## 4 Conclusions  
The current research presented an analysis of a real PV system, the objective of which was to track the MPP for performance improvement. Because the atmospheric conditions, such as radiation and temperature, varied throughout each day, non-linearities were reflected within the surroundings.  
Since the results were gathered through real data, an experimental rig was described in which an SG340P PV panel within a boost converter TEP-192 was the main hardware. These were linked to a resistive load, which pretended to simulate external disturbances. The temperature and irradiation, which are influential variables on the system, were acquired through an external sensor. The acquisition of information and the output controlled signal were generated by a dSpace DSP1104, which had embedded designed software to increase the system's performance.  
The first analysis was conducted by way of a resistance change, which provided the characteristic curves of the PV; these represent a useful tool since they define key features for further design. The voltage-current curve was analysed by taking into account the influence of the irradiation and temperature; these variables, reflected in the voltage-power curves, were essential because the MPP showed a dependence based on the irradiation and temperature. Hence, an independence of the irradiation was developed by taking the MPPs in terms of this variable, where a VRE was created by a polynomial approach based on power and temperature.  
In the final step of the experiments, three controllers were designed and tested. The P&O algorithm, commonly used in MPPT, was chosen and implemented despite exhibiting several problems that were pinpointed, such as falling in a local MPP, which is linked to chattering, which in turn leads to an increase of the energy consumption of the system. As a consequence, if the amplitude is sufficiently large (like in the experiments), over-undershoots due to external resistance changes are faded. In a second step, an SMC was embedded with the proposed VRE, where the overshoots were fairly visible and the chattering amplitude was three times lower in comparison to that of P&O.  
However, to improve the chattering reduction, an advanced FLC type-1 was developed and embedded, which produced a significant improvement in comparison to P&O and FLC. The chattering of the controlled voltage decreased by several orders of magnitude and, as a consequence, over-undershoots were unveiled. The contrast in terms of the error with SMC showed that the FLC has a slower correction, although the ripple amplitude is reduced significantly.  
Through this research, future trends for MPPT in PV systems were analysed and will be the objective of forthcoming investigations. These include an analysis of FLC type-2 based on an uncertainty study, which can be contrasted with the present obtained results. Improved P&O algorithms can also be compared in order to search for better chattering management reduction.  
Conceptualization, O.B., M.D. and C.N.; methodology, M.D. and C.N.; software, C.N.; validation, M.D.; formal analysis, O.B., M.D. and C.N.; investigation, O.B. and C.N.; resources, O.B.; writing--original draft preparation, C.N.; writing--review and editing, O.B., C.N. and M.D.; supervision, O.B.; project administration, O.B. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Basque Government, Diputacion Foral de Alava and UPV/EHU, respectively, through the projects EKOHEGAZ (ELKARTEKKK-2021/00092), CONAVENTER and GIU20/063.  
Not applicable.  
The authors would like to express their gratitude to the UPV/EHU, the Basque Government and the Diputacion Foral de Alava.  
The authors declare no conflict of interest.