## 1 Introduction  
Nowadays, environmental pollution becomes an urgent issue that undoubtedly influences the health of humans and other creatures living in the world. This situation has spurred more studies to come up with renewable energy sources as a long-term solution for human survival. According to research by the International Energy Agency (IEA), from 1990 to 2018, renewable electricity generation rose rapidly with wind, solar photovoltaic (PV), and hydrogen resources. In which, the growth of hydrogen energy increased 97.3% and was forecast to remain the world's largest source of green energy [1]. It can be seen that hydrogen is one of the essential elements in the energy structure as well as has great potential to be widely used in the 21 st century. As the most proper and effective system using hydrogen, the PEMFC has been attracted as a potential candidate to combine with conventional energy devices such as a battery (BAT) or a supercapacitor (SC) [2] in hybrid systems. The lower operating temperatures and higher energy conversion are the leading properties of the PEMFC in comparison with other types of fuel cells [3]. However, slow dynamic response and incapability of recovering exceeded energy have become the key obstacles for widespread applications that use the PEMFC as a standalone energy source because the variation of load demand may result in fuel starvation, membrane drying issues, blooding; thus, causing the degradation of PEMFC lifetime [4; 5; 6]. Hence, it is necessary to develop an integration of the PEMFC with other interconnected electrical storage devices such as BAT and/or the SC. For example, the integration of PEMFC with both BATs and SCs was investigated in many applications such as hybrid electric vehicles [7; 8], construction machinery [9; 10], and hybrid tramway powertrain [11; 12], and some other fields of automation or power systems. This hybrid configuration can exhibit better performance, reduce the system size, solve the problem of fuel economy, and prolong the lifespan of energy devices. However, the problem of effective management should be considered for complex hybrid power systems. Therefore, the development of an EMS is required for appropriate energy assignment between the PEMFC and the energy storage system to match the required power of the powertrain. Following the historical literature for the hybrid tramway's EMS design, optimization-based methods have been successfully applied in several research works; however, the local optimal solutions of real-time optimizations or inconvenience of off-line computation in global optimizations are existing issues to address when implemented on hybrid systems in practice. Besides, most studies on optimization for the hybrid tramway have been implemented in two-device configurations such as BAT-SC, FC-BAT, and FC-SC because it is a challenge to achieve optimal objects for three-device configurations under complicated power-sharing strategies [13; 14; 15]. Thus, rule-based EMS can be regarded as a simplified and effective selection to design efficient power distribution strategies for the hybrid system, especially the high-power system such as tramways, excavators, and so on. In [16], a power flow control strategy was developed for a switcher locomotive-powered PEMFC-BAT-SC hybrid system to maintain levels of power demand while keeping the appropriate state of charge (SOC) on the energy storage devices (ESDs). In [17], [PERSON] et al. presented an adaptive EMS based on states of the PEMFC and BAT to distribute the load power demand for each energy source. This strategy could ensure the power performance and satisfy the driving cycle of the hybrid tramway system under different working conditions. Developed from the work [17], an operational mode control and cascade control loop were carried out in [18]. The simulation results showed that the proposed EMS was able to produce an appropriate power for the traction load while keeping the SOC of ESDs and the DC bus voltage at the desired level.