [V]

28.9 V

30 V

Ripple Output Voltage [mV]

432 mV

450 mV

Maximum Inductor Current [A]

5.1 A

5.25 A

Minimum Inductor Current [A]

2.11 A

2.25 A

Table 2 – Voltage value of output and inductor current for Boost Converter 2.5 – Find the calculated values of the above mentioned parameters using formula below and write them in Table 1. •

Output Voltage ( D is Duty cycle of ON/OFF switch) ฀฀ ฀฀฀ ฀ = ฀฀ ฀฀ − ฀฀ ฀฀

•

Output Ripple Voltage ฀฀ ∆฀฀฀ ฀ = ฀฀ ฀฀฀฀฀฀ ฀฀

•

Maximum and minimum inductor current : ฀฀ ฀฀ − ) ฀฀฀฀฀฀฀฀ = ฀฀฀฀ ( ฀฀ (฀฀ − ฀฀) ฀ ฀ ฀฀฀฀฀฀ ฀฀ ฀฀ + ) ฀฀฀฀฀฀฀฀ = ฀฀฀฀ ( (฀฀ − ฀฀)฀฀ ฀ ฀ ฀฀฀฀฀฀

2.6 – Stop the simulation and change the simulation type to Transient. Select Transient and change End time (TSTOP) to 2 seconds. 2.7 – Click on Output tab and from right column select Inductor current I(L2) and add it to analog graph. Press Save. 2.8 – Run the simulation. A graph will be pop up. Insert the transient output voltage graph below:

Image 5: transient graph for Inductor Current of Boost Converter

EET223-Experiment # 6 – INSTRUCTION

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2.9 – Stop the simulation. Save your file as:

EET223 –Sec (choose your section)–Lab 6 -(Your name ) 2.10 – Well Done! Answer the following questions and submit this document along with multisim file on ecentennial.

Conclusion: At the end of the lab, I learned about the different types of choppers or DC-DC converters. As its name implies, a DC-DC converter converts one DC voltage to another. It can be configured as a buck, boost, or buck-boost DC-DC converter. A Buck Converter gives a lower voltage A Buck Converter outputs a lower voltage than the original voltage, while a Boost Converter supplies a higher voltage than the original voltage, while a Boost Converter supplies a higher voltage. While a buck– boost converter is a type of DC-to-DC converter that has an output voltage that is either greater than or less than the input voltage.

Questions: Q1. In Circuit 1 when duty cycle changes from 40% to 70% what would happen to following parameters? •

Output Voltage : Output Voltage at 40% Duty Cycle = 20 V Output Voltage at 70% Duty Cycle = 35 V Thus, when duty cycle changes from 40% to 70%, output voltage increases.

•

Ripple output voltage: Ripple Output Voltage at 40% Duty Cycle = 93.75 mV Ripple Output Voltage at 70% Duty Cycle = 70.31 mV Thus, when duty cycle changes from 40% to 70%, ripple output voltage decreases.

•

Maximum Inductor Current : Imax at 40% Duty Cycle = 1.75 A Imax at 70% Duty Cycle = 2.41 A Thus, when duty cycle changes from 40% to 70%, maximum inductor current increases.

•

Minimum Inductor Current : Imin at 40% Duty Cycle = 250 mA Imin at 70% Duty Cycle = 1.09 A Thus, when duty cycle changes from 40% to 70%, minimum inductor current increases.

Q2. In Circuit 1 when frequency of switch decrease from 20 KHz to 1 KHz, what would happen to following parameters? •

Output Voltage : Output Voltage at 20 kHz = 20 V Output Voltage at 1kHz = 20 V Thus, when frequency from 20kHz to 1kHz, output voltage stays the same.

•

Ripple output voltage: Ripple Output Voltage at 20 kHz = 93.75 mV Ripple Output Voltage at 1kHz = 37.5 V Thus, when frequency changes from 20kHz to 1kHz, ripple output voltage increases.

•

Maximum Inductor Current : Imax at 20 kHz = 1.75 A Imax at 1kHz = 16 A Thus, when frequency changes from 20kHz to 1kHz, maximum inductor current increases.

•

Minimum Inductor Current : Imin at 20 kHz = 250 mA Imin at 1kHz = -14 A Thus, when frequency changes from 20kHz to 1kHz, minimum inductor current decreases.

EET223-Experiment # 6 – INSTRUCTION

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Q3. A boost converter is required to have an output voltage of 8 V and supply a load of 10Ω. The input voltage is 3 V. The switching frequency is 100 KHz. a) What is the switching duty cycle? b) Determine a value for inductor of the circuit such that the current in inductor will not change more than 1A. c) Determine a value of a capacitor such that output voltage ripple is no more 2% of output voltage. ( ∆฀฀0 ฀฀0

= 0.02)

a) Vo = (1/1-D)(Vs); D = (Vo - Vs)/Vo = (8V - 3V)/8V = 0.625 = 62.5 %, ans. b) Imin = Vs (1-(1-D)^2(R) + D/2Lf) 1A = 3V (1/(1-0.625)^2(10ohs) + 0.625/2(L)(100kHz) L = 8.272 uH, ans. c) ΔVo = (D/RCf) Vo C = DVo/ΔVoRf 1/C = 0.02 (10ohms)(100kHz)/0.065 C = 3.25 uF, ans.

Q4. In Circuit 3, a buck-boost converter circuit is shown. a) Determine the output voltage. b) Determine the value of inductance (L) so the inductor current stay continuous (IL(min) =0 and find L) ฀฀ ฀฀ ฀฀฀฀฀฀฀฀ = ฀฀฀฀ ( − ) ฀฀ (฀฀ − ฀฀) ฀ ฀ ฀฀฀฀฀฀ D

S1 VS +

24 V

L

C 80 μF

+

R 5Ω

Pulse Generator 100KHz D=40%

Circuit 3 – DC to DC Buck-Boost Converter

Vo = -Vs (D/1-D) Vo = -24V (0.4/1-0.4) = -16 V, ans. 0 A = 24V (1/(1-0.4)^2(5ohms) - 0.4/2(L)(100kHz) L = 3.6 uH, ans.

EET223-Experiment # 6 – INSTRUCTION

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