Towards cost mitigation for fuel cell electric vehicles: Recent progress and challenges on combined optimization of powertrain sizing configuration, speed planning and energy management strategies

Fuel cell hybrid electric vehicles (FCHEVs) express the huge potential in realizing green and low-carbon transportation, but high total cost in vehicle's purchase and operation stages still prevents their rapid and large-scale commercialization. Beside to satisfying the propulsion power demand, energy management strategies (EMS) attempt to save hydrogen, to extend fuel cell lifetime and to mitigate vehicular operating costs through optimizing the outputs of energy sources. Nevertheless, the discrepancies between the standard speed-time dataset for strategy design and the real-world ones for testing may seriously compromise EMS performance. In addition, powertrain component size (e.g. the capacity of battery, the maximal output power of fuel cell, etc.) directly influences FCHEVs' manufacture cost and also put constraints on output feature of energy sources, thereby affecting the power-allocation performance. In this case, focusing on either one of aforementioned three aspects would not be effective in bringing down FCHEV's operating costs, thus indicating the necessity of developing a combined optimization framework that consider vehicular EMS, speed planning and component sizing concurrently. This paper starts by analyzing FCHEVs' powertrain structure and models and follows by a comprehensive review on state-of-the-art approaches and optimization frameworks for EMS, speed planning and sizing design. Then, a case study on combined optimization of sizing-EMS combination and speed planning-EMS combination is conducted. Finally, the major challenges and future prospective of combined optimization are summarized. This paper not only provides a literature review for readers but also a guideline for prospect designers in the field of FCHEV powertrain design and control.