Project 3
AIM: Design and simulation of Buck converter for Auxiliary load in EV.
- Input voltage is 48V, Output voltage is 12 V
- Load current is 10A
- Calculate Duty ratio and Load(use Resistor as Load)
- Calculate L,C
What is buck converter ?
Buck Converter is a type of chopper circuit that is designed to perform step-down conversion of the applied dc input signal. In the case of buck converters, the fixed dc input signal is changed into another dc signal at the output which is of lower value. This means it is designed to produce a dc signal as its output that possesses a lower magnitude than the applied input.It is sometimes called Step-down DC to DC Converter or Step-down Chopper or Buck Regulator
This buck converter having following controlling uits
1)Switching power supply unit which, can turn ON/OFF switching elements that can be turned ON/OFF at high frequency to convert a dc input voltage Vin into a dc output voltage Vout.
2)Control unit, which is used to control the ON/OFF operation of the switching element. We use MOSFET as switching element where the pulse generator is a control unit for MOSFET.
3)Inductor - It stores the energy during ON period & dissipates during OFF period.
4)Capacitor- It bypass the ripple content in the output voltage
5)Freewheeling diode- It freewheel the current through the resistor from the inductor & circuilate it in circuit during OFF period.
6)Load Resistor- Across it we can measure the output voltage & current through it
CALCULATION:
Given data,
Input Voltage Vin = 48 V
Output Voltage Vout = 12 V
Load current iL = 10 A
Mathematical Formulae:
Output Voltage = Load resistor * Load current
Vout = R * iL
Load Resistor = Output Voltage / Load current
%Duty ratio D = (Vout / Vin) * 100
Minimum Inductance Lmin = [(1-D)*R] / (2*f)
Maximum Inductance L = 1.25 * Lmin
Capacitance C = (1-D) / (8*L*r*f^2)
Ripple factor r = Change in output voltage / rated output voltage
Assumptions:
1)The switching frequency(f) of the buck convertes is taken to be 40 KHz.
2)Ripple factor (r) is assume to be 0.5%
Calculations-
Load resistor R = Vout / iL = 12/10 = 1.2 ohm
Duty ratio(cycle) D = Vout / Vin = 12 / 48 = 0.25
% D = = 0.25*100 = 25%
Minimum Inductance Lmin = [(1-D)*R] / (2*f)
Lmin = [(1.025)*1.2] / (2*40000) = 11.25 micro henry
Maximum Inductance L = 1.25 * Lmin = 14 micro henry
L = 1.25 * Lmin = 14 micro henry.
Capacitance C = (1-D) / (8*L*r*f^2)
C = (1-0.25) / (8*14*10^-6*r*40000^2) = 837 micro farad
SIMULINK MODEL:
In this model we have consider the following blocks
1)DC VOLTAGE SOURCE:
This block is used for the Input providing 48V. The DC Voltage Source block represents a constant voltage source whose output voltage value is independent of the current through the source.here we are taking 48V of input voltage
2)DIODE:
Implements a diode in parallel with a series RC snubber circuit. In on-state, the Diode model has an internal resistance (Ron) and inductance (Lon). For most applications, the internal inductance should be set to zero. The Diode impedance is infinite in off-state mode.
3)Control unit:
We use the pulse generator as Control unit. Control unit parameter input is given through duty cycle.
4)SWITCHING TRANSISTOR:
MOSFET and internal diode in parallel with a series RC snubber circuit. When a gate signal is applied the MOSFET conducts and acts as a resistance (Ron) in both directions. If the gate signal falls to zero when the current is negative, the current is transferred to the antiparallel diode.
5)INDUCTOR:
Use the 'Branch type' parameter to add or remove elements from the branch
6)CAPACITOR:
this block is used for the storage of the electric energy for providing Output voltage when required
7)DUTY RATIO(D):
It is nothing but the ratio of the input voltage source to Output voltage is known as duty ratio its formula is shown below and find out the value.
duty ratio (D) = Vo/Vs
= 12/48
= 1/4
=0.25
8)FROM block:
Receive signals from the Goto block with the specified tag. If the tag is defined as 'scoped' in the Goto block, then a Goto Tag Visibility block must be used to define the visibility of the tag. After 'Update Diagram', the block icon displays the selected tag name (local tags are enclosed in brackets, [], and scoped tag names are enclosed in braces, {}).
9)GOTO block:
Send signals to From blocks that have the specified tag. If tag visibility is 'scoped', then a Goto Tag Visibility block must be used to define the visibility of the tag. The block icon displays the selected tag name (local tags are enclosed in brackets, [], and scoped tag names are enclosed in braces
10)DISPLAY:
This block uses the display of the Output value of Voltage, Current & input volltage
11)SCOPE:
The Simulink Scope block and DSP System Toolbox Time Scope block display time domain signals
RESULTS:
PLOT:
observing the waveform & display block we get the required output voltage= 11.32V, Load current=10.29A In the observation little bit variation which may due to chemistry of battery & losses
CONCLUSION:
We have Design and simulation of Buck converter for Auxiliary load in EV.
- Input voltage is 48V, Output voltage is 12 V
- Load current is 10A
and also calculate its duty ratio and load (use resistor as load) and also calculate L,C values