Research On Vehicle Fuel Cell Internal Resistance Test System Integrated In Large Step-up Ratio DC/DC

Fuel cell is clean and environmentally friendly with high energy conversion rate,and the on-line monitoring of its internal resistance is the key to ensure the safe and efficient work of the fuel cell.On-line monitoring by using Boost converter ripple can reduce equipment volume and test time.When fuel cell is used in certain on-board applications(such as extended-range fuel cell vehicles),its output voltage is low,so DC/DC circuit with large boost ratio is needed to obtain high voltage to drive the motor.In order to solve this problem,this paper designed a DC/DC converter with large boost ratio.With AC excitation signal source integrated into the DC/DC converter,the test system is more suitable for fuel cell vehicles with limited volume and high voltage level requirements.The main research contents of this paper are as follows:An on-line internal resistance test scheme for vehicle fuel cell integrated with high boost ratio DC/DC converter was proposed.The internal resistance model of fuel cell and its Nyquist characteristic curve were analyzed;According to the output characteristics of fuel cell and the demand of fuel cell vehicles,an on-line EIS(Electrical Impedance Spectroscopy)detection structure was designed by introducing triangular wave small signal required for test into high boost ratio converter.A DC/DC circuit topology for on-line internal resistance test of fuel cell with high boost ratio was designed.By choosing reasonable internal resistance parameters and combining with test principle,a cascaded two-stage boost topology between Boost circuit and DC/AC/DC full-bridge converter was designed.Boost converter realizes the introduction of small disturbance signal,and the full-bridge converter of the latter stage can obtain higher boost ratio.And the hardware circuit of the main controller was designed according to the requirements of the test system.A DC/DC converter model with high boost ratio was established.The simulation results show that the test system can achieve high boost ratio and high precision internal resistance.The test circuit topology was modeled and the main circuit controller was designed;The influence of leakage inductance of high frequency transformer on circuit was analyzed emphatically,using the RCD absorption circuit to suppress the spike voltage.The correctness of theoretical analysis is verified by simulation and experiment.A simulation experiment platform was built in the joint simulation environment of MATLAB/PLECS to test the internal resistance of high boost ratio converter by introducing triangular wave signal.And the results show that the designed scheme is correct and feasible.Fuel cell internal resistance examination platform was built to verify the system designed in this paper.According to the voltage and current of the experimental platform,the circuit parameters were calculated and the appropriate components were selected;The software program of the controller of TMS320F28335 was designed and the waveform obtained from the experiment was analyzed;The experimental results were compared with the theoretical results,and the causes of the errors were analyzed.Experiments show that the accuracy of the internal resistance measured in the DC/DC converter with large boost ratio can reach more than 95%,and the effect of triangular wave micro-current signal on the normal operation of the system is small,which proves that the scheme is correct and feasible.This method can greatly reduce the volume of the test system,shorten the test time,and provide a new idea for on-line internal resistance test in engineering.