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 20: Buck-Boost Panel with a Resistive Load of 25 ohms

Default Parameters

• Source Voltage: V_DC= 100 V
• L= 100 mH
• C= 400 µF
• Switching Frequency: 1500 Hz
• Duty Cycle: 0.5

Exercise 1: Varying Duty Ratio

Set V_DC to 70 V and switching frequency to 1500 Hz, and vary the duty ratio from 10% to 75% and run the model.

Observe the effect of change in output voltage and measure the average DC load voltage for the corresponding values of duty ratio, and complete the following table with the theoretical average output voltage.

Table 29: Outcome of Varying Duty Cycle

• Compare the observed average output voltage results with the calculated ones.
• For duty cycle = 0.7, what are the values for:
• • Average inductor Current
  • Maximum value of inductor current
  • Minimum value of inductor current
  • Output power (load power)
  • Compare the observed values with the calculated ones and determine the minimum value of inductor () to ensure continuous mode operation.
• What happens If D>0.5 and if D<0.5 (see the effect on the load voltage)?
  Explain.

Exercise 2: Varying Switching Frequency

Set V_DC to 100 V, duty cycle to 0.6 and vary the switching frequency from 1500 Hz to 3600 Hz.

Observe simulation results and fill out the following table.

Table 30: Outcome of Varying Switching Frequency

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

Exercise 3: Varying DC Source Voltage

Set the duty ratio to 60% and the switching frequency to 1500 Hz, and complete the following table for different values of the input voltage.

Table 31: Outcome of Varying DC Source Voltage

• What is the effect of varying DC source voltage on the inductor’s current waveform?
  Explain it.
• Set the V_DC voltage to 120 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 from 100 mH to 50 mH.
Set V_DC to 100 V, duty cycle to 0.6, and C =400 µF.

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

Table 32: Outcome of Changing the Buck-Boost Inductance

• What’s the effect of decreasing the value of the inductance L?
  Hint: Compare to results obtained in Exercise 2.

Exercise 5: Changing Value of C

From the panel, change the capacitance value from C =400 µF to C =800 µF.
Set V_DC to 100 V, duty cycle to 60%, and L=100 mH.

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

Table 33: Outcome of Changing the Buck-Boost Capacitance

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

Exercise 6: Changing Value of R

From the panel, change the resistive load value from R= 25 Ω to R=12.5 Ω.
Set V_DC to 70 V, switching frequency to 1500 Hz, duty cycle to 0.65, 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.