Centralized MPPT based on Sliding Mode Control and XBee 900 MHz for PV systems

Maximum Power Point Tracking (MPPT) algorithms are essential to achieve the best overall performance of PV systems. Typically, MPPT techniques are implemented over wired communications, which connect sensors, computing nodes and DC–DC converters. However, the introduction of wireless communication systems can offer more flexibility for information collection, dissemination, and processing when compared with wired communication infrastructures. This article proposes a wireless control architecture that allows the execution of the MPPT algorithms for several PV subsystems on a central node with limited computing power. This approach introduces flexibility and optimizes energy production at PV systems. The presented approach uses Current and Voltage measures, as well as the Irradiance and Cell Temperature values obtained at the PV panel, to calculate the optimal PWM duty cycle for the DC–DC converter which extracts the maximum power from the PV modules. Wireless communications are implemented by means of XBee 900 MHz RF modules. These modules provide a low cost solution with a relatively long range communication, avoiding the overpopulated 2.4 GHz band, in which other common technologies may cause interferences. Although the proposed approach allows the use of different control algorithms, Sliding Mode Control (SMC) techniques were selected, since this control technique ensures robustness and low computational complexity. The proposed SMC was simulated and compared with other conventional techniques with low computational cost, namely PID and P&O. Simulation results proved that SMC provides better performance and higher robustness when sudden changes in irradiance occur. The presented approach was experimentally tested in a PV rooftop installation at the Faculty of Engineering of Vitoria-Gasteiz. The obtained results suggest that it may be a valid way of maximizing energy production in PV systems while avoiding the constraints of wired communications.