In the panel, choose from the menu Pre-Selected: Resistive Load and select the 25 ohms as resistive load value for exercises 1 to 5.

Figure 14: Buck Panel with a Resistive Load of 25 ohms

Default Parameters

• Source Voltage: V_DC= 100 V
• L= 100 mH
• C= 400 µF
• Resistive load (R= 25 Ω)
• Switching Frequency: 1500 Hz
• Duty Cycle: 0.5

Exercise 1: Varying Duty Ratio

Set V_DC to 300 V and switching frequency to 1500 Hz and vary the duty ratio from 10% to 90% and run the model.
See the effect of change in output voltage and measure the average DC load voltage for the corresponding duty ratio values, and complete the following table with the theoretical average output voltage.

Table 17: Impact of Varying Duty Cycle

• What effect will a duty ratio at the buck converter have on the voltage output? Explain.
• Compare the observed average output voltage results with the calculated ones.
• For duty cycle = 0.6, what are the values for:
  • Average inductor current
  • Maximum value of inductor current
  • Minimum value of inductor current
  • Ouput power
  • Compare the observed values with the calculated ones and determine the minimum value of inductor () to ensure continuous mode operation.

Exercise 2: Varying Switching Frequency

Set V_DC to 300 V, duty cycle to 0.5 and vary the switching frequency from 1500 Hz to 3600 Hz.
Observe simulation results and complete the following table.

Table 18: Impact of Varying Switching Frequency

• What is the effect of change in the frequency on the inductor current?

Exercise 3: Varying DC Source Voltage

Set the duty ratio to 50% and the switching frequency to 1500 Hz, and complete the following table for different values of the input voltage:

Table 19: Impact of Varying DC Source Voltage

• What is the effect of varying DC source voltage on the inductor’s current waveform?
  Explain it theoretically.
• Set V_DC voltage to 350 V, switching frequency to 1500 Hz and duty cycle to 0.5, calculate the theoretical values of input and output powers and compare them with the observed ones.
  What do you conclude?

Exercise 4: Changing value of L

From the panel, change the inductance L_buck from 100 mH to 50 mH.
Set V_DC to 300 V, duty cycle to 0.5, and C =400 µF.

Vary the switching frequency from 1500 Hz to 3600 Hz.
Observe simulation results and complete the following table:

Table 20: Impact of Changing the Buck Inductance

• What is the effect of decreasing the value of the inductance L_buck?
  Hint: Compare to results obtained in exercise 2.

Exercise 5: Changing Value of C

From panel, change the capacitance value from C =400 µF to C =800 µF.

Set V_DC to 300 V, duty cycle to 0.5 and L=100 mH.
Vary the switching frequency from 1500 Hz to 3600 Hz.
Observe simulation results and complete the following table:

Table 21: Impact of Changing the Buck Capacitance

• What is the effect of changing the value of the capacitor?

Exercise 6: Changing Value of R

From panel, change the resistive load value from R= 25 Ω to R=12.5 Ω
Set V_DC to 300 V, switching frequency to 1500 Hz, duty cycle to 0.5, L=100 mH and the capacitance as C=400 µF.

• What is the effect of decreasing the resistive load value on the load current, inductor current, load voltage, and output power?
  Explain your observations.