Abstract
Impedance measurements by EIS are used to build a physical circuit-based model that enables various fault diagnostics and lifetime predictions. These research areas are becoming increasingly crucial for the safety and preventive maintenance of fuel cell power systems. It is challenging to apply the impedance measurement up to commercial applications at the field level. Although EIS technology has been widely used to measure and analyze the characteristics of fuel cells, EIS is applicable mainly at the single-cell level. In the case of stacks constituting a power generation system in the field, it is difficult to apply EIS due to various limitations in the high-power condition with uncontrollable loads. In this paper, we present a technology that can measure EIS on-line by injecting the perturbation current to fuel cell systems operating in the field. The proposed EIS method is developed based on Simulink Real-Time so that it can be applied to embedded devices. Modeling and simulation of the proposed method are presented, and the procedures from the simulation in virtual space to the real-time application to physical systems are described in detail. Finally, actual usefulness is shown through experiments using two physical systems, an impedance hardware simulator and a fuel cell stack with practical considerations.
Highlights
Fuel cells have been researched to use widely in stationary power plants, transportation, and buildings
Since the root mean square error (RMSE) between Figure 5a,b is 7.53 × 10−4, the proposed method can accurately measure the impedance of the fuel cell regardless of the value of load connected to the fuel cell stack
Since the root mean square error (RMSE) between the ideal case and the experiment with the hardware simulator over the trajectory is 0.165, the electrochemical impedance spectroscopy (EIS) method can track the entire trajectory of the Nyquist plot without a significant error so that it can be used for the diagnosis of fuel cell stacks, where it is important to detect the feature indicator through the change of patterns of impedance characteristics [17,18]
Summary
Fuel cells have been researched to use widely in stationary power plants, transportation, and buildings. EIS experiments require expensive frequency response analyzer (FRA) equipment for signal perturbation as well as potentiometers or galvanometers for building a manageable load [21] This equipment has a limitation that only low power capacity is available for the measurements, which cannot handle the power and voltage level of commercial power systems. Laboratory-oriented EIS is sufficient to apply for investigating the electrochemical properties of materials at the single-cell level This method has many limitations to use the EIS as a tool for diagnosis or prognostics for fuel cell stacks in an actual field because it needs to handle high power and energy with uncontrollable loads. To show the effectiveness of the proposed EIS, the Nyquist plot from the impedance calculated through simulation is compared with one obtained by the mathematical calculation based on the following impedance equation
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