## 3 MPPT Techniques
### On-Line MPPT Techniques
This issue is more serious in the HC method, since it controls the duty cycle instead of voltage, while in the P and O method, voltage is regulated directly. Furthermore, due to a constant duty cycle, the traditional HC approach fails to extract the MPP efficiently under changing climate conditions [21]. The slope of the PV curve is discovered using INC, which is driven by Equations (10)-(12). Equation (10) determines if the PV module's operating point is at its MPP, as shown in Figure 9. On the other hand, Equations (11) and (12) operate at the right and left sides of the unique operating point on the PV curve, respectively, to achieve the MPP by varying the duty cycle of the INC algorithm presented in Table 3[22]. \[\frac{dI}{dV} =-\frac{I}{V} \tag{10}\] \[\frac{dI}{dV} <-\frac{I}{V}\] (11) \[\frac{dI}{dV} >-\frac{I}{V} \tag{12}\] \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mode** & \multicolumn{2}{c}{**Perturbation**} & **MPP Level** & **Status** \\ \hline
**Mode-I** & \(\frac{dP}{dV}=0\) & \(\frac{dI}{dV}=-\frac{I}{V}\) & At MPP & Hold \(V_{PV}=V_{MPP}\) \\
**Mode-II** & \(\frac{dP}{dV}>0\) & \(\frac{dI}{dV}>-\frac{I}{V}\) & Left side of MPP & Increase the voltage until \(V_{PV}=V_{MPP}\) \\
**Mode-III** & \(\frac{dP}{dV}<0\) & \(\frac{dI}{dV}<-\frac{I}{V}\) & Right side of MPP & Decrease the voltage until \(V_{PV}=V_{MPP}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: INC algorithm. Figure 8: P-V curve with P&O operating principle. The scheme that involves Equations (10)-(12) assumes the slope of the \(PV\) curve at MPP is equal to zero, as shown in Equation (13). \[\frac{dP}{dV}=0 \tag{13}\]  
Consequently, Equation (13) can be rewritten as  
\[\frac{dP}{dV}=\frac{d(I\times V)}{dV}=V\frac{dI}{dV}+I\frac{dV}{dV} \tag{14}\]  
\[\frac{dP}{dV}=V\frac{dI}{dV}+I \tag{15}\]  
This implies that  
\[\frac{dI}{dV}+\frac{I}{V}=0 \tag{16}\]  
One of the most often employed MPPT strategies is INC, along with P&O [22]. Nevertheless, in INC, the slope of the PV curve affects the duty cycle in either fixed or variable step sizes until the MPP is reached. These MPPT approaches employ a set step size, unlike the INC, HC, and P&O methods, whose process is dependent on the reference voltage's step size. The controller can quickly reach the MPP with large steady-state oscillations by using a large step size. If not, reduced steady-state oscillations will occur with moderate convergence speeds for small step sizes, while the MPP for rapidly varying irradiance will be lost. Due to this, many modifications to the P&O MPPT method based on the P-V curve have been presented. However, they are thought to provide insufficient solutions for dealing with these issues. [PERSON] et al. [105] presented the current sweep (CS) method based on MPPT for the PV system. The I-V curve of the module/panel is drawn using the module's established operating conditions in the current sweep method. This approach extracts the current and voltage and manipulates them as a fixed function of time, as expressed in Equation (17). \[i\left(t\right)=f\left(t\right) \tag{17}\]  
Since the current sweep method deals with the PV current and interprets the PV system's I-V curve to evaluate the MPP, the MPP tracking cannot be achieved continuously. This approach is only used when the change in the calculated power is greater than a fixed threshold, which would be between 5% and 10% of the PV system's maximum power. The meaning of the threshold cannot be too high or low. The current sweeping would be rarely performed if the threshold is set too high. The current sweeping would be near  
Figure 9: P-V curve of the PV system and signs of its slope at various regions. continuous if the current is too minimal. Until the next current sweep, when the new MPP is calculated, the current sweep controller keeps the calculated voltage as the PV panel operating voltage [105]. The online methods also include the extremum seeking control (ESC) method and ripple correlation control (RCC) method. [PERSON] and [PERSON] [106], [PERSON] et al.