# Grid-Connected PV Systems Controlled by Sliding via Wireless Communication
## 5 Discussion  
There are a large variety of controllers to reach the MPP in PV systems. Linear controllers, such as the Perturb and Observe, the Incremental Conductance or the Ripple Correlation Control [16; 20], are usually simpler and easier than the non-lineal controllers although they are slower under perturbations and cannot guarantee the stability of the system. Amongst the non-linear controllers, e.g., backstepping, neuro-fuzzy, particle swarm optimization, etc. [19; 23], sliding is selected for being a robust control under variations, which it is crucial taking into consideration that wireless data are transferred, causing interferences in the system. Thus, this controller can guarantee stability in the system operation.  
Regarding the communication technology, the Wi-Fi is preferred thanks to the advantages, such as low latency, precise data acquisition and the appropriate range. Thus, the Wi-Fi communication can be used in solar plants where the ZigBee technology is not able to transfer data more than 100 m. In addition, the previous works, using ZigBee or Bluetooth communication [10; 11; 12; 13; 14; 15], are focused on the system monitoring and supervision whereas this work proposed a wireless control besides the monitoring or supervision.  
The communication effects have been verified in this work, corroborating that the system is efficient working wireless, as well as by wire, despite the higher level of noise produced wireless. The response of the grid-connected PV system is robust and stable even when there are sudden changes in the parameters or perturbations. Thus, with abrupt changes of the irradiance, the reference voltage is always achieved with an efficiency higher than 99%. The control signal adjusts itself rapidly, even with sudden changes, in 30 ms. The sliding control is also proper for this system taking into account that it is a discontinuous control and operates better than other controls under sudden changes and interferences produced by the wireless technology.  
In addition, the dynamic of the system is the appropriate. The references values are always reached, and the efficiency of the DC/DC converter varies between 96% and 98.4% and the DC/AC converter from 92,8% to 94.6%. In addition, in a grid-connected PV system, it is essential not disturb the power quality of the grid. In this case, the THD is low, with a value of only 1.9%. The MPPT efficiency is 99%, proving the validity of the system.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Time (s)** & **(0–6.8)** & **(6.8–12.2)** & **(12.2–20)** \\ \hline \multicolumn{4}{c}{DC/DC Converter} \\ \hline \(G\) (W/m\({}^{2}\)) & 921 & 550 & 908 \\ \(V_{in}\) (V) & 17.9 & 18.2 & 17.88 \\ \(I_{in}\) (A) & 2.9 & 1.82 & 2.97 \\ \(P_{in}\) (W) & 51.91 & 33.12 & 53.1 \\ \(V_{o}\) (V) & 56.5 & 55.85 & 56.01 \\ \(I_{o}\) (A) & 0.9 & 0.57 & 0.91 \\ \(P_{o}\) (W) & 50.85 & 32.12 & 50.97 \\ _Efficiency_ & 0.96 & 0.97 & 0.96 \\ \hline \multicolumn{4}{c}{DC/ AC Converter} \\ \hline \(I\)grid & 1.71 & 1.08 & 1.71 \\ \(I\)rms,grid & 1.21 & 0.77 & 1.21 \\ \(V_{\text{rms}}\) & & 39 & \\ \(THD\) & & 1.9 & \\ \(P_{\text{rms}}\) & 47.21 & 30.35 & 47.24 \\ _Efficiency_ & 0.935 & 0.946 & 0.928 \\ \hline \end{tabular}
\end{table}
Table 1: Summary of the values of the experimental case.