978-1-4577-1510-5/11/$26.00 ©2011 IEEE An Intelligent Control of Solid oxide Fuel cell voltage Kanhu Charan Bhuyan and Kamalakanta Mahapatra Dept of ECE, National Institute of Technology-Rourkela, India-769008 Email: kanhu2006@gmail.com, kmaha2@rediffmail.com Abstract— This paper presents a comprehensive non-linear dynamic model of a solid oxide fuel cell (SOFC) that can be used for transient behaviors studies. The model based on electrochemical and thermal equations, accounts for temperature dynamics and output voltage losses. The relaxation time is strongly related to the transient temperature distribution of the solid oxide fuel cell structure. Therefore, it is in the order of some minutes depending on the design parameters and the operating conditions. The model contains the hydrogen, oxygen and water block separately. Other blocks are concentration, activation and ohmic losses block. The analytical details of how active and reactive power output of a stand-alone solid oxide fuel cell power plant (FCPP) is controlled. This analysis depends on an integrated dynamic model of the entire power plant including the reformer. Keywords— Fuel cell, FCPP, SOFC and Reformer. I.INTRODUCTION Many researchers reported on of Molten carbonate fuel cell. Looking back, in 2004, Francisco Jurada presented a model of ‘Solid oxide fuel cell’ without considering the temperature effect. The concept of molten carbonate fuel cell is exactly similar to solid oxide fuel cell. This comparison is given in [1] and [2]. The fuel input to the fuel cell is changing in steps in a paper in the literature[3]. Another very useful model is available in the literature which was suggested by Kourosh Sedghisigarchi, [3] and [4] .This paper considers all the subsystems of fuel cell, that includes hydrogen block, oxygen block, water block, activation and concentration block, and temperature block. In temperature block, the relaxation time is closely related to the transient temperature distribution of the solid oxide fuel cell structure. The internal cell resistances are strongly temperature dependent. Thus, the relaxation time depends on the thermal properties, size and configuration of the cell, and operating conditions. In [5] and [3], SOFC model is given without considering thermal unit. However, in this paper, these structures are modified by the modeling thermal unit. A first comprehensive nonlinear dynamic model of solid oxide fuel cell that can be used for dynamic and transient stability studies is developed by K. Sedghisigarchi, Ali Feliachi in 2004 [6]. The model based on electrochemical and thermal equations, accounts for temperature dynamics and voltage losses. The output voltage response of a stand-alone fuel-cell plant to a step change, a fuel flow step change, and fast load variations are simulated to illustrate the dynamic behavior of SOFC for fast and slow perturbations. This paper presents a SOFC model and designs the control strategies for the AC voltage control and the active/reactive power control of the DC/AC inverter. Two separate controllers are designed for these purposes. The fuzzy logic control scheme is employed for the design of the two controllers. II.PRINCIPLES OF FUEL CELL MODEL The fuel cell (FC) is an electrochemical device that converts chemical energy of hydrogen gas ( 2 H ) and oxygen gas ( 2 O ) into electrical energy. The solid oxide fuel cell consists of two porous ceramic electrodes separated by a dense ceramic electrolyte. The cell produces electricity by the electrochemical reaction of fuel (hydrogen and / or carbon monoxide) and the oxidant (oxygen) across the solid electrolyte. Oxygen fed to the air electrode (cathode) accepts electrons from the external circuit to form oxygen ions. The ions are conducted through the solid electrolyte to the fuel electrode (anode). At the fuel electrode, the ions combine with hydrogen and/ or carbon monoxide in the fuel to form water and /or carbon monoxide. This reaction releases electrons. Electrons flow from the fuel electrode (anode) through the external circuit back to the air electrode (cathode).The overall reaction is exothermic; the cell produces heat in addition to electricity. A typical fuel cell reaction is given below. The chemical reactions inside the cell that are directly involved in the production of electricity are given as At Anode: - - - - - - - + → + + → + e CO O CO e O H O H 2 2 2 2 2 At Cathode: - - - → + 2 2 2 4 O e O Overall: 2 2 2 2 CO O H CO O H + → + + Fig. 1 Basic operation of Fuel Cell