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Maximum power point (MPPT) is an integral part of grid connected photovoltaic (PV) systems. Nowadays, many studies have been devoted in order to enhance the performance of PV systems through developing new or improving already existed MPPT methods.
Normally, the conventional MPPT methods that includes Perturb and Observe (P&O), Incremental Conductance (IncCond), and Hill Climbing (HC) techniques, are able to track the maximum power point (MPP) and usually can achieve 99% or higher tracking efficiency (Ahmed, 2008; Esram, 2007; Hohm, 2000; Sera, 2006). The P&O is the most used for its simplicity. The system is continuously perturbed in order to reach the MPP (Zegaoui et al., 2011). Tough, the mission becomes more problematic when the PV array experiences partial shading (PS) conditions and extracting the maximum becomes a challenging task because of the non-linearity of the Power-Voltage (P-V) curve, which exhibits multiple local peaks. In fact, the half or more of the PV array receive different amount of insulation because of partially cloudy conditions caused by towers, clouds, trees, neighboring, etc. (Wasynezuk, 1983; Chowdhury, 2010; White, 2016). Thus, it is imperative to use a suitable MPPT technique which tracks the unique global peak (GP) of the shaded PV array effectively, fast and smoothly (Koutroulis & Blaabjerg, 2015). In the latter case, conventional MPPT techniques become ineffective and inaccurate because they cannot discriminate between global and local peak and they can be trapped on the first local peak which reduces the effectiveness of the whole system (Liu, 2012; Shaiek, 2013; Quaschning, 2008). Thus, the main target of this work is the study of those difficulties and limitations of the conventional methods such as P&O and introducing a more suitable method based on Evolutionary techniques (ET) mainly the Genetic Algorithm (GA) and the dynamic Particle Swarm Optimization (PSO).
The partial shade raises the power consumption and the maximum power of the partially shaded PV modules is minimized. To overcome these issue, a bypass diode is often included in parallel with each serial connection of PV cells which makes the P-V characteristic develop multiple maxima. Figure 1 shows the difference between the MPPs in a totally sunny module and a shaded one where the global and the local MPPs are indicated.
Figure 1. Example of the power-voltage characteristics of a PV array