**3. Maximum Power Point Tracking (MPPT) Methods for Partial Shading**

PV arrays consisting of several panels are the most basic units of any PV system. Based on the I–V curve depicted in Figure 3, the PV operating point can vary from zero to the open circuit voltage. The operating point varies with the load variation and does not always stay at the maximum power point. A unique maximum power point (MPP) operating point exists in the I–V and P–V curves for every irradiation and temperature. This point keeps shifting when any atmospheric change occurs [98,99]. Thus, maximum power point tracking (MPPT) controllers are designed to keep tracking MPP, and they form an integral part of PV systems. Figure 3 also depicts the maximum operating point, *Pmp*, *Vmp*, and *Imp,* for a PV panel. In a uniform insolation case, the total maximum output power of a PV array is equal to the sum of the maximum power values of all individual modules.

**Figure 3.** Maximum power point characteristics for I–V and P–V curves.

A significant impact on the operation of PV modules is shading caused by cloud cover, trees, or buildings. When one or more of the modules in a solar panel comes under the effect of shading, the module voltage drops causing it to work as a load rather than as a generator, and this causes a hot spot problem [100–102]. Each PV module is equipped with a bypass diode to overcome the hot spot formation. However, adding the bypass diode creates multiple peak points in the P–V curve.

Among the multiple peaks, one is the global maximum power point (GMPP) and the others are local maxima power points (LMPPs). Multiple maximum points can confuse traditional MPPT schemes as they can easily track and settle at a local maximum, which reduces the available power output from the PV array. A reliable technique is required to track the GMPP appropriately [103–105]. Conventional MPPT techniques cannot identify the GMPP under partial shading conditions (PSC) and usually track local peaks reducing the generated power from the PV system.

Figure 4 shows a PV module where PV modules 3 and 4 are shaded in Figure 4b due to environmental conditions. The bypass diodes provide an alternate path for the current flow, creating multiple peaks. The P–V curve shown in Figure 5 depicts the numerous maxima during PSC. Modern soft computing MPPT techniques are developed to track the GMPP as the conventional methods fail to differentiate between the GMPP and the LMPPs [106–108]. The MPPT methods for partial shading mitigation techniques will be explained in detail in the next section.

**Figure 4.** PV modules: (**a**) no shading and (**b**) modules 3 and 4 are shaded.

**Figure 5.** PV array output power characteristics under normal and partial shading.

#### **4. Dynamic Tracking under Partial Shading**

Partial shading reduces the overall efficiency of the PV system. To generate the maximum available power from the PV system under this non-uniform environmental condition, partial shading mitigating techniques are essential for the PV system working in grid-connected or standalone modes. Conventional MPPT methods have fixed step sizes and usually become trapped in local peaks, and they fail to dynamically track the MPP under partial shading conditions.

Partial shading mitigation techniques are broadly classified into two major groups. The first group includes all the MPPT-based methods, which have been further classified into modified conventional, soft computing, and hybrid techniques, and the second group comprises circuit-based topologies. The classification of MPPT techniques under partial shading is provided in Figure 6. The conventional MPPT methods under uniform irradiation, such as P&O, IC, and HC, are thoroughly discussed in the literature and will not be covered in this paper. This section provides MPPT techniques under partial shading conditions.

**Figure 6.** Classification of different MPPT schemes for shading mitigation.
