Research On Software Of Fuel Cell Impedance Online Measurement System And State-of-health Monitoring

Fuel cell is considered a type of new and most promising energy converter in the 21st century, because of its determining environmentally friendly feature. Currently, fuel cell systems' lower stability, reliability and durability are major obstacles to their large-scale commercialization, which has become one of the key research fields and aspects of fuel cell technology. Fuel cell's impedance reflects its power generation efficiency, and measuring it on-line is very useful and helpful for fuel cell's performance analyzing, operation controlling and fault diagnosing. Therefore, in this thesis, the software of fuel cell impedance on-line measurement system was studied and designed to measure fuel cells' impedances accurately, intellectually and automatically. Furthermore, a method based on fuel cell's impedance to monitor fuel cell's state-of-health (SOH) on-line was also studied. The main research contents are as follow:Firstly, the general architecture of the fuel cell impedance on-line measurement system was analyzed. The scheme and hardware structure of the system which based on electrochemical impedance spectroscopy (EIS) method were analyzed and studied in detail, which put a solid foundation on the follow-up software design.Secondly, much work was focused on the research and development of the software of fuel cell impedance on-line measurement system. The general architecture of the software was established based on its design requirement analysis, and program modules of both the main controller and data acquisition units which including the measurement controlling algorithms, data acquisition program and communication protocol of SCI and CAN were designed and developed one by one. On the end, an equivalent circuit model was built to take a joint test of the system and the test results were also analyzed.Error compensation and interference prevention designs were essential to the software of fuel cell impedance on-line measurement system. In order to improve the measurement accuracy and ensure the stability of the system, major sources of error which influence the system's measurement accuracy were analyzed, compensated and on-line corrected, and several software anti-interference methods were also performed to enhance the system's reliability. Finally, a method based on fuel cell's impedance to monitor its SOH was studied. The selection of fuel cell's impedance model and method of impedance data processing were discussed to process EIS data in real-time and calculate parameters of each elements of fuel cell's impedance model on-line. By analyzing the impedance characteristics of fuel cell's three typical SOH including normal, flooding and drying out with respect to its water content, a SOH on-line monitoring method based on linear discriminant analysis (LDA) which takes ohmic resistance, polarization resistance and diffusion resistance as its three monitoring indicators was proposed, its linear discriminant function and criteria were established, and simulation was performed to verify the effectiveness of the SOH monitoring methods.The designed software could meet the needs of the task of measuring each single fuel cell's impedance and voltage for different power stacks on-line and in real-time with its characteristic of extreme stability, high accuracy and strong real-time, and satisfy the requirements of system design.