Now showing 1 - 4 of 4
  • Publication
    Metadata only
    Modeling and experimental parameterization of an electrically controllable PEM fuel cell
    Optimized integration of fuel cells into grids or on-board power supplies is necessary to facilitate replacement of conventional energy producers by a reliable and plannable power generation technology. Due to the interdependency between fuel cell current and voltage, integration of fuel cells requires a power conditioning system, which increases integration weight and cost. For this reason, integration of electric field modifier electrodes into the setup of proton exchange membrane fuel cells is a new approach to control the output voltage in order to minimize the subsequent power conditioning system. This approach considers the physics of proton transport through the electrolyte membrane and could offer a lever to control the ohmic resistance. In this paper, a fuel cell model is implemented in MATLAB and extended by electric field modifier electrodes, allowing control of the ohmic resistance through an externally applied voltage. The concept of boosting and attenuating fuel cell voltage is presented along with different setups to enable this behavior. Furthermore, an electrical equivalent circuit for electrically controllable fuel cells is developed and implemented in MATLAB/Simulink. A method to parameterize the developed MATLAB and Simulink models by first experimental results is presented.
  • Publication
    Metadata only
    Short-circuit behavior of a PEM fuel cell stack under various operating conditions
    Optimized grid integration of proton exchange membrane fuel cells in various possible applications requires a suitable protection system. For this reason, this paper examines the transient behavior of a fuel cell stack after an external electrical shortening. In order to show the influence of operating parameters on the short-circuit behavior, various experiments with changed anode and cathode humidity, cell temperature and anode and cathode stoichiometry are carried out. With this, manufacturers can estimate the short-circuit magnitude of their stacks and recommend a suitable plant protection system. It could be shown that the peak short-circuit current depends on the operating point as well as the operating conditions. For the steady-state short-circuit current, the gas stoichiometry has an impact on the deliverable current. For all other operating conditions the steady-state short-circuit current is approximately twice the recommended maximum operating current. Furthermore, a method to estimate the effective fuel cell stack capacity out of the transient short-circuit current is presented.
  • Publication
    Metadata only
    Short Circuit Characteristics of PEM Fuel Cells for Grid Integration Applications
    The reduction of greenhouse gas and pollutant emissions is a major issue in modern society. Therefore, environmentally friendly technologies like fuel cells should replace conventional energy generation plants. Today, fuel cells are used in households for CHP (combined heat and power) applications, for emergency power supply in many stationary applications and for the power supply of cars, buses and ships and emergency power supply of aircrafts. A significant challenge is the optimal electrical grid integration and selection of the appropriate grid protection mechanism for fuel cell applications. For this, the short circuit capability and behavior needs to be known. This paper gives a mathematical estimation of the short circuit behavior of fuel cells. Five main transient and dynamic phenomena are investigated. The impact of the main transient effect for the provision of additional short circuit energy is simulated, and the simulation is experimentally validated. For this purpose, a 25 cm2 single cell consisting of a NafionTM 212 membrane and carbon cloth electrodes with a catalyst loading of 0.5 mg/cm2 Pt is analyzed. The magnitude of the transient short circuit current depends on the operating point right before the short circuit occurs, whereas the stationary short circuit current of fuel cells is invariably about twice the operational current. Based on these results, a novel fuel cell model for the estimation of the short circuit behavior is proposed.