IFAC PapersOnLine 52-29 (2019) 91–96 ScienceDirect ScienceDirect Available online at www.sciencedirect.com 2405-8963 © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Peer review under responsibility of International Federation of Automatic Control. 10.1016/j.ifacol.2019.12.627 © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. 1. INTRODUCTION The climate issues and oil depletion problem have paved opportunities to clean and sustainable energy sources as solar, wind and fuel cell electric source. Fuel cell energy systems is a promising solution for providing electric energy in stationary and automotive application and to guarantee climate friendliness and efficiency (Tolj et al, 2013 ). Besides, a fuel cell distributed energy systems is suitable for feeding isolated sites, in addition they generate power near the loads, which eliminates the need to run high-voltage transmission lines through rural and urban landscapes (Thounthong et al, 2011). Because of fuel cell low output voltage, a DC-DC converter is necessary to step up the DC bus voltage in order to match the load requirement (Benyahia et al, 2015). Thus, a conventional boost converter is mostly used. However, when a high output voltage is required by a load, a cascade boost converter is more suitable since it has a better voltage gain than the boost converter (Ndtoungou et al, 2012). Indeed, for a same output voltage the duty ratio of a conventional boost is higher than those of a cascade boost, this, relatively, increases thermal stresses in the boost switch (Ramos et al, 2008). This paper studies a nonlinear controller for a two stage cascade boost converter. It is shown that the transfer function from the duty ratio to the first inductor current, is a minimum phase transfer function (Ramos et al, 2008). Therefore, a current mode controller is designed using Lyapunov stability technique in order to regulate the output voltage. Moreover, the control law is based on a high gain observer estimating the unknown converter load current. Many researchers are studied the control of cascade boost converters, for instance, in (Ramos et al, 2008) a linear controller for a three-stage cascade converter around an The system under consideration, as depicted in fig. 1, is comprised of a fuel cell interfaced with a cascade boost converter (CBC) on the DC bus. An inverter is connected On the DC link to provide alternate current to feed houses or industrial loads. We suppose that, the fuel cell is involved in a distributed energy system and it is considered as the main source, it supplies loads when the demanded power has a slow dynamics. Otherwise, a storage device can assist the fuel cell when the loads require transient or fluctuating power. Typically, storage devises are connected on the DC link through back boost converter (BBC) and the sharing of the required power between sources is carried out by a power management system. In this paper we focuse on controlling the cascade boost converter. It is composed by two 2. SYSTEM OVERVIEW operating point has been proposed. Reference (Ndtoungou et al, 2012) presents a non linear control strategy for a two stages cascade boost converter. Likely, a sliding mode controller is used with two levels cascade boost in (Belhaj et al, 2017). In control field, Lyapunov stability tools are already used to design controllers for conventional boost converters (Tahri et al (2014 a, b), El Fadil et al, Tahri et al (2015 a, b)). To validate formal results, simulation is carried out in Matlab Simulink environment using Simpower System tools. All results show that the controller realizes the prescribed objectives. This study is organized as follows; in section II we present an overview of the studied system. In section III the cascade boost converter is modelled. Section IV is devoted to design an adaptive controller for the converter. In section V the control law is validated by numeric simulation. A conclusion and a reference list end the paper. Keywords: Fuel cell, boost converter, adaptive control, nonlinear observer, Lyapunov approach *ESIT Team, LGS Laboratory, ENSA, Ibn Tofail University, 14000, Kénitra, Morocco. (e-mails: abd.tahri@gmail.com; elfadilhassan@yahoo.fr; rachidaziz03@gmail.com) **Laboratoire d’Automatique de Caen, Université de Caen, Bd Marechal Juin, B.P 8156, 14032, Caen (e-mail: fouadgiri@yahoo.fr; eric.magarotto@unicaen.fr) Abstract: This study aims to design a controller for a cascade boost converter connected to a fuel cell in a distributed generator system. Knowing that the fuel cell voltage is too low to satisfy load requirement, and it varies with a nonlinear manner depending on the load current with uncertainties lying on fuel cell operating conditions, we use a DC converter to step up the low voltage and find out a control law to regulate the converter output voltage. Here, a lyapunov stability technique is used to design the nonlinear controller. An average current mode control method is adopted to satisfy the above objective. Moreover, a high gain observer is developed to estimate the converter output current instead of to be captured. Besides, the cascade boost converter is proved to be more suitable for high DC link voltage compared to a single boost converter. Theoretical studies and simulation using Matlab Simpower System tools show that the adaptive controller meets the objectives for what it is designed. Abdelouahad Tahri*, Hassan El Fadil*, Aziz Rachid*, Magarotto Eric**, Fouad Giri** A Nonlinear Controller Based on a High Gain Observer for a Cascade Boost Converter in a Fuel Cell Distributed Power Supply System