Research On Identification And Control Method Of Fuel Cell Water State Under Vehicle Environment

Fuel cell vehicle has the advantages of short fuel filling time and long cruising range,which is an important method to promote China’s low-carbon energy transformation.However,the lack of reliability and durability of fuel cell still limits its commercialization.And fuel cell water management is a key bottleneck.In order to improve the comprehensive performance of fuel cells in vehicle application,it has important scientific and engineering value to research the identification and control method of fuel cell water state under vehicle environment.Therefore,aiming at the vehicle application of high-power fuel cells,this paper mainly focused out the following four aspects of research work:Research on identification method of fuel cell water state based on electrochemical impedance spectrum(EIS).In order to identify the fuel cell water state through EIS,the variation rules of different polarization loss under different water state of fuel cells were obtained from the reaction mechanism.On this basis,the experimental equipment was built and the EIS data under different operating conditions were obtained by taking the large area fuel cell as the test object.Combined with the mechanism and experimental data,based on the existing ohmic impedance to identify whether the fuel cell is dry,a water state identification method is proposed to identify whether the fuel cell is flooded by using the change trend of the mass transfer impedance.Finally,the method is applied in the field of the optimal operating temperature search and the low-temperature cold start purging.Development of on-board EIS measurement device.In order to apply the water state identification method based on impedance spectrum to vehicle field,an AC excitation module which’s suitable for various power system architectures was designed.The working characteristics of fuel cell DC/DC in parallel with AC excitation module were analyzed,and the current acquisition scheme of impedance inspection module was proposed.The hardware circuit and impedance calculation method of impedance inspection module are designed.The experimental results show that the designed device has the same test effect as the standard instrument.Research on identification method of fuel cell water state based on anode fluctuation voltage.In order to meet the requirement of water state identification of fuel cell system without EIS measurement device,it is found that the fuel cell voltage fluctuates periodically with the periodic action of hydrogen purge valve.Based on this phenomenon,the fluctuating voltage model of hydrogen purge process of fuel cells was established,and the amplitude of fluctuating voltage increased with the increase of water content.Sym20 wavelet transform was used to extract the characteristics of fluctuating voltage,and the energy intensity of fluctuating voltage was used as the diagnostic index of water state.The method was verified under steady and dynamic conditions of the fuel cell system.The results show that the energy intensity of the fluctuating voltage is strongly correlated with the water state and has the same sensitivity as HFR.Research on water state control strategy of fuel cells under typical operating conditions.In order to reduce the fluctuation of fuel cell water state under typical operating conditions,a calculation model of fuel cell water state was established.Based on this model,the effects of different fuel cell system architectures and operating conditions on water content of fuel cells were analyzed.Taking the fuel cell system without humidification as an example,the optimal control strategy of water state was proposed under the single interference factor and multiple interference factors respectively with the help of an optimal control strategy of water state corresponding to the dynamic adjustment of operating condition parameters.The experimental results show that the proposed method can effectively reduce the fluctuation of water state in the start-up phase and ensure that the fuel cell is in normal water state when it reaches the stable operating point.The main innovations of this paper are as follows: Taking large area fuel cells for vehicle application as the research object,a water state identification method based on the variation trend of mass transfer impedance to identify whether fuel cell is flooding is proposed,and on-board EIS measurement device is developed.Taking the fuel cell system as the research object,a water state identification method based on the fluctuating voltage energy intensity of hydrogen removal process was proposed.For the typical working conditions such as vehicle environmental heating engine,plateau and environmental dew point changes,an optimal control strategy of water state by dynamic adjustment of operating condition parameters was proposed.In this paper,water state of high-power fuel cells for vehicles is identified and controlled successfully,which provides technical support for improving the fuel cell power generation efficiency,lifetime and environmental adaptability.