*6.1. Sliding Mode Parameter Choice*

The performance of the conceived sliding mode controller depends on the discontinuous term coefficient. A simulation study was carried out to determine the best choice of this factor. Figure 7 shows the obtained results. It should be noted that high sliding mode parameters lead to reduced response times both for the system and the controller outputs as shown in the zones 1 to 4. On the other hand, it increases the magnitude of oscillation both in the controller and the system responses, which may lead to disrupting the system. Thus, in this work, the considered parameters are chosen in such a way that a compromise between rapidity and stability is achieved.

**Figure 6.** Closed loop control of buck control using sliding mode control approach.

**Figure 7.** *Cont*.

**Figure 7.** Discontinuous function coefficient effect: (**a**) evolution of M coefficient, (**b**) evolution of the control voltage and (**c**) evolution of the output voltages.

#### *6.2. Controller's Behavior under Abrupt Target Output Voltage Variations*

In this case, the aim is to test the tracking behavior of the proposed sliding mode controller against abrupt target output voltage variations. All five algorithms are implemented and simulated in the same test conditions. In fact, the load resistor, the input voltage, and the DC-DC buck converter parameters are all maintained at their nominal values. The target output voltage is first fixed at 150 v. At t = 0.03 s, it changes to 350 v and decreases to 250 v at t = 0.07 s. The five obtained output voltages and control signals are respectively reported in Figure 8a,b. Comparative performances are extracted and summarized in Table 3.

**Figure 8.** Target output voltage variation: (**a**) evolution of the control voltage and (**b**) evolution of the output voltages.


**Table 3.** Comparative study between the five algorithms.


#### **Table 3.** *Cont.*
