| The shortage of resources and the deterioration of environment are the main problems in modern society.In order to solve these problems,people continue to research on new energy sources.Among the new energy sources,fuel cell has become one of the most promising new energy sources with the characteristics of no pollution,low noise and high efficiency.At present,the research on fuel cell mainly focuses on the material and chemical aspects of fuel cell stack.The research on modeling and control methods of fuel cell system is still in the developing stage.Fuel cell system consists of battery stack and its subsystems.Fuel cell subsystem includes temperature control system,humidity control system and gas supply system.Gas supply system is used to provide the reactants.Therefore,this paper takes gas supply system as the research object.In the air supply system,air compressor is used to control air flow.The inadequate supply of air flow will lead to oxygen shortage and low output efficiency.Oxygen excess ratio can reflect the situation of gas supply.It is an important index to measure whether the fuel cell system works properly.This paper realizes the control of peroxide ratio by adjusting the voltage of air compressor to control the input flow of oxygen.The main research contents and results are as follows.(1)Fuel cell stack model and gas supply model are established based on fuel cell theory and ideal gas equation.Through the analysis of the oxygen excess ratio when the maximum net power value is obtained,the equation of the oxygen excess ratio about the load current is obtained.The model is built on MATLAB and simulated.By analyzing of the simulation results,the influence of load current surge and drop on the oxygen excess ratio is analyzed.The control effect of air compressor voltage change on the oxygen excess ratio is verified.(2)The basic performance control of fuel cell system is realized by using PID.The deviation of air compressor speed during operation is taken as the input of the PID controller,and the voltage of the air compressor is taken as the output of the PID controller.By adjusting the parameters of PID,the effective control of the oxygen excess ratio has been achieved preliminarily.Aiming at the problem of fixed parameters of the PID controller,the fuzzy control is used to improve the PID control,and the fuzzy PID controller is obtained.Compared with the PID control,Fuzzy PID controller obtain better control effect.(3)Considering the requirement of steady-state performance in the process of oxygen excess ratio control,sliding mode control is adopted.The formula of the deviation between compressor airflow is selected as the sliding surface.Super-spiral algorithm in the second-order sliding mode is adopted to control the oxygen excess ratio.The simulation results show that the sliding mode control can improve the stability of the oxygen excess ratio control.(4)Considering the voltage constraints of air compressor,the model predictive controller is used to control the air compressor.According to the need of model predictive control,the nonlinear system of fuel cell is linearized at the working point.The model is built on MATLAB and simulated.The simulation results show that the model predictive control has better dynamic and steady-state performance than other control algorithms.The net power output is obviously higher than other control algorithms,and the voltage of air compressor can be controlled within the constraints.The overall control effect is better. |
PDF Full Text Request