Study On Modeling And Power Splitting For Multiple Module Fuel Cell System

Durability and cost of vehicle-mounted fuel cell are two important factors that hinder the commercialization of fuel cell vehicles.Due to the manufacturing process,fluid distribution and temperature distribution each single fuel cell or module is not consistent.Thus state of health in each fuel cell module is not the same,a few single cell or module can not bear high load.So power splitting should consider the consistency of each fuel cell module and decide the power of every module according to the state of health of each module.Then each module will work in optimal area,so as to improve the fuel cell system durability and efficiency.In this dissertation research subject is multiple module fuel cell system which consist of some fuel cell module and supercapacitor.Some key problems in system modeling and power allocation are studied.The main research results are as follows:By using the energy macro representation(EMR)each part of the model in single fuel cell system is analysed and EMR model of single fuel cell system is established.The structure of multiple module fuel cell which include electrical structure,thermal structure and fluid structure is analysed.EMR model of multiple module fuel cell system is built by combining the EMR model of supercapacitor,undirectional DC/DC,bidirectional DC/DC,and permanent magnet brushless motor with EMR model of multiple module fuel cell.Control strategy for series and parallel structure in multiple module fuel cell system is studied.Firstly,control strategy for series multiple module fuel cell system is proposed.This strategy can cut off the faulted fuel cell module through the fault switch,the rest of the fuel cell module can continue to work.According to the model of DC/DC converter control model and the control objective,the master-slave model predictive control strategy in parallel multiple module fuel cell system is proposed.In order to reach the requirement for real time optimization computing in every sample single step neural network optimization method is proposed.The simulation results show the effectiveness of the method.Power splitting strategy in multiple module fuel cell system is proposed based on multiple mode passivity-based control.Power curve of the typical operating condition and average power is plotted to prove that switch of multiple fuel cell module is necessary and feasible.After working mode of multiple module fuel cell system is analysed,flow chart of mode switching in different working mode is provided.According to passivity-based control method port controlled Hamiltonian model is built and state variable equilibrium in every mode is calculated.nonlinear controller of multiple mode passivity-based control is designed and the stability of passivity-based control is proved.A fuel cell equivalent circuit model is built and the corresponding relation between electrochemical impedance spectra and equivalent circuit model is analysed.The overall scheme of test system of fuel cell resistance is presented by using ripple wave modulation to measure fuel cell resistance.The state of health(SOH)of fuel cell is calculated by measuring fuel cell resistance online.According to SOH of each fuel cell module detection to health,two problems are considered.One is how to split the power of working fuel cell module at the same time.Another is how to choose the switching sequence of fuel cell module.Then power splitting of multiple module fuel cell system is studed based on SOH test online.Stress concept is advanced to test the frequency of fuel cell power.Wavelet analysis method is used to deal with power curve obtained in advance.The low frequency section of the results is splitted to the fuel cell in order to reduce stress and improve fuel cell's life.Semi-physical simulation platform of multiple module fuel cell system is built based on CPU and field programmable gate array(FPGA).Models of fuel cell and supercapacitor are implemented in Industrial Personal Computer by using fourth-order Runge-Kutta method.models of undirectional DC/DC,bidirectional DC/DC and permanent magnet brushless motor are implemented in FPGA by using parallel module method.Five typical working condition is used to validate the effectiveness and feasiblity of proposed power splitting strategy.In summary,some problems which are model of multiple module fuel cell system,series and parallel control strategy,power splitting strategy based on multiple mode passivity-based control and fuel cell's SOH are studied and reveal their research ideals.The related calculation and simulation results verified their feasibility and effectiveness.This results can provide reference for the further research in power distribution and durability of fuel cell system.