Fuel cell hardware-in-loop
Introduction
Fuel cell system and fuel cell vehicle (FCV) simulation are standard techniques in the FCV and system design development process. Today the application of simulation techniques primarily supports the analysis of different concept system configurations (hybrid versus load following, component size and arrangement, etc.). FCV simulation assists in the early vehicle development phase as part of the process of seeking an optimal concept configuration that meets the minimum or desired application requirements. In practice, the minimum requirements of the proposed vehicle configuration (range, fuel efficiency, acceleration, top speed, pay load, etc.) are defined, set as targets, and the concept configurations are evaluated by the method of numerical simulation.
For concept development at the beginning of the FCV development process, a number of different simulation tools are available today and have been benchmarked [1]. It was found that, in general, the available tools could be separated into two general groups, one group of tools with a non-causal approach and a second group of tools based on a causal approach. While the “non-causal” tools require less computational resources, the inherent non-causality in this group of models cannot support applications in the rapidly expanding field of system evaluation and validation through hardware-in-Loop (HiL) and rapid prototyping (RP) methodologies. In contrast, although the causal tools require significantly higher computational resources they are required for detailed dynamic FCV simulation (at the subsystem and component level), and are absolutely necessary for the development of HiL methodologies.
This paper describes the adaptation of a dynamic FCV simulation tool for application to fuel cell HiL for dynamic system applications, reviews the development of the initial experimental HiL tool, and applies this tool to an example fuel cell system and vehicle application. This is the first step toward establishing a general fuel cell HiL methodology.
The Hawaii Natural Energy Institute (HNEI) of the University of Hawaii has designed and installed a dynamic fuel cell test system with the goal of demonstrating the concept of fuel cell HiL as a general tool for the development and evaluation of fuel cell components and system designs in highly dynamic applications—e.g., automotive traction power within a FCV. The fuel cell test system dynamic response (pressure, flow, humidification, etc.) required for the FCV application is ∼1 s, ca. 3 orders of magnitude faster than the values typically used for static fuel cell testing (e.g., 10–20 min per V–I pair).
The initial hardware-in-loop implementation (HiL #1) was commissioned at HNEI in January–February 2006 and is currently in operation at the Hawaii Fuel Cell Test Facility. HiL#1 is being tested and modified to establish the capability for evaluation of the transient response of fuel cells in dynamic applications.
This paper describes the key elements of the HNEI hardware-in-loop concept, the structure and methodology underlying the step from simulation to HiL, and illustrates, by example, the extension of a FCV simulation tool into an experimental HiL tool.
Experimental results are presented to demonstrate the capabilities of this new fuel cell HiL technique for FCV applications. This demonstration uses the simulation of a hydrogen FCV, standard international driving cycles, and a fuel cell as the HiL component.
Section snippets
Simulation methodology
This section outlines the methodology of a dynamic simulation tool for fuel cell passenger vehicles, FCVSim, and illustrates how it is adapted for the HiL methodology. The details underlying the FCVSim simulation tool have been presented in detail in literature [2], [3], [4], [5], and will only be briefly reviewed here at a level sufficient to understand the HiL adaptation of this tool—the subject of this paper.
Fig. 1 shows the highest level structure of the FCVSim simulation tool, for a fuel
Adaptation of the FCVSim tool for HiL applications
As an example of the adaptation of the FCVSim tool for a HiL application the simplest FCV system (i.e., a direct-hydrogen load-following FCV design) is used.
A controls engineering view of the direct-hydrogen fuel cell system is provided in the literature [2], and a detailed exposition on the fuel cell system simulation for the direct-hydrogen FCV is also available [6]. Fig. 2 illustrates the physical configuration of the direct-hydrogen fuel cell system within the load-following version of
Applied software chain
For choosing the software tools applied in this project, several criteria were considered as important. These key criteria for the basic software tools are:
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commercially available (no in-house solutions);
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must be an industry standard, as closely as possible;
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have high flexibility;
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transparency and ease of use;
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seamless integration of HiL and RP features;
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scalability (easy entry with the possibility to move ahead to highly specialized development projects).
Initial experimental HiL results
Implementation of the initial fuel cell hardware-in-loop system (designated as HiL#1) is illustrated in Fig. 5.
This software plus hardware combination has as an objective the evaluation of the performance of a fuel cell test object under conditions that would exist in a fuel cell system within an FCV being driven over a test drive cycle. That is, to expose the fuel cell to the dynamic operating conditions (current demand, fuel and air flows, etc.) that it would experience in a fuel cell system
Summary
The experimental implementation of an initial fuel cell HiL capability has been undertaken at the Hawaii Fuel Cell Test Facility of the Hawaii Natural Energy Institute at the University of Hawaii. This paper presents an overview of the fuel cell HiL concept and the design and experimental configuration of this dynamic fuel cell test system, which is designated as HiL #1. The implementation of HiL #1 has been discussed in terms of the basic fuel cell HiL methodology, the experimental
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