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In this paper, a polymer-electrolyte-membrane fuel-cell (FC) model that is useful for simulation and control purposes is presented. The model uses both electrical-circuit components and functional blocks to reproduce both static and dynamic FC behaviors. Its main feature is in the reproduction of the oxygen-excess-ratio behavior, but it is also able to interact with any electrical device connected at the FC terminals, e.g., a load or a switching converter. Consequently, the proposed model can be used to develop new control strategies aimed at avoiding the oxygen-starvation effect and/or minimizing the fuel consumption. The model has been customized for a Ballard Nexa 1.2-kW power system, and this has allowed an experimental validation by means of measurements performed on a real FC device. [ABSTRACT FROM AUTHOR]

Subharmonic oscillation is widely studied in switching converters under current mode control (CMC). Its boundary of occurrence in the design parameter space is well known in the case of an infinite-bandwidth current sensor. However, in a practical implementation, either a limited-bandwidth current sensor or an additional filter is used. This could have an effect on the system dynamics particularly for relatively high switching frequencies. This paper discusses the effect of the additional dynamics due to the finite-bandwidth current sensor or the additional filter on the stability and subharmonic oscillation boundaries in switching converters under CMC. It is shown that a simplified model, taking into account the dynamics of the inductor current and the sensor/filter, is enough to obtain accurate results concerning the prediction of the occurrence of subharmonic instabilities in switched converters. Design-oriented equations describing the occurrence of subharmonic oscillations are used to show some problems related to the additional dynamics on the ramp compensator design in a single-switch dc–dc converter working in continuous conduction mode. Some proposed solutions are also discussed. Numerical simulations and experimental measurements corroborate the theoretical predictions. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel maximum power point tracking (MPPT) technique aimed at maximizing the power produced by photovoltaic (PV) systems. The largest part of the MPPT approaches presented in the literature are based on the sensing of the PV generator voltage. On the contrary, in this paper, a current-based technique is proposed: the sensing of the current in the capacitor placed in parallel with the PV source is one of the innovative aspects of the proposal. A dual control technique based on an inner current loop plus an outer voltage loop allows to take profit of the fast current tracking capability of the inner current loop while the voltage loop benefits from the logarithmic dependency of the PV voltage on the irradiation level. The features of the proposed algorithm, particularly in terms of tracking of irradiation variations and disturbance rejection, are supported by theoretical analysis, simulations, and experimental results. The technique described in this paper is patent pending. [ABSTRACT FROM PUBLISHER]

This paper deepens in the study of the recently described diffusive proton exchange membrane fuel cell (FC) model. This model has demonstrated a close agreement to the experimental data provided by a real FC. The diffusive model is approximated by a finite-dimensional model that allows formulating an optimization problem of least square error type to estimate the model distribution. The diffusive model is identified by means of experimental measurements of current (input) and voltage (output) in the FC. It is well known that the FC static current–voltage characteristic has three operation regions, with only the ohmic region being strictly linear, so that it is very difficult to approximate the whole operation range with a linear model. Therefore, a new method is presented in this paper extending the diffusive approach by means of a linear parameter-varying model with the aim to overcome the limitations of linear time-invariant models. In addition, discrete-time expressions for the new diffusive model approach are derived. The obtained model is simple and can be used in systems that require real-time emulators or complex long-time simulations. Experimental results using the Ballard Nexa 1.2-kW FC illustrate the advantages of the new diffusive model approach with respect to previous reports. [ABSTRACT FROM PUBLISHER]

In this paper, a serial–parallel hybrid (SPH) power system formed by a fuel cell (FC), an auxiliary storage device (ASD), and the current-controlled dc–dc converters responsible for the power management are realized by using the digital signal controller (DSC) TMS32F28335. The main energy management goal is to transfer energy from the sources (FC or ASD) to the load while ensuring dc bus voltage regulation and high power conversion efficiency. In addition, a safe and reliable operation of the system has to be achieved. The selected converter and its controller features are noninverting voltage step up and step down, high efficiency, regulation of input and output currents and low ripple values, and the ability to change from input to output current regulation loop, suddenly and smoothly, and vice versa. All these features allow it to be positioned in different FC system localizations and simplify the design of the master control. Simulation and experimental results have been validated on a 48-V 1200-W dc bus. [ABSTRACT FROM PUBLISHER]

The oxygen starvation phenomenon is a dangerous operating condition that reduces the lifetime of PEM fuel cells. The detection and prevention of this undesired phenomenon require estimation of the oxygen excess ratio \lambdaO2. The mathematical complexities of the reported methods for obtaining \lambdaO2 complicate its real-time calculation and require high-performance computational devices, which significantly increase the costs of the system. In this paper, a mutual information approach is used in obtaining a simplified mathematical model for the calculation of \lambdaO2. The usage of such a simplified model requires much less computational power for real-time monitoring of the variable \lambdaO2, while it provides comparable results to those obtained by using the complex model. Therefore, it represents a cost-effective solution, suitable for usage within applications that require high sampling frequencies, like emulators, converter and air compressor control loops, simulations, etc. In order to validate the accuracy of this simplified \lambdaO2 calculation model, a real-time monitoring system was built and experimentally tested using both the simplified and complex models. The matching experimental results validate the proposed simplification and justify the use of this simplified model within real-time monitoring applications. [ABSTRACT FROM AUTHOR]