## 3 MPPT Techniques
### On-Line MPPT Techniques  
Generally, the instantaneous values of the PV attempt output voltage or current are used to generate the control signals in online MPPT systems. A modest, methodical, and predetermined perturbation in the PV system's voltage, current, or duty cycle is applied, together with the generated control signal, to determine the output power. The direction of change (increase or decrease) in the control signal is determined by analyzing how the PV panel's output power responds to perturbation. These MPPT methods track MPP without any prior empirical information. Additionally, these methods are precise at varying temperatures and irradiances. Hill-climbing (HC), perturb and observe (P&O), and incremental conductance (IC) approaches are just a few of the MPPT methods that fall under this category [102]. P&O is the most widely used MPPT technique due to its simplicity and convenience in implementation [103, 104]. In this technique, the output voltage of the PV panel is measured and perturbed by a small change, which causes a change in power (\(\Delta P\)), as provided in Table 2. According to Table 2, the P&O technique works by perturbing the PV operating voltage decrease and increase, as shown in Figure 8. For every perturbing cycle, the PV output power is measured and compared. Through the perturbation process, the following can be noted:  
If \(\Delta\)P = 0, the system is working at the MPP and the voltage for the next sample remains constant. If \(\Delta\)P > 0 and \(\Delta\)V > 0, then an increment is added to the operating voltage value to approach the MPP. If \(\Delta\)P < 0 and \(\Delta\)V > 0, then the decrement is added to the operating voltage value to approach the MPP. If \(\Delta\)P < 0 and \(\Delta\)V < 0, then an increment is added to the operating voltage value to approach the MPP. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **MPPT** \\ **Technique** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Parameter** \\ **Dependency** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Control** \\ **Variable** \\ \end{tabular} } & \multicolumn{2}{c}{**Circuitry**} & \multirow{2}{*}{\
\begin{tabular}{c} **Parameter** \\ **Tuning** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Tracking** \\ **Accuracy** \\ \end{tabular} } & \multirow{2}{*}{**Efficiency**} & \multirow{2}{*}{**Complexity**} \\ \cline{3-3} \cline{5-6}  & & **V** & & & & & & \\ \hline CF & Yes & ✓ & & ✓ & & Yes & Medium & Complex \\ Lookup table & Yes & ✓ & ✓ & & ✓ & No & Low & Medium & Complex \\ Pilot cell & Yes & ✓ & & ✓ & ✓ & No & Low & Low & Simple \\ FSCC & Yes & & ✓ & ✓ & ✓ & No & Low & Simple \\ FOCV & Yes & ✓ & & ✓ & No & Low & Simple \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A comparison of various offline MPPT methods. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Perturbation (\(\Delta\)V)** & **Change in Power (\(\Delta\)P)** & **Next Perturbation Direction** \\ \hline \(\Delta\)V > 0 (Positive) & \(\Delta\)P > 0 (Positive) & Positive \\ \(\Delta\)V < 0 (Negative) & \(\Delta\)P > 0 (Positive) & Negative \\ \(\Delta\)V > 0 (Positive) & \(\Delta\)P < 0 (Negative) & Negative \\ \(\Delta\)V < 0 (Negative) & \(\Delta\)P < 0 (Negative) & Positive \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Perturb and observe methodology. In the P&O algorithm, a constant steady-state oscillation occurs at MPP, since the perturbations continuously change direction to retain the MPP under quickly varying solar irradiance, which decreases system efficiency and raises the losses in output power [103]. In terms of operating theory, the hill climbing (HC) technique is similar to the P&O approach; the only difference is the perturbation parameter. For MPP tracking, the P&O senses and perturbs the current or voltage, whereas the HC perturbs the duty cycle [21]. The output trade-off between the dynamic and steady-state response error is a common issue in both methods.