Study On Micro Direct Methanol Fuel Cell Systemic Model

Nowadays,the functions of mobile electronic products are becoming more and more complex,and the power consumption is also extremely increased.There is an urgent need for a mobile power source capable of continuously outputting a relatively large power.In this application context,Micro Direct Methanol Fuel Cell(?DMFC)is considered to be one of the most competitive and promising new energy sources because of no charging,high output power and energy conversion efficiency,environmental impact,and easy access to fuel and storage.?DMFC cannot be used directly in the form of a single unit.In practice,it must be composed of a stack system.However,the traditional ?DMFC model has two main problems when designing the system: First,the traditional model has a long simulation time due to complexity and large computational complexity,resulting in low efficiency of system design.Second,the traditional model does not consider the impact of different loads on system energy conversion,making the designed system larger.energy loss,the energy conversion efficiency is low.This paper has carried out the following research work on the above issues.Through the simplification and theoretical derivation of the system function,an equivalent circuit model(ECM)of the grey-box ?DMFC unit was abstracted.The model was used to simulate the output characteristics,internal mass transfer and electrochemical reaction of the ?DMFC unit.The simulated results showed that the ECM of the ?DMFC unit broke through the mathematic physical model of COMSOL in designing the efficiency of the ?DMFC unit,which could shorten the simulation time by an order of magnitude while ensuring the accuracy of the simulation,and solved the low efficiency of the current model design on ?DMFC unit.The ECM of the ?DMFC could effectively describe the working process of the ?DMFC unit,and the correctness of the simulation results was verified by experiments.The ECM of ?DMFC could also be equivalent to electronic devices,which provided a theoretical basis for the establishment of ?DMFC system level model.Based on the ECM of the ?DMFC unit,the system level model of the ?DMFC stack was established.The ?DMFC stack systemic model was used to simulate the ?DMFC stack system including ?DMFC stack,voltage regulator and load.The results showed that the change of load power had a great influence on the energy conversion efficiency of the ?DMFC stack system.Refueling based on the load power adjustment system could effectively improve the energy conversion efficiency of the ?DMFC stack system.According to the simulated results of the system model,the fuel concentration with the highest energy conversion efficiency under each load power was obtained.According to the simulated results of the system-level model,a method for adjusting the fuel supply based on the load change was proposed.As the load changes,the system maintained the fuel concentration with the highest energy conversion efficiency by controlling the refueling speed,which improved the energy conversion efficiency of the whole system.Based on the refueling method proposed in the system level model research,a ?DMFC stack system was designed and implemented.The experimental test and analysis of the ?DMFC stack system were carried out.The results showed that the energy conversion efficiency of the ?DMFC stack system increased with the increase of load power.The simulated relationship between the energy conversion efficiency and the load power was validated experimentally.Compared to a conventional system with a constant supply,the DMFC stack system based on load-adjusted fuel supply increased the energy conversion efficiency by 9% and 8% while driving a transient changing load of 0.2 W and a continuously varying load of 0.3 W,respectively.The effectiveness of the systemic model proposed in this paper in the simulation design of the ?DMFC stack system had been experimentally verified,and the energy conversion efficiency of the ?DMFC stack system had been improved.