## 1 Introduction
### Literature Review  
This subsection discusses different approaches, reported in literature, to face the previous considerations. The microinverter reported in [8] adopts a DC/DC boost converter for the first stage, which provides the boosting factor needed to match the PV voltage and the DC-link voltage. The first stage has no high-frequency controller; hence, the boost converter can be perturbed by the low-frequency oscillations present in the DC-link, and no global stability of the first stage is ensured. Finally, this solution adopts an incremental conductance (INC) MPPT algorithm. The microinverter presented in [12] is also based on an open-loop boost converter with no global stability ensured; however, in this case, a large electrolytic capacitor is used to reduce the DC-link voltage oscillations at the expense of reliability; finally, the perturb and observe (P&O) MPPT algorithm is used to maximize the power production. The work reported [14] also considers a grid-connected PV system; the first stage of this solution is formed by a boost converter in open-loop with a capacitive DC-link, where the duty cycle is defined by a predictive MPPT algorithm. In this case, the voltage oscillations at the DC-link are mitigated by using a three-phase inverter, which requires balanced power flows in each phase to ensure a small oscillation magnitude. Since three-phase networks are not common in urban/residential power systems, this solution is restricted to industrial environments. Finally, the design of the power stage is not discussed. Another approach is reported in [9], where a flyback converter is adopted. The first stage of this solution includes a sliding-mode controller (SMC) to mitigate the DC-link voltage oscillations, thus avoiding the need for large electrolytic capacitors. However, the flyback converter requires the use of a high-frequency transformer, which introduces electromagnetic pollution that could affect the sensors of the system. Instead, the work reported in [15] adopts both the boost converter and SMC into the first stage to ensure stability. The SMC is designed considering a resistive load to simplify the analysis. Despite changes on the resistive load being considered, such an approximation does not correctly represent the input of a grid-connected inverter; thus, no global stability can be ensured. In addition, the boost converter design is not analyzed; thus, no guidelines concerning the design of the passive elements are provided. Similar problems are found in [11], where an SMC is designed for the boost converter in the first stage, ensuring stability of both the converter and P&O MPPT algorithm, but the design of the power stage is not discussed. The work reported in [16] succeeds in providing design equations for the first-stage converter (with a boost topology). As in the case of [15], a resistive load model is used to represent the second stage; thus, those results are not easily applicable to real PV microinverters. Moreover, the work reported in [16] adopts a robust-direct-adaptive controller (RDAC), but the calculation of the controller parameters is not discussed. Finally, an MPPT algorithm similar to the P&O solution is adopted. The work discussed in [13] is also based on a boost converter, where the first stage is regulated using a mixed proportional-integral (PI)-P&O controller, but the system stability is not formally analyzed. Moreover, the converter design is not discussed. The solution reported in [17] is also based on a boost converter and an SMC; however, in this case, an additional PI controller is introduced. The main advantage of this solution is the use of a particle swarm optimization (PSO) to obtain the optimal controller parameters; however, the converter design is not discussed and the global stability of the system is not formally demonstrated. Finally, the work reported in [18] presents a first stage based on a boost converter controlled by an SMC and a P&O algorithm.