Nonlinear Adaptive Control for MPPT in Photovoltaic Systems H. El Fadil * , F. Giri GREYC Lab, Universite de Caen, Bd Marechal Juin, B.P 8156, 14032, Caen France (e-mails: elfadilhassan@yahoo.fr , giri@greyc.ensicaen.fr) * Corresponding author Abstract: We are considering the problem of maximum power point tracking (MPPT) in photovoltaic (PV) arrays. The PV power transferred to the battery through a controlled a PWM Boost power converter. As the maximum power point (MPP) of PV generators varies with solar radiation and temperature, an adaptive controller is proposed. The latter is designed using a backstepping technique, based on a nonlinear model describing the dynamics of the boost converter, the PV arrays and the battery. It is formally shown under mild assumptions that the developed adaptive controller actually meets the maximum power point tracking requirement. Keywords: Photovoltaic arrays, DC-DC converters, nonlinear adaptive control, backstepping control design. 1. INTRODUCTION The end of cheap petroleum price era and the increasing environmental preservation requirements make it more than ever necessary the development of clean and sustainable power generation sources. In this respect, photovoltaic power generators have gained a great popularity in recent years, due to their increasing efficiency and decreasing costs. Indeed, PV systems produce electric power without harming the environment, transforming a free inexhaustible source of energy, solar radiation, into electricity. Furthermore, PV devices are now guaranteed to last longer than ever and manufacturer warranties go over 20 years. Also, governments encourage resorting to such energy solutions through significant tax credits. All these considerations assure a promising role for PV generation systems in the near future. Dependence of the power generated by a PV array and its MPP on atmospheric conditions is readily be seen in the power-voltage (P-V) characteristics of PV arrays as shown in Fig 1 and Fig 2. These show in particular that the array power depends nonlinearly on the array terminal operating voltage. Moreover, the MPP, denoted ( m m P V , ), varies with changing radiation and temperature, necessitating continuous adjustment of the array terminal voltage if maximum power is to be transferred. Different techniques to maximise PV power transfer to various loads have been reported in the literature. Some of them consist in appropriately selecting the PV module characteristics to suit particular loads (Khouzam, ,1990; Applebaum, 1987). Others require changing the array configuration (switching the module parallel-series connections) in order to match the MPP to the load line (Braunstein and Zinger, 1981). However, theses techniques only approximate the maximum transfer of PV energy because they are associated with specific atmospheric and load conditions: when these conditions are changed, a loss of energy results. Another solution of PV maximisation, or MPPT, is based on continuous adjustment of the load seen by the PV array to coincide with its MPP (Hussein et al.,1995; Hiyama and Kitabayashi, 1997). In (Chiang et al., 1998) a residential PV energy storage system is presented, in which the PV power is controlled by a dc–dc converter of boost type. There, a current-mode control for the MPPT of the PV array is proposed, in which the converter is represented by its small-signal linear model. In (Eakburanawat and Boonyaroonate, 2006), the proposed solution involves a linear controller to ensure MPPT for a PV array together with a SEPIC dc-dc converter, supposing that temperature is the only varying parameter. In (Leyva et al., 2006) a stability analysis for MPPT scheme based on extremum-seeking control is developed for a photovoltaic (PV) array supplying a dc-to-dc switching converter. The analysis did not take into account the converter dynamics, i.e. the latter was only modelled by its steady state gain. More recently, (Fangrui et al., 2008) presented a modified variable step size incremental conductance algorithm that attempts to improve simultaneously the MPPT speed and accuracy. However, there too the converter dynamics were neglected in the algorithm development. In this paper, we propose a new solution to the problem of maximum power point tracking for a PV system involving PWM boost converter. Our solution consists in resorting to nonlinear adaptive control to cope with the varying