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This paper presents the design and implementation of a digital control strategy for a Buck converter, used as a solar charger of valve-regulated lead acid (VRLA) batteries. The control system consists of two fuzzy logic controllers (FLCs), which adjust the appropriate increment of the converter duty cycle based on battery state of charge according to a three-stage charging scheme. One FLC works as a maximum power point tracker (FLC-MPPT), while the other regulates the battery voltage (FLC-VR). This approach of using two different set of membership functions overcomes the limitations of the battery chargers with a single control function, where the voltage supplied to the battery is either not constant due to the operation of the MPPT algorithm (possibly damaging the battery) or is constant due to the operation of the voltage control (hence, MPP cannot be achieved). In this way, the proposed control approach has the advantage of extracting the maximum energy of the PV panel, preventing battery damage caused by variable MPPT voltage, thereby extending the battery’s lifetime. Moreover, it allows overcoming of the drawbacks of the conventional solar chargers, which become slow or inaccurate during abrupt changes in weather conditions. The strategy is developed to be implemented in a low-cost AT91SAM3X8E Arduino Due microcontroller. Simulations by MATLAB/Simulink and experimental results from hardware implementation are provided and discussed, which validate the reliability and robustness of the control strategy.

The power produced in a photovoltaic (PV) system is highly dependent on meteorological conditions and the features of the connected load. Therefore, maximum power point tracking (MPPT) methods are crucial to optimize the power delivered. An MPPT method needs a DC-DC converter for its implementation. The proper selection of both the MPPT technique and the power converter for a given scenario is one of the main challenges since they directly influence the overall efficiency of the PV system. This paper presents an exhaustive study of the performance of four step-down/step-up DC-DC converter topologies: Buck-Boost, SEPIC, Zeta and Cuk, using three of the most commonly implemented MPPT techniques: incremental conductance (IncCond), perturb and observe (P&O) and fuzzy logic controller (FLC). Unlike other works available in the literature, this study compares and discusses the performance of each MPPT/converter combination in terms of settling time and tracking efficiency of MPPT algorithms, and the conversion efficiency of power converters. Furthermore, this work jointly considers the effects of incident radiation variations, the temperature of the PV panel and the connected load. The main contribution of this work, other than selecting the best combination of converter and MPPT strategy applied to typical PV systems with DC-DC power converters, is to formulate a methodology of analysis to support the design of efficient PV systems. The results obtained from simulations performed in Simulink/MATLAB show that the FLC/Cuk set consistently achieved the highest levels of efficiency, and the FLC/Zeta combination presents the best transient behavior. The findings can be used as a valuable reference for the decision to implement a particular MPPT/converter configuration among those included in this study.

Este trabajo presenta una completa metodología para el diseño de un sistema fotovoltaico autónomo que maximiza el uso de la energía solar. El método propuesto prioriza la mejor opción en términos de eficiencia en cada etapa del proyecto. Para asegurar el correcto funcionamiento y extender la vida útil de la batería se propone una estrategia de control para el proceso de carga. Resultados experimentales son proporcionados para un sistema fotovoltaico autónomo de baja potencia eléctrica destinado principalmente para la iluminación y electrodomésticos básicos de hogares de bajos ingresos.

In photovoltaic (PV) generation systems, the energy produced is limited by the low efficiency of the solar panels, the variability of weather conditions, and the characteristics of the load connected, so the use of maximum power point tracking (MPPT) methods is essential to maximize the power supplied. Implementing an MPPT requires a power converter as the interface between the PV array and the load, so the converter's behavior is also an important factor to be considered in the overall performance of a PV system. Several MPPT techniques have been proposed over the years, but little literature is still available when required to be compared to the combined performance of different MPPT/converter sets. In this context, the present work presents a comparative study of the performance of three MPPT techniques: constant voltage (CV), perturb and observe (P&O), and incremental conductance (IncCond), acting on two different topologies of DC-DC power converters: Buck and Buck-Boost. Each combination is analyzed considering its transient response and steady-state average efficiency. The study was carried out based on simulations in Matlab/Simulink environment. To obtain more realistic conditions, a model for the commercial PV module Kyocera KC85TS was developed. Results obtained from the PV system operating under various radiation and temperature conditions are compared and discussed, which show that the CV/Buck-Boost combination showed the best transient behavior and that the IncCond/Buck combination had the highest steady-state efficiency.