Identification and monitoring of a PEM electrolyser based on dynamical modelling

Abstract

Hydrogen from water electrolysis associated with renewable energies is one of the most attractive solutions for the green energy storage. To improve the efficiency and the safety of such stations, some technological studies are still under investigation both on methods and materials. As methods, control, monitoring and diagnosis algorithms are relevant tools. These methods are efficient when they use an accurate mathematical model representing the real behaviour of hydrogen production system. This work focuses on the dynamical modelling and the monitoring of Proton Exchange Membrane (PEM) electrolyser. Our contribution consists in three parts: to develop an analytical dynamical PEM electrolyser model dedicated to the control and the monitoring; to identify the model parameters and to propose adequate monitoring tools. The proposed model is deduced from physical laws and electrochemical equations and consists in a steady-state electric model coupled with a dynamical thermal model. The estimation of the model parameters is achieved using identification and data fitting techniques based on experimental measurements. Taking into account the information given by the proposed analytical model and the experimentation data (temperature T, voltage U and current I) given by a PEM electrolyser composed of seven cells, the model parameters are identified. After estimating the dynamical model, model based diagnosis approach is used in order to monitoring the PEM electrolyser and to ensure its safety. We illustrate how our algorithm can detect and isolate faults on actuators, on sensors or on electrolyser system. INTRODUCTIONIn recent decades, the global warming increases the average temperature of the air and oceans near the earth surface. This problem caused by CO 2 gas and several polluting wastes continuing to affect the lives in the world. In order to overcome this problem, the use of renewable energy and its optimization become a humanity challenge [3]. An attractive solution is to integrate efficient energy storages. The hydrogen is one of most promising vectors to store green energy. In the last years, numerous stations including renewable energy and electrolyser have been developed in order to optimise the electric energy production by increasing the storage capacity. The key idea is to convert the hydrogen into electricity using Fuel Cell (FC) when the renewable energy is off (no wind, no sun). In order to have this fuel, during the high potential periods, the extra renewable energy is converted using a Proton Exchange Membrane (PEM) electrolyser into H 2 . The global efficiency and safety of such installations (renewable energy source, fuel cell and electrolyser) lead to important research works in modelling, control [1] and monitoring. More precisely, it is necessary to propose an efficient supervision system. It permits to the user to decide if the hydrogen production station is faulty and if risk for itself and its environment could occur. For example, when sensor or actuator fault is detected, control l...

Dynamic operation and feasibility study of a self-sustainable hydrogen fueling station using renewable energy sources

“…The diffusion overpotential was characterized by equation (5), where b is the constant coefficient and i lim the diffusion limit current density [29]. The limiting current density is taken to be 1.55 A/cm 2 in our model, which is consistent with literature values [29]. The ohmic overpotential was due to the electrical resistances in the electrolyzer cell that are mainly due to proton conduction resistance in the proton exchange membrane.…”

“…The PEM electrolyzer cell voltage (V cell ) was expressed as equation (1), where E is the open circuit voltage, h act is the activation overpotential, h ohm is the ohmic overpotential and h diff is the diffusion overpotential [21,29]. Using the Nernst equation, the open circuit voltage was calculated by equation (2), where E 0 rev is the reversible cell voltage (1.23 V), R is the gas constant, T is the temperature of the electrolyzer; z is the number of moles of electrons transferred per mole of H 2 ; F is Faraday's constant; P H2 ,P O2 and P H2O are the partial pressures of hydrogen, oxygen, and water, respectively [20,30].…”

“…Using the Nernst equation, the open circuit voltage was calculated by equation (2), where E 0 rev is the reversible cell voltage (1.23 V), R is the gas constant, T is the temperature of the electrolyzer; z is the number of moles of electrons transferred per mole of H 2 ; F is Faraday's constant; P H2 ,P O2 and P H2O are the partial pressures of hydrogen, oxygen, and water, respectively [20,30]. The activation overpotential was based on electrochemical reaction kinetics and can be deduced from ButlereVolmer equation and rewritten for an electrolyzer as equation (3), where a is the transfer coefficient and i 0 is the exchange current density [29]. The diffusion overpotential was characterized by equation (5), where b is the constant coefficient and i lim the diffusion limit current density [29].…”

“…The activation overpotential was based on electrochemical reaction kinetics and can be deduced from ButlereVolmer equation and rewritten for an electrolyzer as equation (3), where a is the transfer coefficient and i 0 is the exchange current density [29]. The diffusion overpotential was characterized by equation (5), where b is the constant coefficient and i lim the diffusion limit current density [29]. The limiting current density is taken to be 1.55 A/cm 2 in our model, which is consistent with literature values [29].…”

“…The ohmic overpotential was due to the electrical resistances in the electrolyzer cell that are mainly due to proton conduction resistance in the proton exchange membrane. The ohmic overpotential was given by equation (5), where d m is the thickness of the membrane, A is the membrane crosssectional area, s m is the conductivity of the proton exchange membrane given by equation (6) proposed by Springer et al [31], where l E is the degree of humidification of the membrane, ranging from 14 (dry enough) to 22 (bathed) [20,21,29,30]. In the case of the PEM electrolyzer, the membrane can be considered to be fully hydrated and in this study, l E is assumed to be 17 representing good hydration.…”