## 1 Introduction  
Renewable energy is an important source in microgrids (MGs) [1; 2], as it can help provide power to end users [3]. Power converters (PCs) are used to transfer power from these sources to users and help regulate voltage and improve energy efficiency [2; 4]. The use of PCs in MGs has increased in recent years [5] and some electronic devices are now used to transfer power from alternating to direct current (AC-DC), and from direct to direct current (DC-DC) [6; 7], forming different voltage levels in the network that must be controlled. Although, many stability problems have been studied in AC systems, the PCs can create unstable events in DC systems when the load changes [7]. Thus, this dynamic behavior is of great importance as the development of MGs continues, and better analysis must be performed. Sliding-mode control (SMC) is a specific type of variable structure control (VSC), which was studied extensively during the 1970s. Its widespread use is mainly due to its advantages over parameter variations and tolerance to disturbances [8]. The main feature of VSC is sliding motion, which is when the system state repeatedly crosses certain subspaces or sliding hyperplanes [9]. Moreover, washout filters are extensively used to control chaotic systems and have recently been used in PCs in conjunction with SMC controllers [10]. Some authors have proposed the use of SMC with washout filters [11; 12] as a good option to control the output voltage regarding load variations. The idea when implementing a washout filter in a PC is to ensure some robustness under variations in the constant power load (CPL) via filtering the inductor current. Particularly in [11], nonlinear stability analysis of a standalone DC network and an SMC based on a washout filter is used to maintain constant DC bus voltage. In this case, the authors show the behavior of the system with the controller under nonlinear load variations. Besides, in [12], an SMC with a washout filter is used to regulate the DC bus voltage under constant impedance load (CIL) and constant power load (CPL). They also determined the operating limits of the controlled system in terms of the maximum power drained by the CPL and CIL connected to the bus. In [13], the authors study stability issues in DC MGs with instantaneous CPL, as this load introduces a destabilizing effect in DC MGs that brings significant oscillations of the voltages or reaches system collapse. Some strategies, such as load shedding, addition of resistive loads, filters or energy storage directly connected to the main bus, and control methods, are applied. Commonly, studies do not compare the control performance to different types of loads and, especially, nonlinear CPLs. CPL loads have the characteristic of negative incremental impedance, which may cause system instability during disturbances if the system is not properly controlled [14]. Hence, when feeding a CPL by a buck converter, the results show that the open-loop control is unstable in continuous conduction mode (CCM). Therefore, the system will have additional restrictions on the control in comparison to a purely resistive load [15]. Many techniques have been developed to compensate the system, e.g., damping, small-signal analysis, Lyapunov stability, linearized feedback, droop mode control, filters, vector control, \(d\)-\(q\) frame analysis, and SMC. However, the authors of [16] reveal that there are three stabilization techniques used to compensate the negative impedance of CPL: the Feeder side, intermediate circuits, and load side. On the other hand, the authors of [17] classify the compensation techniques into passive and active damping, space pole placement control, pulse adjustment control, SMC, model predictive control, and feedback linearization. Papers found in the literature show that few studies consider phenomena and parameters present in real systems and do not consider bifurcation diagrams to evaluate the performance of the buck converter.