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DC TO DC CONVERSION
(CHOPPER)
ET502
POWER ELECTRONICS
PUAN HJH HANIFAH BINTI JAMBARI
Contents:
•
•
•
•
•
Objectives
Types of power electronics conversion
Revise of RECTIFIER
Chopper Definition
Type of Chopper
Learning Objectives
After completing this class, the student
should be able to:
1.
2.
3.
4.
Explain what the term chopper means
Lists on 4 types of DC – DC converter
Describe the basic operation of buck chopper
Describe the basic operation of boost chopper
Tasks of Power Electronics
•
•
•
•
AC –to- DC conversion - RECTIFIER
DC-to DC conversion - CHOPPER
DC-to-AC conversion - INVERTER
AC-to-AC conversion - CONTROLLER
RECTIFIER
 RECTIFICATION - referring to conversion of ac voltage to dc voltage
Vin
Vout
 TYPE OF RECTIFIER
1. Half bridge
2. Full Bridge
-uncontrolled rectifier, semi-controlled rectifier and controlled rectifier
CHOPPER
• DEFINITION: Converting the unregulated DC input (from
rectifier) to a controlled DC output with a desired voltage
level (regulated DC output).
• In other words Chopper is used to obtain a variable DC
voltage from a constant-voltage DC source using Power
electronics semiconductor devices(SCR, Thyristor,
GTO,IGBT, Mosfet, etc).
• Basic block diagram•
Vac
RECTIFIER
Vdc
CHOPPER
Vdc
M
TYPES OF SWITCH MODE DC-DC
CONVERTERS
There are basically four types of switch mode power
converter. These are,
1) Buck Converter (Step Down Converter )
2) Boost Converter ( Step up Converter )
3) Buck Boost Converter ( step up/step down Converter )
and
4) Cuk Converter
The first three converters operate with the help of inductive
power transfer principle, whereas, the Cuk converter
operates with capacitive power transfer principle.
To page 10
APPLICATIONS:
–Switched-mode power supply
(SMPS)*, DC motor control
speed, battery chargers, monorail
system ,marine, industrial,
transportation(hybrid car), mobile,
and other applications.
* Switch mode power supplies are high frequency dc to dc
converters capable of stepping up and down the dc according need
but are limited to low power applications in power supplies of
computers, TVs, VCRs, and other electronic appliances.
ADVANTAGES OF DC –DC CONVERTER
1.
DC is only a real number, thus simplifying the analysis.
2.
DC system has the ability to transform voltage into
various levels, and efficiently
3.
Using DC can be save cost and energy as an example in
hybrid car
4.
In DC system, the power is just the real component.
1. Buck (step-down) converter
-The circuit is used
to obtain low output
Voltage compared to
the input voltage
-O/put can be
controlled
0 < Vo < Vi
Buck converter:
Circuit operation when switch is turned on (closed)
• Diode is reversed biased.
Switch conducts inductor
current
• This results in positive
inductor voltage, i.e:
Vo = V
Vo = α V
α= duty ratio 0< α < 1
• It causes linear increase in
the inductor current
To Page 7
Buck converter:
Circuit operation when switch is turned off (Opened)
• Because of inductive
energy storage, iL
continues to flow.
• Diode is forward
biased
• Current now flows
through the diode and
to the load for certain
time until the energy
store is zero.Therefore;
Vo = VD = 0 V
• If t = T, switch is closed again, this cycle is
continuous until the power supply is not
connected to the circuit
• The load current was flow continuous with
positive value
• The output voltage consider as a chopper
voltage with discontinuous mode
• This buck converter only can produced positive
output voltage and current.
• ON and OFF switches can be controlled using
(constant switching)
• Output Voltage can be calculated as
below:
Vo = αV
= ton x V
T
Whereas, ton = time for chopper on
T = time for one cycle( T = ton + toff)
α = duty ratio ( o < α < 1)
α
Question
1. If the V is 10 V and the duty ratio is 0.5. Calculate
the output voltage (Vo)
2. Given value of ton and toff are 0.8s and 0.2s
respectively for buck chopper. Find the values of:
a.
time for on cycle (T)
b.
duty cycle,
α
c.
output voltage if the input voltage is 20V
3. Given T =1.5 s, Vo= 30V
a.
If Vi = 50, calculate duty cycle, α
b.
If α = 0.2, calculate input voltage (Vi) and
ton
Conclusion
• Output voltage can be varied by changing the value of duty cycle .
• Buck converter is used to produce lower output voltage compared to
input voltage
http://www.hanifah671.blogspot.com
http://encon.fke.utm.my/notes/MSc-Chopper.pdf
References
• Power Electronics for Technology, Ashfaq Ahmed,
Prentice Hall
• Power Electronics, Mr C. Aravind Vaithilingam,
Salem India
• Power Electronics Circuit, Devices and
Application, Muhammad H. Rashid, Pearson
Prentice Hall.
REVIEW
• Q1: Definition of Chopper
• Q2: Chopper types
• Q3: Buck Converter