# Online Model Adaption for Energy Management in Fuel Cell Electric Vehicles (FCEVs)
## 1 Introduction  
The transport sector represents almost a quarter of Europe's greenhouse gas emissions and is the main cause of air pollution in cities. Facing this problem, the European Commission (EU) established a series of legislative proposals to decrease the total emissions of the transport fleet, with the final purpose of achieving climate neutrality in the EU by 2050. To carry out this transition, the EU defined an intermediate target of an at least 55% net reduction in greenhouse gas emissions by 2030 [1]. Considering that petroleum-based fuels used in internal combustion engines (ICEs), which are extensively used in vehicle propulsion, are a key actor in the problem of greenhouse gases and air pollution [2], several technologies to progressively replace them are currently on the market. One possibility is the use of hydrogen-based and carbon-neutral fuels [3] to retain the technological knowledge and productive infrastructure of almost a century of ICE development. Another option is the use of battery electric vehicles (BEVs) and hybrid electric vehicles (HEVs). Different types of HEV architectures are designed to accommodate diverse driving needs, efficiency requirements, and technological advancements, and this subject has been widely discussed in the literature [4; 5]. A fuel cell electric vehicle (FCEV) is essentially an electric vehicle that combines batteries with a fuel cell to power its onboard electric motor [6]. The fuel cell converts chemical into electrical energy without going throughother energy forms such as thermal and mechanical. Therefore, the efficiency of the fuel cell is not limited by Carnot's cycle, and an FCEV can reach triple the fuel efficiency of a regular gasoline-powered car in some operating conditions [7]. However, fuel cells (FCs) have some drawbacks, such as limited range due to difficulties with hydrogen storage onboard, lack of a hydrogen recharging infrastructure, and safety challenges [8]. So these limitations and system complexity add cost to the production and use of this technology. On the other hand, the source of hydrogen production is an important factor that needs to be considered when defining hydrogen as clean energy. In this sense, when hydrogen is produced by electrolysis using photovoltaic, wind power, or hydraulic power as the source of energy, it is known as green hydrogen [9]. Nevertheless, 95% of the total current worldwide hydrogen production comes from fossil sources and just 4% from electricity [10]. Given the complexity of FCEV powertrains, specifically due to the multiple energy storage systems, the energy management strategy (EMS) is essential for their efficiency and energy consumption [11]. For each situation, the EMS decides the percentage of the vehicle power demand that must be supplied by each of the energy sources [12]. Also, to make this propulsion system competitive and economically viable compared to traditional KCE, there are still many challenges, such as high maintenance costs and short lifecycle [13]. These challenges are related to the interaction between several ageing mechanisms that react differently with various operating conditions that cause a drop in system performance. The ageing process in fuel cell components also affects the operation of the EMS; however, this aspect is barely considered in the FCEV EMS [14]. Due to the simplicity required for real-time applications, models used for powertrain control are susceptible to uncertainties due to several factors, such as modelling simplifications, limitations in the range of situations considered during calibration, dynamic changes, measurement errors, unit-to-unit variability, or ageing. These errors are propagated to the powertrain control, ultimately impacting the overall performance of the vehicle. In vehicle control applications, electronic control units (ECUs), crucial components in commercial vehicle applications, manage various functions such as engine management, transmission control, and braking systems.