PV-Battery Hybrid System with Less AH Capacity for Standalone DC Loads

Abstract

Abstract Partial Shading Condition (PSC) is one of the key issues faced by Solar Photovoltaic (PV) systems. PSCs mainly occur due to clouds, shadows of trees/buildings, dust and so on. During the PSC, the shaded PV module acts like a sink and absorbs the power from highest irradiated modules in a string and leads to hotspot. This situation is highly vulnerable and has to be avoided. Bypass diodes are used in series configured PV modules to overcome the hotspot effect caused due to PSC. However, the use of bypass diodes leads to multiple peaks in the Power-Voltage (P-V) graph of a PV array. One among them is Global peak point, where PV array needs to operate under PSC. In such a case, some amount of power generated by the shaded modules gets wasted, which will lead to poor performance and efficiency of the overall system. Moreover, for standalone DC load applications an auxiliary supply also required to provide reliable supply to the load during night times and PSC. Normally, batteries are used in standalone systems as an auxiliary supply. To control the charging and discharging process of battery a bi-directional DC-DC converter is used as a charge/discharge controller. The amount of power that is being charged/discharged by batteries depends upon the load requirement and solar power availability. Under PSC, due to lack of extraction of PV power from shaded modules, batteries have to supply the deficient power to the load. This situation forces to increase the AH capacity of the battery to provide reliable supply. In this research article PV-Battery Hybrid system is proposed to improve the performance of PV under varying irradiance and load conditions with reduced AH capacity of battery for standalone DC loads. The performance assessment of proposed topology has been carried out with the comparison of percentage improvement in power extraction, percentage reduction in the average current consumption of battery and SoC delivered by battery with conventional methodologies of bypass diode and proposed methodology under PSC. The assessment is carried out on MATLAB/SIMULINK and results are presented.