2. Content
• Introduction
• Basics of DC-DC Converter
• Types of DC-DC Converter
Buck Converter or Step-Down Chopper
Boost Converter or Step-Up Chopper
• Design and Simulation of Buck Converter using MATLAB / Simulink
• Design and Simulation of Boost Converter using MATLAB / Simulink
• Design and Simulation of PV System with Boost Converter
• Design of PV System with MPPT and Boost Converter using MATLAB / Simulink
Source: L&T EduTech Team
3. Introduction
• A DC-DC Converter is a power converter that converts a source of direct
current (DC) from one voltage level to another, by storing the input energy
temporarily and then releasing that energy to the output at a different
voltage.
• The store of electric energy may be done in either magnetic field storage
components (inductors, transformers) or electric field storage components
(capacitors).
• DC-DC converter is needed to convert and stabilize voltage. A device that
stabilize the voltage using DC-DC converter is referred to as a voltage
regulator.
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4. Key Applications of DC-DC Converter
• Renewable Energy Integration
• Electric Vehicles
• Smart Lighting
• Spacecraft Power Systems
• DC Motor Drives
• Battery Systems
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5. Duty Cycle of a DC-DC Converter
• The duty cycle of DC-DC converter is the ratio of the on-time to the total
switching period of the converter.
• Important parameter in the design and operation of DC-DC converters.
• The duty cycle determines the average output voltage of the converter and is
used to control the power transfer from the input to the output.
• Duty Cycle = Ton / (Ton+Toff), where Ton is the on-time and Toff is the off-
time of the switching period.
• Suppose the switching frequency is 2 MHz, which means switching period
T=1/2 MHz=500 ns, If the duty is 0.5 or 50%, then the on-time is 250 ns and
off time is 250 ns.
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7. Buck Converter
• A buck converter or step down converter is a DC-to-DC converter which
decreases voltage, while increasing current, from its input (supply) to its
output (load).
• It is also called as Step-down DC to DC Converter or Step-down Chopper or
Buck Regulator.
• The DC input for the buck converter can be derived from rectified AC or
from any DC supply or battery unit.
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9. Design of Components in Buck Converter
• Given:
Vin=48 V, Vout=15 V (expected), R=8 Ohm, fs=40 KHz.
Step 1: Determine the duty ratio
D=Vout / Vin = 15 V / 48 V = 0.3125 = 31.25 %
Step 2: Determine Inductance Value (L)
Lmin=(1-D)R/2fs = (1-0.3125) 8 / 2 * 40k = 68. 75 micro Henry.
Assume 25 % safety margin for L (for inductor current to be
continuous)
Lactual = 1.25 * Lmin = 1.25 *68.75 = 85.93 micro Henry
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10. Design of Components in Buck Converter
Step 3: Determine Capacitance Value (C)
C=(1-D) / 8L (Ripple Factor) f2
Assume Ripple factor to be less than 5%
C=(1-0.3125) / (8*85.93(0.05)(40*103)2=12.5 micro Farad.
• Choose MOSFET rating with operating voltage atleast two times the output
voltage and operating current atleast three times the output current
• As per EMI standards, switching frequency range is 20 kHz to 2 MHz for
conveters / inverters
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15. Boost Converter
• A boost converter or step-up converter is a DC- to – DC converter that
increases voltage, while decreasing current, from its input (supply) to its
output (load).
• It is also called as Step-Up DC to DC Converter or Step-Up Chopper or
Booster.
• The DC input for the boost converter can be derived from rectified AC or
from any DC supply or battery unit.
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17. Components in MATLAB Simscape – Boost Converter
• DC Voltage Source
• MOSFET (including with snubber circuit)
• Pulse Generator (to trigger Gate of MOSFET)
• Diode (included with Snubber Circuit)
• Series RLC Branch (converted to Inductance)
• Series RLC Branch (converted to Capacitance)
• Series RLC Branch (converted to Resistance)
• Voltage Measurement (to measure output voltage)
• Scope (to view the output voltage graphically)
• Continuous Powergui
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20. PV Array Configuration and Specifications
• Model Make : Trina Solar TSM 350DEG 14 (II)
• Max. Output Power (Pmax) = 349.965 W
• No. of cells per module (Ncell) = 72
• Open Circuit Voltage (Voc) = 46.9 V
• Short Circuit Current (Isc) = 9.6 A
• Max. Peak Voltage (Vmp) = 38.5 V
• Max. Peak Current (Imp) = 9.09 A
• Temperature Coefficient of Voc = -0.3014 % / deg. C
• Temperature Coefficient of Isc = 0.054604 % / deg. C
• No. of Parallel Strings = 1
• Series Connected modules per string = 2
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23. PV Array Configuration and Specifications
• Model Make : Trina Solar TSM 350DEG 14 (II)
• Max. Output Power (Pmax) = 349.965 W
• No. of cells per module (Ncell) = 72
• Open Circuit Voltage (Voc) = 46.9 V
• Short Circuit Current (Isc) = 9.6 A
• Max. Peak Voltage (Vmp) = 38.5 V
• Max. Peak Current (Imp) = 9.09 A
• Temperature Coefficient of Voc = -0.3014 % / deg. C
• Temperature Coefficient of Isc = 0.054604 % / deg. C
• No. of Parallel Strings = 2
• Series Connected modules per string = 2
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24. PV Array with MPPT Boost Converter Design
Parameters
• Duty Ratio will be determined by MPPT
• Switching frequency = 5 kHz
• Sample Time = 5e-6 sec
• Load Resistance = 20 Ohm
• Lactual = 2 mH
• C=100 MicroFarad
• Capacitance connected across PV array = 100 micro Farad (to supress input
voltage ripple and filter ripple current).
• Constant (delta) for MPPT =125e-6
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25. MATLAB Script for P&O Algorithm
• The function gets PV array voltage, PV array current and a constant value
delta as input arguments and gives duty cycle as output or return value.
• Initialize the minimum, maximum and initial value of duty cycle.
• Initialize the interval values of Vpv, Ppv, and duty cycle for the initial run.
• Calculate the PV power and change in Power and Change in Voltage.
• Check if change in power and change in voltage is less than zero and vary
the duty cycle by incrementing / decrementing from the original value.
• Check whether the calculated duty cycle is within the minimum / maximum
value already initialized else not to min. or max. value whichever violates.
• Update the values of Vpv, Ppv and duty cycle with the newly calculated
values for the next run.
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26. Components in MATLAB Simscape – PV with MPPT and
Boost Converter
• PV Array
• Constant (for Irradiance and Temperature)
• MATLAB Function (for P&O Algorithm)
• PWM Generator
• Goto and from Blocks
• MOSFET (including with snubber circuit)
• Diode (included with Snubber Circuit)
• Series RLC Branch (converted to Inductance)
• Series RLC Branch (converted to Capacitance)
• Series RLC Branch (converted to Resistance)
• Voltage Measurement (to measure output voltage and input voltage)
• Current Measurement (to measure output current and input current)
• Scope (to view the output voltage graphically)
• Continuous Powergui
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27. MATLAB Built-in Model for PV System with MPPT
and Boost Converter
• Type the following in the command prompt in MATLAB
open example (‘simscapeelectrical/SolarPVMPPTBoostExample’)
• To open a script that design the Solar PV system with MPPT using boost
converter, at the MATLAB command line, enter:edit
‘SolarPVMPPTBoostData’
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