# Centralized MPPT Control Architecture for Photovoltaic Systems Using LoRa Technology
## 2 Centralized MPPT Architecture Based on LoRa
### Power Optimization of PV Systems
#### 2.1.3 Control Techniques  
P&O is a conventional and simple MPPT control method that responds very well under environmental conditions with gradual changes. This algorithm forces a small change in the duty ratio and then looks at the result of this change. If the PV power increases with respect to the previous reading, the sign of the change will be preserved in the next cycle. Conversely, if the PV power decreases, the sign will be changed. However, the response of this algorithm is inconsistent under partial shading and/or abrupt changes in solar irradiance for the reasons explained below. In the case of partial shading, local maxima appear in the \(P-V\) curve, which can lead the algorithm to interpret any of them as the MPP. The case of abrupt changes in irradiance is well known [36]. Figure 4 shows the potential problem, which is known as drifting. Suppose an initial state, Point 1, with \(G_{1}\) irradiance value and the PV module operating at the MPP. Then, the P&O algorithm forces a positive change in the duty cycle, leading to an increase in \(V_{\text{pv}}\) that could coincide with an increase in irradiance to \(G_{2}\). Consequently, power increases due to the greater irradiance (Point 2), but it remains below the MPP that corresponds to the new curve \(P_{\text{max}}(G_{2})\) (Point 4). If irradiance keeps rising, then PV power also increases (Point 3). Therefore, the algorithm proceeds to raise the voltage reference, further deviating from the MPP of the new curve that corresponds to a higher irradiance curve (Point 5). This results in the P&O algorithm that persistently diverges from the real MPP. SMC is a non-linear control methodology that determines control actions based on a defined set of permissible functions. The principal objective of this control approach is to navigate the system along a designated surface within the phase space, encapsulating the  
Figure 4: Illustration of the drifting challenge that the P&O control method faces. desired system behavior. In contrast to conventional continuous control methods, the state feedback control law in SMC does not adhere to a continuous time function. Instead, it smoothly transitions between various continuous control structures that are contingent on the system's position relative to the sliding surface. This inherent characteristic classifies SMC within the realm of variable structure control methods. The operation of SMC unfolds in two discernible phases: the reaching phase and the sliding phase. During the reaching phase, the system systematically approaches the sliding surface through the implementation of a continuous control structure. Subsequently, as the sliding phase initiates upon reaching the sliding surface, the discontinuous controller takes effect, compelling the system states to smoothly slide toward the predetermined set point, which typically corresponds to the origin within the phase space [11; 37]. The error is defined in Equation (9):  
\[e=V_{\text{PV}}-V_{\text{ref}}, \tag{9}\]  
where \(V_{\text{ref}}\) is the voltage reference. This was then calculated, as explained later in Section 2.1.4. The sliding surface \(S\) is determined by Equation (10):  
\[S=e+\lambda\int e\,\mathrm{d}t, \tag{10}\]  
where \(\lambda\) is a design parameter with a positive value (\(\lambda>0\)) that needs to be adjusted during experiments. The SMC control signal has two terms: the equivalent term \(u_{\text{eq}}\) and the switching term \(u_{\text{sw}}\). These terms are described in Equation (11):  
\[u=u_{\text{eq}}+u_{\text{sw}}. \tag{11}\]  
The switching term ensures robustness, as shown in Equation (12):  
\[u_{\text{sw}}=K\,\text{sgn}(s). \tag{12}\]  
The equivalent term is achieved when it meets the \(S=\dot{S}=0\) criterion.