Research On Fuel Cell System Cluster Efficiency Optimization

With the increasing of global environmental pollution and energy exhaustion,fuel cell as a promising energy technology,especially proton exchange membrane fuel cell(PEMFC),have been widely used in distributed power station,electric vehicles,rail transit and other fields.For high-power applications such as rail transit,the reliability of a fuel cell system cannot meet the requirements,and fuel cell system cluster structure consisting of multiple fuel cell systems in parallel must be used.Because each subsystem has its own work efficiency curve,it needs to coordinate the allocation of demand power between each subsystem when the load changes dynamically,and by controlling the startup,shutdown and load-unload actions of each subsystem to ensure that the cluster operates at a higher efficiency range under the condition of meeting the demand power.Therefore,this paper mainly focuses on the design and construction of a 30 kW water-cooling fuel cell system test platform,the modelling and experimental verification of fuel cell system efficiency,the efficiency optimization method of fuel cell system clusters,and the startup-shutdown and load-unload strategies of fuel cell system clusters.the main research content and findings are as follows.Based on the analysis of the structure and working principle of the PEMFC system,a 30 kW water-cooling fuel cell system test platform was independently built.This paper gives the platform construction plan,and the main auxiliary equipment and functional units such as PEMFC stack module,hydrogen supply system,air supply system,cooling circulation system,DC/DC,electronic load,data acquisition and controller are given for selection.Based on the hardware platform,a complete system control program and upper computer visualization program were written based on PLC controller and Labview software,and the program control and operation flow were given,which laid the foundation for follow-up study.A semi empirical and semi mechanism fuel cell system efficiency model of 30 kW system test platform was established,which consisted of five sub-modules: fuel cell thermodynamic efficiency model,fuel cell stack power model,air compressor power model,cooling pump power model and cooling fan model,Based on the 30 kW fuel cell system platform,the modle simulation results was compared and verified by the experimental data in different operating conditions.Aiming at the efficiency optimization problem of fuel cell system cluster,an FCSC efficiency model consisting of three fuel cell subsystems was built on the basis of the 30 kW fuel cell system efficiency model,and the Lagrange relaxation algorithm and the Disturbance variable load method were proposed to solve FCSC efficiency optimization problems.The principle of the Lagrangian relaxation method is adding complex constraints to the objective function through the form of Lagrangian multiplier,which greatly reduces the difficulty of solving the original system cluster efficiency optimization problem.The Disturbance variable load method is mainly aimed that the power of the fuel cell cluster system can be optimally distributed through the system parameters identification under the variable system conditions and external parameters.Finally,based on the simulation results of the two optimization algorithms,a startup-shutdown and load-unload control strategy for the actual FCSC system is proposed,and the calculation method of startup point for the cluster was given.Compared to the two traditional distribution methods,it is ensured that the fuel cell system cluster operates in the higher efficiency range throughout the entire power range.