Development of an energy management system for fuel cell/lithium-ion battery hybrid electric vehicles

Abstract

The growing interest in fuel cell hybrid electric vehicle (FCHEV) is largely supported by the decline in fossil fuel production and the need to operate eco-friendly transport system. This interest has triggered significant research on various aspects of FCHEV. Again, environmental pollution associated with internal combustion engine (ICE) vehicles, advancement in fuel cell technology, improvement in power electronics, and cutting-edge energy management systems (EMSs) are additional reasons why FCHEV has received significant attention by both the transportation and environment sectors including researchers and vehicle manufacturers. However, having an effective EMS improves the performance of fuel cell hybrid electric vehicle by enhancing the optimisation of individual components within the system. However, to overcome the complex task of optimisation, factors such as component degradation, straight-line performance, fuel consumption and driveability must be considered in detail. Hence, the primary purpose of EMS in a FCHEV is to reduce the electrical stress exerted on the fuel cell, increase the productive lifespan and to minimise the fuel consumption. This is informed by the fact that the durability and cost of fuel cell stack is the main obstacle preventing massive adoption of FCHEVs. Therefore, an EMS is designed and developed under the MATLAB/Simulink environment and Typhoon HIL software for Real-Time simulation primarily to optimise power regulation and distribution for a fuel cell/ lithium-ion battery hybrid electric vehicle. The EMS is developed to exploit the advantages of fuel cell and lithium-ion battery hybridisation for improved performance while offsetting the individual setbacks. The system consists of a 100 kW proton exchange membrane fuel cell stack (PEMFC), DC-DC boost converter, 30 kW lithium-ion battery, DC-DC bidirectional converter, an inverter, permanent magnet synchronous motor (PMSM), vehicle body (including chassis, tires, gears) and controllers that ensured effective power distribution. To demonstrate the effectiveness of the developed EMS in terms of power distribution and performance, it was implemented using Federal Test Procedure-75 (FTP-75) drive cycle to highlight transient load and regenerative braking. In addition, the EMS is modelled with fuel cell control component and battery control component respectively using PI controller, battery SOC and power demand by the electric vehicle (EV). This was implemented using external voltage loop and internal current control loop of the bidirectional converter and current loop control and the voltage loop of the DC-DC boost converter. The results showed a precise response to the load demand and improved performance throughout the drive cycle. The lithium-ion battery was able to supply power during transient loads when the power supply from the fuel cell was less than the load demand. Furthermore, validation of the MATLAB/Simulink result was required to authenticate it by implementing the model in real-time using Typhoon HIL software. The real-time result was similar to the ones obtained in MATLAB/Simulink environment thereby confirming the effectiveness of the EMS.