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In many grid-connected applications a dc/dc switching converter is usually connected between the PV modules and the inverter. This paper presents an improved procedure to design a sliding controller for the PV system, which drives the PV voltage to follow a reference provided by an external MPPT algorithm and mitigates the perturbations caused by the irradiance changes and oscillations in the bulk-voltage. By considering that the switching surface is the linear combination of the input capacitor current and the PV voltage error, the proposed design exhibits advantages in comparison with existing solutions that rely in the linearization of inner current loop dynamics. The proposed integral procedure, by taking also into account the effects in the closed loop system dynamics of a reference filter, ensures a stable sliding regime in all the desired operation range of the system, while the settling time and overshoot of the PV voltage required by an MPPT algorithm are provided. Differently from a previous similar but less rigorous approach, the switching function and reference filter parameters are obtained by numerically solving a set of nonlinear equations. Simulations and experiments were used to demonstrate the efficiency of the proposed solution in presence of environmental and load perturbations. 0885-8993 (c)

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This paper presents the parameter identification of an equivalent circuit-based proton exchange membrane fuel cell model. The model is represented by two electrical circuits, of which one reproduces the fuel cell's output voltage characteristic and the other one its thermal characteristic. The output voltage model includes activation, concentration, and ohmic losses, which describe the static properties, while the double layer charging effect, delays in fuel and oxygen supply, and other effects provide the model's dynamic properties. In addition, a novel thermal model of the studied Ballard's 1.2 kW Nexa fuel cell is proposed. The latter includes the thermal effects of the stack's fan which significantly improve the model's accuracy. The parameters of both, the electrical and thermal, equivalent circuits were estimated on the basis of experimental data by using an evolution strategy. The resulting parameters were validated by the measurement data obtained from the Nexa module. The comparison indicates a good agreement between the simulation and the experiment. In addition to simulations, the identified model is also suitable for usage in real-time fuel cell emulators. The emulator presented in this paper additionally proves the accuracy of the obtained model and the effectiveness of using an evolution strategy for identification of the fuel cell's parameters.

This paper presents, in a tutorial manner, nonlinear phenomena such as bifurcations and chaotic behavior in DC-DC switching converters. Our purpose is to present the different modeling approaches, the main results found in the last years and some possible practical applications. A comparison of the different models is given and their accuracy in predicting nonlinear behavior is discussed. A general Poincaré map is considered to model any multiple configuration of DC-DC switching converters and its Jacobian matrix is derived for stability analysis. More emphasis is done in the discrete-time approach as it gives more accurate prediction of bifurcations. The results are reproduced for different examples of DC-DC switching converters studied in the literature. Some methods of controlling bifurcations are applied to stabilize Unstable Periodic Orbits (UPOs) embedded in the dynamics of the system. Statistical analysis of these systems working in the chaotic regime is discussed. An extensive list of references is included.

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