Comparison of Fuel Consumption and Fuel Cell Degradation Using an Optimised Controller

Abstract

The Energy Management Strategy (EMS) of any hybrid vehicle is responsible for determining the operating state of many components on board the vehicle and therefore has significant effect on the fuel economy, emissions, ageing of components and vehicle drive-ability. It is generally accepted that Stochastic Dynamic Programming (SDP) can be used to produce a near-optimal control strategy provided that an accurate Markov model of the drive-cycle is available, and the cost function used for the optimisation is representative of the true running cost of the vehicle. The vast majority of research in this field focussing solely on the optimisation of the fuel economy, however for a fuel cell hybrid vehicle, the degradation of the fuel cell contributes significantly to the overall running cost of the vehicle, and should therefore be included in calculation of the running cost during the optimisation process. In this work, an optimised controller using SDP is developed for a campus passenger vehicle in order to minimise the lifetime cost of both fuel consumption and fuel cell degradation. The vehicle is then simulated over a number of typical journeys obtained from data logging during its use on the University of Birmingham's campus. It is shown that the expected lifetime cost due to fuel cell degradation massively outweighs the cost of the fuel consumed.

Optimal Cost Minimization Strategy for Fuel Cell Hybrid Electric Vehicles Based on Decision-Making Framework

“…But the fuel cell degradation is not considered into the optimal objectives of these studies. In [10], minimizing the hydrogen and fuel cell lifetime costs as the objective function is solved through stochastic dynamic programming (SDP). Three representative EMSs: DP, PMP, and MPC in [11] are developed to minimize hydrogen consumption and fuel cell durability.…”

Cost-Optimal Energy Management of Hybrid Electric Vehicles Using Fuel Cell/Battery Health-Aware Predictive Control

“…Fuel cell lifetime was governed by imposing constraints on fuel cell output power in ECMS [30], PMP [31], and CP [14] energy management controllers. A stochastic DP controller to minimize the summation of hydrogen and fuel cell costs was introduced in [32], [33] as well. However, these studies did not take energy storage degradation into consideration.…”

“…Since vehicular applications are invariably subject to drastically dynamic loading, it is of particular significance and practicality to carefully govern the PEMFCS loading (i.e., output power) to alleviate its performance degradation and increase the overall vehicular economy. It has been demonstrated in [32], [33], [40] that on/off loading has a predominately negative impact on the lifetime of PEMFCS, especially in heavy-duty vehicular applications. Therefore, as manipulated in [14], [22], [34], the bus PEMFCS is herein always on.…”

The Effect of Fuel Cell and Battery Size on Efficiency and Cell Lifetime for an L7e Fuel Cell Hybrid Vehicle

“…It has been found [13,14] that the 1.2 kW fuel cell is underpowered for its application, but a 4.8 kW fuel cell would likely be overpowered for campus usage [15]. This suggests that the optimal size of fuel cell is likely somewhere between these values, and therefore it has been decided to explore fuel cells with a maximum power of between 1.2 kW and 4.8 kW.…”

“…This was below expectations, and significantly below that of other fuel cell vehicle concepts at the time. It was determined that significant gains could be made by optimisation of the control strategy and a system level re-design of the sizing of various powertrain components; in particular, the 1.2 kW fuel cell which was too small to maintain the battery State of Charge (SoC) over the typical usage cycles [14]. Previous work by the authors [15] has shown that an up-sized 4.8 kW fuel cell eliminates this problem and also, by using optimal Stochastic Dynamic Programming (SDP) control, the fuel economy could be improved by around 27% when compared to the original vehicle.…”