Inductor current and Vout ripple plot in Simplis

Buck converter

The Buck converter test bench in Simplis is as shown in Fig. 1.

Fig. 1Buck power stage block diagram^[1]

The Matlab script for plotting the inductor current and Vout ripple is as shown below.

clc; clear; close all;

d = linspace(0.05,0.95,19)*100;

ind_ripple = [242.96164, 457.42, 647.83, 813.73, 954.708, 1070.425, ...
    1160.6, 1225.02, 1263.5214, 1276.02, 1262.4826, 1222.9423, ...
    1157.4937, 1066.2943, 949.5636, 807.584, 640.7, 449.32, 233.9115];

vout_ripple = [30.5, 57.31, 81.026, 101.62, 119.073, 133.3658, ...
    144.4838, 152.4152, 157.1518, 158.69, 157.02, 152.16, ...
    144.1012, 132.8564, 118.4372, 100.8589, 80.14, 56.302, 29.3697];

yyaxis('left');
plot(d, ind_ripple, 'LineWidth',2);
grid on;
xlabel("Duty cycle [%]");
ylabel("Inductor current ripple [mA]");

yyaxis('right');
plot(d, vout_ripple, 'LineWidth',2);
ylabel("Vout ripple [mV]");

The plot is as shown in Fig. 2. From Fig. 2, we can easily tell that the worst case ripple happens at D=50% both inductor current and Vout ripple.

Fig. 2Inductor current and Vout ripple for Buck converter^[1]

Boost converter

The Buck converter test bench in Simplis is as shown in Fig. 3.

Fig. 3Boost power stage block diagram^[1]

The Matlab script for plotting the inductor current and Vout ripple of Boost converter is as shown below.

clc; clear; close all;

d = [10,20,30,40,50,60,65,70, 75, 80,85,90];

ind_ripple = [0.5, 1.0, 1.5, 1.999, 2.498, 2.99705,3.2458, ...
    3.4939,3.740548, 3.984266, 4.220402, 4.430376];

vout_ripple = [119.4992, 235.8, 368.6863, 541.8773, 805.18, 1214.823, ...
    1510.357, 1907.425, 2468.228, 3318.632, 4756.799, 7693.655];

yyaxis('left');
plot(d, ind_ripple, 'LineWidth',2);
grid on;
xlabel("Duty cycle [%]");
ylabel("Inductor current ripple [A]");

yyaxis('right');
plot(d, vout_ripple, 'LineWidth',2);
ylabel("Vout ripple [mV]");

The plot is as shown in Fig. 4. From Fig. 4, we can easily tell that the worst case ripple happens at D=100% both inductor current and Vout ripple.

Fig. 4Inductor current and Vout ripple for Boost converter^[1]

IBB converter

The IBB converter test bench in Simplis is as shown in Fig. 5.

Fig. 5IBB power stage block diagram^[1]

The Matlab script for plotting the inductor current and Vout ripple of IBB converter is as shown below.

clc; clear; close all;

d = [10,20,30,40,50,60,65,70, 75, 80,85,90];

ind_ripple = [0.5, 1.0, 1.5, 1.999, 2.498, 2.99705,3.2458, ...
    3.4939,3.740548, 3.984266, 4.220402, 4.430376];

vout_ripple = [119.4992, 235.8, 368.6863, 541.8773, 805.18, 1214.823, ...
    1510.357, 1907.425, 2468.228, 3318.632, 4756.799, 7693.655];

yyaxis('left');
plot(d, ind_ripple, 'LineWidth',2);
grid on;
xlabel("Duty cycle [%]");
ylabel("Inductor current ripple [A]");

yyaxis('right');
plot(d, vout_ripple, 'LineWidth',2);
ylabel("Vout ripple [mV]");

The plot is as shown in Fig. 6. From Fig. 6, we can easily tell that the worst case ripple happens at D=100% both inductor current and Vout ripple.

Fig. 6Inductor current and Vout ripple for IBB converter^[1]

Conclusion

For Buck converter, the worst case ripple happens at 50% duty cycle case.

For Boost and IBB converter, the worst case ripple happens at 100% duty cycle case.

References and downloads

[1] Fundamentals of power electronics - Chapter 2

[2] Simplis test bench for Buck converter - download

[3] Simplis test bench for Boost converter - download

[4] Simplis test bench for IBB converter - download