The intermittent nature of photovoltaic energy necessitates the incorporation of storage devices to ensure the continuality of loads feeding. In addition, it is important to model, control, and verify the operating of the designed system before implementation. Furthermore, the integration of power electronic interfaces plays a significant role in protecting the system and benefiting from solar energy. To this end, a buck converter is chosen to charge the battery and supply the supercapacitor. The control strategy is based on the maximum power point tracking techniques when the management algorithm recommends MPPT function mode. Otherwise, a feedback constant voltage PI controller is designed. Indeed, perturb and observe and incremental conductance are implemented and compared to analyze the system efficiency within the management strategy to charge the battery, switch between the controllers, and feed a supercapacitor in case of full battery charge. The obtained results using MATLAB/SIMULINK platform confirm the behaviour of the proposed strategy.
TopIntroduction
Solar activity is the main source of renewable energy sources. The earth receives an energy capacity of the order of 1.8×1014 MW per year, which is several thousand times higher than the actual electricity consumption. So, solar energy can meet our current and future energy needs (Sheina,2019).
The global power growth of renewable energies made its investigation competitive with conventional fossil fuel sources. According to the statistics of 2017, the added capacity for solar energy is 98GW and is about 52GW for wind energy, however gas and coal grown only with 38GW and 35GW, respectively. According to the same statistics, the investigation in solar photovoltaic energy has increased significantly and taken the top of development and installation compared to the other renewable energies with 32%, followed by wind energy by 10%. China takes the head of global PV energy installation with 23%, followed by the USA with 14%, Japan with 13%, Germany with 13%, Italy with 6%, however, the rest of the world takes only 30% of the total PV installations (Ahmad,2020).
It is worth mentioning that thanks to the French scientist Edmund Becquerel, the conversion of solar electromagnetic radiation into electricity (i.e. known as the photovoltaic effect) has been successfully conducted in 1839 (Lofthouse,2015).
In the recent few years, large installations of PV systems have been realised due to the availability of solar energy all around the earth and the development of new solar cell technologies. In addition, the decrease in the PV technologies and PV equipment prices, the increase in the power efficiency encouraged investigators to explore more and more solar energy to produce electricity. Moreover, Photovoltaic Generators (PVGs) do not contain any mechanical parts that emit noise when generating electricity. This makes the PV system the most suitable for buildings and residential cities (Jha, 2017).
To get high performance with Solar Photovoltaic energy, it is important to well design the installation components and controllers. During the last decades, researchers proposed several solutions to enhance the extracted, transferred, and supplied energy and guarantee its continuality, decrease costs, and ensure the reliability of the system. To this end, diverse materials technologies are tested and used to constitute the PV cell which differs on the efficiency of conversion, costs, and robustness, such as, mono and poly Crystalline Silicon (C-Si), Thin Film, Cadmium Telluride (CdTe), Copper Indium Gallium Selenide (CIGS) technologies (Konagai,2011; Guha,2000). In fact, a Small power value is obtained from the solar cells. So, a combination of several cells in series or parallel is important to generate a required power value. This connection forms a solar module or namely a PV panel (Ngyen,2008). The series combination of several panels constitutes the PV string, while, the parallel connection of strings constitute the PV array. In fact, the number of series-connected modules depends on the required voltage value, while, the number of parallel-connected strings is related to the required output current. It is well known that the obtained current-voltage (Ipv, Vpv) and Power-voltage (Ppv, Vpv) curves at the PVG terminals had a non-linear form, moreover, the direct connection of the module to load is not beneficial for the installation since no protection is presented and the power generated by the PVGs has an intermittent and non-linear nature (Mohmoud,2006). In practice, power electronic devices (converters and inverters) are incorporated between the PVGs and loads to deal with such troubles. The choice of Power devices to use depends on the load requirement. For instance, if the installation contains AC-loads the single-phase, three-phase, or multilevel inverters are required to transfer the DC generated current to an AC form (Kasper,2013). Else, if the installed loads are of DC nature, a DC-DC converter is sufficient to feed them with the desired DC power (Behjati,2014). The DC-DC converters may be divided into three large categories which defer on the manner that the magnetic elements are maneuvering, arranged, and controlled. These DC-DC power converters consist of an inductor, a capacitor, and a switching device (IGBT, MOSFET,...), that transfer a DC voltage to a different form of DC voltage by stepping it down or up depending on the designed system, and which are: (1) DC-DC buck (step down) converters: which give a low voltage value at their terminals. (2) DC-DC boost (step-up) Converters: permits high voltage at the loads' side. Whereas, the DC-DC buck-boost (step-up/ step down) converters provide high or low voltage value depending on the load requirement (Li,2008; Coelho,2009).