Research On PEMFC Tempeature And Humidity Performances And Control Rules Based On Internal Resistance Detection

Proton exchange membrane fuel cell(PEMFC),known as "the most promising vehicle energy conversion device",has become a new hot-spot due to environmental friendliness.PEMFC research involves multidisciplinary knowledge of fluid kinematics,electro-chemistry,material science,automatic control,etc.PEMFC stack control system is a nonlinear strongly-coupled system whose output characteristics are determined by the inside temperature and humidity.Temperature and humidity within the stack are difficult to be measured directly due to the tightness of the stack,while the external parameters could not characterize the actual working conditions inside the stack.Choosing an appropriate stack characteristic parameter as the control index is a key to ensure the control effect,the operating conditions decoupling of temperature and humidity.The adjustment of stack control variable is an important part to realize the decoupling control of temperature and humidity.Changes of temperature and humidity is the reason for the change of internal resistance of stack,while the resistance as a stack characteristic parameter is the root cause of the change of external output performance.Currently,there are many testing methods of internal resistance.Most of them can not satisfy the existing requirements of measurement and accuracy requirements,and some methods have enormous damage to PEMFC stack.According to earlier research,a method based on improved EIS can accurately measure each resistance parameters in stack.Establish mechanistic models by the temperature and humidity characteristic relationship between the resistance and the operating conditions.Although the traditional decoupling method can be used to decouple the partial control variables,it is too intricate to decouple the temperature and humidity which involves many control variables and complex variation characteristics.Aiming at operating conditions coupling defects and control method of water-cooled PEMFC,this paper choose the correlation coefficient as a new entry point and detect internal resistance instead of external parameters to improve thedefects of traditional methods.Based on the inner resistance,mechanism characteristics of control variables and operating conditions of temperature and humidity,researches has been done to get the inter-variable correlation parameter,analyze the mechanism relationship and the experimental data of PEMFC stack between the control variables and operating conditions.This paper studies the complex coupling relationship between operating conditions and control variables,selects the main and auxiliary control variables of PEMFC stack in different output characteristics.According to the relationship and variables above,relative mechanism model of internal resistance and management of water and heat can be established,which determines the optimal operating conditions and basic principles of temperature and humidity at different output stages.The feasibility of the model is verified by experiments,whose the results show that the model can realize the decoupling of temperature and humidity of PEMFC stack,which means the model is correct and feasible.At the same time,it is recognized that the research process of correlation degree is similar to the design process of fuzzy controller,and a fuzzy control method based on improved membership functions is proposed.