UBC Theses and Dissertations
Design and implementation of microcontroller-based direct methanol fuel cell/lithium polymer battery hybrid energy management system Chen, Di
The Direct Methanol Fuel Cell (DMFC) has been considered as one of the competitive alternatives for battery technology as it has much higher energy density, faster recharging and does not require complicated control systems like a fuel reformer or compressed gas tank as needed by a hydrogen fuel cell. However, current DMFC technology suffers from the low power density caused by low reaction rate and undesired “methanol crossover” issues, which brings a big challenge for its application in practical systems. This thesis presents a practical design and prototype development of a DMFC/battery hybrid energy management system, which can be provided as one possible solution for the low power and cold start issues. First of all the existing fuel cell hybrid system schemes and design of the auxiliary units (BOP) are surveyed and compared. Based on the analysis above a microcontroller-based DMFC and Lithium Polymer Battery hybrid system is proposed. After that a novel “Battery-Current-Based Hybrid Control (BCBHC)” is proposed to provide active load sharing and proper battery charging and protection. The DMFC will follow the average battery current by neglecting the battery current transients and charge the battery by following the Constant-Current and Constant Voltage charging scheme when possible. A variety of battery protections, such as overcharging, overcurrent and charging current limitation, are implemented by the BCBHC and protection circuit. A detailed system design and modeling are then presented. The models are developed and simulated in PSIM. The simulation results are analyzed and showed the validity of proposed hybrid control. At the end a prototype hybrid EMS controller board has been implemented to further validate the hybrid system design. The dynamic behavior of DMFC/Battery hybrid system is examined and tested under a series of load experiments. The measured results have proved the feasibility and stability of the designed hybrid control.
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