Development and Evaluation of a Degree of Hybridisation Identification Strategy for a Fuel Cell Supercapacitor Hybrid Bus

Abstract

Fuel cells (FC) are a clean energy source that are capable of powering a vehicle’s electrical energy requirements whilst providing zero operating emissions. In this study, a full-scaled computer model FC/supercapacitor (SC) hybrid has been developed to investigate the performance of the hybrid propulsion system under real-world performance conditions. A control strategy focused on maintaining a constant FC output at a user-defined value has been developed and applied to the FC/SC hybrid model. Driving cycles collected from a practical double-decker bus have been utilised to evaluate the developed model. It has been demonstrated that the proposed control strategy is capable of maintaining a constant and stable FC output while meeting a real world dynamic load. Based on the obtained results, a general strategy to identify the degree of hybridisation between the FC and the SC in a FC hybrid system has been developed and demonstrated.

Investigation on the Impact of Degree of Hybridisation for a Fuel Cell Supercapacitor Hybrid Bus with a Fuel Cell Variation Strategy

“…The FC/SC hybrid configuration is shown in Figure 2. The originally proposed FC/SC operation strategy is to keep the FC at a constant pre-defined output power while using the SC to cover any transient power demand, as detailed in [32]. In this system the balance of power between the FC, SC and load is controlled on the common busbar linking these components.…”

“…In this system the balance of power between the FC, SC and load is controlled on the common busbar linking these components. This method has been validated and tested in [31,32] and was shown to perform well under transient conditions whilst…”

“…In this system the balance of power between the FC, SC and load is controlled on the common busbar linking these components. This method has been validated and tested in [31,32] and was shown to perform well under transient conditions whilst maintaining a stable busbar voltage (630 V in this case). Since the voltage is maintained at a constant value, the power balance is directly controlled by controlling the magnitude of the current and can simply be written as:…”

“…The output power of the FC and boost converter (P fc_out ) is defined as 110% of the average power requirement of the bus duty cycle (P load ) with the additional 10% included to account for the losses in the SC buck/boost converter and is maintained at a constant value. The SC was sized by considering the cumulative energy change over the course of the drive cycle, with a 20% margin over the magnitude of cumulative energy change chosen as the SC size, further details of this can be found in [32]. This strategy has been proven capable of providing a reasonable estimation of the required degree of hybridisation for a certain duty cycle.…”

“…This approach additionally allows for the assessment of the potential for downsizing the FC stack. The work detailed in this paper is a continuation of the research presented in [30][31][32] and further considers the evaluation of the degree of hybridisation through improvement of the control strategy. In the previous work, a FC/SC hybrid propulsion system had been developed, constructed and simulated.…”