Performance Degradation And Fault Evolution Mechanisms Based SOFC System Modeling And Control Optimization

Solid oxide fuel cell(SOFC)technology is considered as one of the most promising green power generation technologies in the 21 st century due to its advantages of cleanliness and high efficiency.After decades of development,it has gradually become mature,but high cost and short lifetime are still the bottlenecks hindering its large-scale commercial application.When operated in a long time,the performance of the system will decline and gradually evolve into a fault,which will lead to the changes in the dynamic and static characteristics of the system.The original control system design will face problems such as parameter mismatch and control failure.Based on the 1kW steam-reforming SOFC independent power generation system as the research object,in-depth research on the mechanisms of performance degradation and fault evolution in SOFC systems was conducted.The SOFC multi-mode model considering performance degradation and fault evolution mechanisms was developed for the first time in the field of SOFC and a complete health evaluation system was designed as well,based on which SOFC system control optimization was realized.First of all,the mechanisms of SOFC system performance degradation and fault evolution were analyzed,and the common degradation and fault types were found.Then the experimental data and phenomena from long-term test for SOFC systems were utilized to describe the performance degradation factors and fault evolution process physically.Subsequently,SOFC system mechanism model including multiple performance degradation and fault modes was developed based on Stateflow platform and verified by experiments.Then,the optimal operation point(OOP)of SOFC system under the condition of performance degradation was defined,and the method of acquiring OOPs in a fast way on the basis of genetic particle swarm optimization algorithm was designed.After obtaining OOPs in all the cases,they were compared with those obtained in the original state to analyze the drift characteristics.In addition,the dynamic and static responses of the SOFC system with different fault parameters in different fault situations were simulated,which would provide significant support for the future work of early fault identification and treatment.Based on the optimization analysis above,the key parameters and functions were selected and defined to devolop the health evaluation system of the SOFC system.Aiming to the SOFC system control architecture based on TS model and constrained generalized predictive control(TS-CGPC),control parameters were optimized according to the health evaluation parameters.Through the comparison between the simulation results before and after the optimization of controller,it was found that the improved controller could maintain the system safety and the optimal system efficiency under the condition of multiple operation constraints,and avoid the efficiency reduction and failure of the SOFC system caused by the mismatch of control parameters.Through the function fitting of system health degree to reformer health degree and stack health degree,five types of faults could be effectively identified,and the basic method of early fault pretreatment and post-treatment was summarized at the end.This thesis developed the modeling method and analysis system for SOFC systems based on the mechanisms of performance degradation and fault evolution,revealing the essential characteristics of SOFC system performance degradation and improving the design of system thermoelectric coupling controller,which would provide strong theoretical support for SOFC system operation with high efficiency and long lifetime.