###### Abstract  
The utilization of fuel cells (FC) in automotive technology has experienced significant growth in recent years. Fuel cell hybrid electric vehicles (FCHEVs) are powered by a combination of fuel cells, batteries, and/or ultracapacitors (UCs). By integrating power converters with these power sources, the FCHEV system can overcome the limitations of using them separately. The performance of an FCHEV is influenced by the efficiency of the power electronics converter controller, as well as the technical efficiency of the power sources. FCHEVs need intricate energy management systems (EMSs) to function effectively. Poor EMS can lead to low efficiency and accelerated fuel cell and battery degradation. The literature discusses various types of EMSs such as equivalent consumption minimization strategy, classical PI controller, fuzzy logic controller, and mutative fuzzy logic controller (MFLC). It also discusses a systematic categorization of FCHEV topologies and delves into the unique characteristics of these topologies. Furthermore, it provides an in-depth comparative study of EMSs applied in FCHEVs, encompassing rule-based, optimization-based, and advanced learning-based approaches. However, comparing different EMSs can be challenging due to the varying vehicle and system parameters, which might lead to false claims being made regarding system performance. This review aims to categorize and discuss the various topologies of FCHEVs, highlighting their pros and cons, and comparing several EMSs based on performance metrics such as state of charge (SOC) and FC deterioration. This paper seeks a deeper comprehension of the recent advancements in EMSs for FCHEVs. It offers insights that can facilitate a more comprehensive grasp of the current state of research in this field, aiding researchers in staying up to date with the latest developments. fuel cell hybrid electric vehicle; topology; energy management system; fuzzy logic; ultracapacitor; battery; control system; power converter; degradation +
Footnote †: journal: Applied Sciences  
energy efficiency [3]. It offers a longer range with a quicker refueling time than an electricity vehicle (EV) [4]. Moreover, hydrogen fuel cells have a higher energy density than current lithium-ion batteries used in most electric vehicles. However, the fuel cell system falls short in supplying the necessary power during dynamic states like start-up, climbing, or acceleration, because the reaction gas response rate cannot keep up with changes in load [5]. Additionally, chemical energy is directly transformed into electrical energy within the operation of the fuel cell system (FCS), allowing for one-way power output, making it impossible to retain the energy produced during slowing down or braking [6]. Deficiencies in the FCS can negatively impact a FC vehicle's economy, dependability, and durability [7]. To counteract these issues, FCEVs are often coupled with a supplementary energy storage system, like a battery or ultra-capacitor (UC), to form a FCHEV system [8; 9; 10]. The hybrid system can successfully address the challenges previously mentioned. However, the presence of many energy sources leads to a more complex working mode for the power system. As a result, developing an efficient, reliable, and stable method for utilizing numerous energy sources has become a key technology for the FCHEV system [11; 12]. This key technology, known as the energy management system (EMS), has a direct impact on the optimal operating point of each energy source to fulfill the demand for electricity. Additionally, the EMS helps to distribute power effectively in response to changing demand, reducing fuel consumption, improving the system's efficiency, and extending the FCHEV's operational life [13]. Hence, studying EMSs is vital for the FCHEV. This review focuses on analyzing the current research that pertains to the structures and energy management mechanisms adopted for FCHEVs. An overview of different forms of vehicle technology is given in Section 2.