I. Quesada

Black-Box Model, Identification Technique and Frequency Analysis for PEM Fuel Cell With Overshooted Transient Response

Fuel cells are one of the most promising energy sources, especially for onboard applications. However, fuel cells present several drawbacks, such as slow dynamic response, load-dependent voltage, and unidirectional power flow, which cause an inappropriate vehicle operation. So, secondary energy sources and power converters must be implemented in order to satisfy fast changes in the current load and to store the energy delivered by the load if regenerative braking is intended. Taking into account the number and nature of the power converters, loads, secondary energy sources, and the possibilities for the control strategies, the design of a power distribution architecture based on fuel cells for transport applications is a complex task. In order to address these architectures, modeling and simulation design tools at system level are essential. This paper proposes a complete fuel cell black-box model which reproduces the behavior of a commercial fuel cell with overshooted transient response. The identification technique applied to parameterize the model components, based on manufacturers datasheets and a test based on load steps, is explained thoroughly. In addition, if only the fuel cell frequency response and manufacturers datasheet are available, an alternative parameterization methodology based on the fuel cell frequency response is presented. The fuel cell black-box model is validated experimentally using a commercial proton exchange membrane fuel cell. Two different parameterizations are carried out with the aim of verifying the robustness of both the fuel cell model and the proposed identification methodology.

Modulation Technique for Low Frequency Harmonic Cancellation in Auxiliary Railway Power Supplies

The auxiliary railway power supply (ARPS) is needed in order to provide low and medium voltages to the onboard systems from the catenary high voltage. The outputs of the ARPS can be dc (24 Vdc ÷100 Vdc) or ac (400 Vac). In the case of ac voltage generation, the ac output voltage is under very restrictive total harmonic distortion specifications even in the presence of nonlinear loads which draw low-frequency current harmonics. Along the present paper, a new modulation technique is proposed under the name of harmonic cancellation technique. It is based on the proper pre-distortion of the inverter output voltage in order to generate a controlled fundamental harmonic as well as a set of low-frequency harmonics which cancel out the harmonic pollution due to the nonlinear load performance. The theoretical background needed to implement the modulation technique is provided as well as the experimental validation of the proposed modulation technique through a scale-down prototype.

Black-box model and identification methodology for PEM fuel cell with overshooted transient response

One of the power sources with most potential is fuel cells, especially in on-board applications. The design of a power distribution architecture based on fuel cells for transport applications is a complex task, due to the number and nature of the power converters, loads, secondary energy sources, etc. Modeling and simulation are essential design tools at system level. This paper proposes a complete fuel cell black box model, in order to reproduce the behavior of a commercial fuel cell with overshooted transient response. The model is parameterized by applying an identification methodology based on manufacturers datasheets and a test based on load steps. The fuel cell black-box model is validated experimentally using a commercial PEM (Proton Exchange Membrane) fuel cell.

Optimal sizing of propulsion systems applied to fuel cell based vehicles

The propulsion system implemented in a fuel cell based vehicle strongly affects the mass, cost and volume of the overall system. The design of a propulsion system architecture, which comprises different power converters and secondary energy storage systems, is closely related to the driving profile applied, since the power and energy requirements depend on the driving profile. This paper tackles the optimum sizing of the secondary energy storage systems, as well as the set of equations that describes the mass and cost of each one of the power train subsystems. After that, ten different propulsion systems are analyzed in order to determine which of them minimize the mass, cost and volume depending on the power delivered by the fuel cell.

Improved modulator for THD reduction in onboard generation of three phase AC voltage

AC voltage generation in rail applications (auxiliary services), usually employs optimized PWM feedforward schemes in order to control the inverter. In this kind of applications the THD reduction of the filtered output voltage together with the reduced weight of the static converters are the main goals to be reached. In order to achieve these objectives, the most commonly used optimized PWM techniques are going to be compared in terms of Total Harmonic Distortion (THD), Weighted Total Harmonic Distortion (WTHD) and IGBT losses.

PWM-VSI overmodulation technique with carrier harmonics reduction for auxiliary railway power supply

Auxiliary railway power supplies are needed onboard rolling stock to provide medium or low voltage to different systems from the catenary. In this kind of applications, the THD reduction of the filtered output voltage and a great regulation capability associated to the wide input catenary voltage range are the main goals to be reached. In order to achieve these objectives a novel overmodulation strategy for voltage-source inverters is presented. The new overmodulation technique has been tested and validated trough an auxiliary railway power supply prototype. Experimental results demonstrate the feasibility and the effectiveness of the proposed technique.

Novel Simplified Controller for Three Phase Grid Connected Inverter Based on Instantaneous Complex Power

This paper presents the control of three-phase inverters connected to the grid by using the concepts of the Instantaneous abc Theory and the effective apparent power Se. These concepts allow the control of the three-phase inverter from a phasorial point of view both in magnitude and phase. The regulation of the instantaneous reactive power Q allows the instantaneous control of the phase delay ¿ between the grid voltage and the first harmonic of the voltage generated by the three-phase inverter. The calculation of Se allows the instantaneous control of the modulation index m, proportional to the magnitude the inverter voltage. By using these two concepts, it is easy to implement a control of the power flowing to the grid, with variables controlled in DC by means of PI regulators and by using simple calculations. The proposed control is compared with the Stationary and Synchronous Reference Frame Techniques considering the computing cycles. Simulation results are included to illustrate the effectiveness the proposed control.

Control strategy improvement for a parallel power distribution architecture based on fuel cells and supercapacitors

The use of fuel cells as main source of energy is suffering an important increase, due to their continuous improvements and their good performances. Fuel cells are being used in very different industrial applications, and they are being particularly applied in automotive field. So, there is an important growing in the study of new power distribution architectures based on fuel cells.

Practicing design method of regulators for cascaded converters

Current trends in power distribution systems are focused on distributed architectures instead of centralized approach. Distributed architectures are more complex since a network of power electronic converters is required to distribute power with appropriate performance. Moreover, they are typically comprised of subsystems made up by a variety of manufacturers, which do not provide the data required to parameterize a model due to reasons of confidentiality. In this paper, a method to design power converter regulators for cascaded converters is proposed. The aim is to provide a practicing design criterion of the regulator that avoids complex power system measurements.

Improved modulator for losses reduction in auxiliary railway power supplies

This paper presents the losses optimization through an optimal modulation strategy for auxiliary railway power supplies. The figures of merit analyzed to compare different modulation techniques are the transformer losses and the inverter losses. For the transformer losses a model has been developed for the special characteristics of this element due to its integrated magnetism. In the case of the switching devices, the losses have been obtained by means of a simulator. Both, the transformer and the switching device losses have been experimentally validated in a scale-down prototype, so the analysis can be extrapolated to other power converters.