SIMULATION MODEL OF BUCK CONVERTER

1. EXPERIMENT NO.1 : SIMULATION OF BUCK CONVERTER USING
MATLAB / SIMULINK
Objective: Design a Buck Converter with appropriate value of parameters and simulate it.
Parameters of the Buck Converter: Input voltage: 24V; Output Voltage: 12V; Output
Power: 100W; Switching Frequency: 100kHz; Ripple in Inductor Current: 25%; Ripple in
Output Voltage: 0.1%;
Theory: Buck Converter is a DC to DC converter (Step down Chopper) having output
voltage is less than input voltage i.e. Vo< Vin
Duty Ratio
D = =
Circuit Diagram and Theoratical Waveforms:

2. Design procedure and final design parameters obtained:
1. Duty Ratio:
D =
So, D=0.5
2. Ripple in Inductor Current:
ΔIL (Theoretical) = 2.08Amp.
ΔIL =
So, L = 28.85µH
where f is switching frequency

3. 3. Ripple in Output Voltage:
ΔVo (Theoretical) = 0.012V
ΔVo =
So, C = 217µF
4. Avg Current through Inductor (Theoretical):
IDC =
IDC = 8.33Amp.
5. Load Resistance:
RL (Fixed) = = 1.44Ω
Results:
1. Simulation Model of Buck Converter:
Here we are taking 100 Samples for each Time period So, Sampling frequency
is 100 times of switching frequency(100kHz).
So, Sampling Time Period = 100nSec.

4. 2. Source Voltage Waveform:
Vin = 24V
Time (sec.)
3. Switching signal to turn ON/OFF to MOSFET:
4. Voltage Across the Diode:
When Diode is OFF
VD = 24 V
When Diode is ON
VD = -0.8V

5. 5. Voltage across the Switch/MOSFET:
When MOSFET/switch is ON
VSW = 0.8V
When MOSFET/switch is OFF
VSW = 24V

6. 6. Current through Inductor:
Avg Current through Inductor (Practical)
IDC = 7.9Amp.
Ripple in Inductor Current (Practical)
ΔIL = 2Amp.
7. Output voltage:
Output Avg. Voltage (Practical)
Vo=11.43V
Ripple in Output Voltage (Practical)
ΔVo = 0.011V