## 7 Conclusions  
This paper proposes a new solution for the first stage of a PV microinverter, which enables the reduction of the DC-link capacitor to non-electrolytic values, thus improving the system reliability. This solution is based on the NEC boost converter and an SMC, providing a precise design process for the complete solution. The NEC boost converter provides continuous input and output currents, similar to the Cuk converter, but without the voltage inversion, hence simplifying the sensing circuits. Moreover, the proposed PV system imposes lower stress in the internal capacitor and input inductor in comparison with the Cuk converter. The continuous current condition provided by the NEC converter could be also useful to design battery chargers/dischargers, since high-frequency current harmonics affect both the battery health and the DC bus power quality. In addition, the voltage conversion ratio is the same one obtained with a boost converter; hence, the NEC boost topology can be used to replace classical boost converters in existing applications. This could improve the overall efficiency because the RMS current provided by the NEC boost converter is lower than the RMS current provided by the classical boost option, which reduces the ohmic losses on the elements of the second stage. Despite the additional complexity of the NEC boost converter, the paper presents a detailed modeling set formed by the switched model, the averaged model, and the steady-state relations. Those models can be used to design new control strategies for the proposed first PV stage. The global stability of the proposed SMC was mathematically demonstrated, which enables the first stage to be used in any operation condition including fast-changing irradiance. Moreover, this SMC enables the proposed PV system to be scaled to any power level. However, the dynamic limitation introduced by the reachability conditions must be taken into account in the design; thus, a prior knowledge is needed of the fastest irradiance change to be experimented. This aspect was taken into account in the step-by-step design procedure proposed for the PV system. The implementation of the proposed control system mixes both analog and digital circuits, which provides flexibility to include additional features such as diagnostic algorithms or more complex MPPT algorithms. In fact, one future improvement is to study the inclusion of MPPT algorithms designed for partially shaded PV systems, which could improve the microinverter's flexibility by enabling the connection of small PV arrays. In any case, the results obtained in the circuital simulations were satisfactory, since all the theoretical predictions were confirmed with realistic and non-linear simulations. Those results provide confidence to the proposed solution, since the commercial power electronics simulator has been also adopted to validate other microinverters reported in literature. However, the experimental implementation of the proposed first stage will have some challenges that must be addressed in future developments. For example, the resolution of the comparator used in the switching circuit could modify the switching frequency; thus, a safety margin must be introduced into the calculation of the hysteresis width. Another implementation problem to face is the tolerances of the electronics devices; thus, safety margins on the ripple requirements must be also introduced. The largest implementation problem will be the microprocessor interface with the analog circuitry, since the resolution of both the ADC and DAC will introduce errors into the switching function calculation: 10-bit resolution (usually provided in microcontrollers at 5 V) could introduce 4.9 mV errors, which is half of the PV voltage ripple; instead, the suggested microprocessor TMS320F28335 has 12-bit resolution, which only introduces 1.2 mV errors, but at a higher cost in comparison with a traditional microcontroller.