Abstract
In this paper, the results of the sensitivity analysis applied to a fuel cell hybrid power system using a fuel economy strategy is analyzed in order to select the best values of the parameters involved in fuel consumption optimization. The fuel economy strategy uses the fuel and air flow rates to efficiently operate the proton-exchange membrane (PEM) fuel cell (FC) system based on the load-following control and the global extremum seeking (GES) algorithm. The load-following control will ensure the charge-sustained mode for the batteries’ stack, improving its lifetime. The optimization function’s optimum, which is defined to improve the fuel economy, will be tracked in real-time by two GES algorithms that will generate the references for the controller of the boost DC-DC converter and air regulator. The optimization function and performance indicators (such as FC net power, FC electrical efficiency, fuel efficiency, and fuel economy) have a multimodal behavior in dithers’ frequency. Furthermore, the optimum in the considered range of frequencies depends on the load level. So, the best value could be selected as the frequency where the optimum is obtained for the most load levels. Considering a dither frequency of 100 Hz selected as the best value, the sensitivity analysis of the fuel economy is further analyzed for different values of the weighting parameter keff, highlighting the multimodal feature in the parameters for the optimization function and fuel economy as well. A keff value around of 20 lpm/W seems to give the best fuel economy in the full range of load.
Highlights
Instead of a diesel generator [1], the proton-exchange membrane fuel cell (PEM FC) system could be used as a backup green energy source [2] for an FC hybrid power system (FC HPS) to mitigate the load variability by the load-following (LF) control [3,4,5]
The values obtained by simulation using the static feed-forward strategy [36], which is considered in this study as a reference strategy because it is the most known strategy implemented in commercial FC systems, are mentioned in the first column of these Tables
The sensitivity analysis of the dither’s frequency fd and weighting parameter keff was performed in this study in order to identify the best value of these parameters, which can be used to improve the fuel economy of an FC HPS
Summary
Instead of a diesel generator [1], the proton-exchange membrane fuel cell (PEM FC) system could be used as a backup green energy source [2] for an FC hybrid power system (FC HPS) to mitigate the load variability by the load-following (LF) control [3,4,5]. An active topology with two bidirectional DC-DC converters is more flexible as a control structure compared to a semi-active topology [9]. Energies 2019, 12, 2792; doi:10.3390/en12142792 www.mdpi.com/journal/energies (EMS), usually to regulate the DC voltage and mitigate the load pulses via the bidirectional DC-DC converters for the batteries and ultracapacitors stacks [5,7,11,12]. The control objectives for PEM FC system are as follows [15,16,17]: (1) minimization of the fuel consumption; (2) supplying the dynamic loads with energy, such as FC vehicles; (3) safe operation by using appropriate control loops to mitigate the load pulses, to limit the FC current slope, and to avoid fuel starvation
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