# Efficient Wireless Monitoring and Control of a Grid-Connected Photovoltaic System
## 2 System Architecture Overview  
Figure 1 shows the two-stage, grid-connected wireless PV system. It consists of PV modules connected to a DC/DC converter that transfers the energy to the grid through a DC/AC converter. It has two main building blocks--a wireless grid-connected PV system (WGPVS) that links with a wireless centralized control system (WCC). More specifically, the WGPVS is composed of several wireless smart photovoltaic systems (WSPS) connected to a wireless conversion unit (WCU). Then, there are different WGPVSs connected to the AC bus to transfer all the energy provided by the PV modules to the power grid. The WCC includes the coordinator node that controls all the WGPVSs. Both DC/DC and DC/AC converters are connected to a wireless sensor network where data collected by motes are periodically transmitted to the coordinator node through wireless communication. Then, two control strategies are applied in parallel to generate the required signals for the converters, optimizing the energy conversion of the overall system.  
The WSPS includes PV arrays connected to boost converters and wireless sensor network nodes. The boost converter is responsible for managing the MPP of each PV array. For this purpose, the boost converter is connected to the sensor node, which gathers the signals of the required parameters and sends them to the coordinator node. Then, the WCC provides to the sensor node the control signal for the DC/DC converter. Finally, each DC/DC converter is connected to the DC bus to transfer the energy.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Symbols** & **Description** \\ \hline MPP & maximum power point \\ MPPT & maximum power point tracking \\ WSN & wireless sensor networks \\ WGPVS & wireless grid-connected PV system \\ WCC & wireless centralized control \\ WSPS & wireless smart photovoltaic system \\ WCU & wireless conversion unit \\ CCM & continuous conduction mode \\ GTS & guaranteed time slot \\ BO & Beacon Order \\ SO & Superframe Order \\ \hline \hline \end{tabular}
\end{table}
Table 1: List of symbols with their descriptions.  
The DC/AC converter is also connected to the DC bus to transfer the energy from the WSPS to the AC bus and then to the power grid, and convert the DC into AC. This part is called WCU and it is composed of the DC/AC converter connected to a wireless sensor network node, which is responsible for providing the required pulse-width modulation (PWM) signal to inject the energy generated by the PV modules into the grid. For that, the sensor node collects the required values of the inverter and then sends them to the coordinator node. In this case, the control strategy in the WCC is a PI that generates the control signal, which is provided to the inverter also by the sensor node. Moreover, a zero-crossing detector is required to synchronize the signal generated by the DC/AC converter with the grid. Thus, the inverter injects energy into the AC bus.  
Finally, the WCC consists of the wireless centralized network node, known as host or coordinator node. The host node is responsible for linking the wireless nodes of the DC/DC converter and the DC/AC converter by means of the IEEE 802.15.4 standard. In addition, the host also has to manage the communication in the sensor network and sends the generated control signals. Thus, the WCC contains the calculations of the control signal for the DC/DC converter to search for the MPP depending on the sensor measurements and the control strategy. The controller applied in this study is the adaptive Lyapunov control for the boost converter and the PI control for the inverter to obtain the control signals to inject the energy into the grid and to synchronize the voltages.