# PV Tracking Design Methodology Based on an Orientation Efficiency Chart
## 2 Materials and Methods
### Selection of the Control Technique and Device Programming  
The control technique (e.g., Grafcet, Petri Nets, Neural Networks, or Diffuse Logic) is selected based on the process to be performed, while considering the detailed description of the solar tracker prototype operation (Step 4) and the control device. The latter could be a field programmable gate array (FPGA), programmable logic controller (PLC), microcontroller, or industrial personal computer (PC), based on the previously selected technique. Finally, a program is developed for the algorithm and control technique previously established in Steps 4 and 5. According to the data previously obtained to fulfil the design requirements of minimizing the amount of movement and utilizing \(\pm 30^{\circ}\) windows for maximum efficiency, a general time tracking system with an open-loop control with both automatic and manual control is proposed (Figure 7).  
The device that will be installed on the solar tracker to perform the proposed control of A1 and A2 (DC gear motor) must be selected. A controller with the capacity to manage dates and hours and perform some arithmetic operations is required. An FPGA, a PLC, a microcontroller, and an industrial PC are considered and compared in Table 4.  
Figure 6: Illustration of selected actuators.  
Figure 7: Proposed solar tracking control.  
One feasible option for the development of the control system is a system based on a microcontroller combined with an H bridge due to its low cost and high availability; however, FPGA boards are equally feasible. The selected control system is used to perform basic arithmetic operations and to facilitate the incorporation of a manual alignment system for the installation of the solar tracker, based on the schematic diagram shown in Figure 8.  
According to the design methodology, it is necessary to program the microcontroller with an adequate technique. As detailed in Table 5, before developing the controller circuit, the control technique must be selected based on its characteristics and operation of the solar tracker prototype mentioned in the previous step.  
The Grafcet technique is selected, as it facilitates programming sequences of transitions defined by a change of states and its simplicity allows the expansion of the program code for a solar tracker. In addition, the developer has a large amount of knowledge in applying this technique. Figure 9 illustrates the Grafcet technique used to develop the program of an algorithm that follows the trajectory of the sun along three points separated by 60\({}^{\circ}\) along the azimuth axis (Figure 5) using the low-cost microcontroller selected in the previous step that has limited digital I/O and the capacity to perform basic arithmetic operations and manage the date and time.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Device** & **Cost** & **Availability** & **Maintenance** \\ \hline Diligent field programmable gate array (FPGA) for Linux & L & H & L \\ Arduino microcontroller & L & H & L \\ Festo (programmable logic controller (PLC)) compact unit control & M & M & H \\ Industrial personal computer (PC) with output interfaces & H & L & L \\ \hline \hline \end{tabular}
\end{table}
Table 4: Control device selection matrix.  
Figure 8: Controller connection schematic diagram.  
The tracking begins at point P1, located 30\({}^{\circ}\) above the azimuth axis, and the tracker remains at this point until 10:00. One minute later, the tracker moves to point P2, which is located 90\({}^{\circ}\) above the azimuth axis from the previous point, due to the activation of actuator A1, and the tracker remains at this point until 14:00. At 14:01, the tracker moves to point P3, which is located 60\({}^{\circ}\) from the previous point, due to the activation of actuator A1, and it remains at this point until 18:00. Finally, one minute after 18:00, the tracker returns to point P1 by activating the actuator A1 to turn 120\({}^{\circ}\) in the opposite direction.