Energy Optimization Control Of Solid Oxide Fuel Cell-internal Combustion Engine Integrated CHP Unit

Solid oxide fuel cell（SOFC）is a new type of power energy device,and it has attracted extensive research attention due to its advantages of high power generation efficiency,more available heat energy,high Fuel efficiency,pollution-free emission and low dependence on external equipment.SOFC exhaust gas is rich in thermal energy,which can be directly provided to users,or can be further generated by steam turbine（GT）and other equipment,thereby improving the energy utilization rate of the system.In addition,methane with high purity can be easily extracted from natural gas,and the steam reforming reaction technology of methane has been mature,which makes the research of combined power generation equipment of methane based SOFC,GT and ICE has important practical significance.SOFC-GT combined system is suitable for high-power places,and there are many additional heat exchangers,turbochargers and other equipment,and the use cost is high.Therefore,SOFC-ICE system has its unique advantages in distributed power generation scenarios where the user needs less power and the power changes quickly..This paper takes the SOFC-ICE system as the research object,establishes the thermal dynamic model with the reformer as the core,and designs the power distribution strategy of ICE and SOFC simultaneous power generation based on the system model,and achieves better fuel economy on the premise of completing the power tracking of user dynamic demand.The specific research work is as follows:Firstly,the mathematical description of the main component models of the system is carried out,including the heat exchanger model,the methane steam reforming model of two external reformers,the SOFC and ICE electric power models.Among them,the reformer uses the waste heat of the exhaust gas of the internal combustion engine to carry out the steam reforming reaction,and the other uses the thermal energy of the SOFC anode tail gas to carry out the reforming reaction.Secondly,the thermodynamic model of the fuel passage of the system is established in MATLAB/Simulink.And the change trend of SOFC and ICE power output is analyzed under the condition of fuel temperature change.On this basis,the response performance of the system to the static demand power is analyzed,the rapidity of the reformer temperature change and the power output capability of the SOFC are analyzed,and the fuel economy of the system is evaluated on this basis.Then,in order to make the SOFC enter the working state quickly,the cold start process of the SOFC stack under low temperature conditions is considered,thereby reducing the excessive dependence of the system on the external reformer and improving the dynamic performance of the system.At the same time,in order to improve the fuel utilization rate during the cold start of SOFC,the power of the system energy source is optimized in real time based on the Equivalent Consumption Minimum Strategy（ECMS）.Finally,the performance of tracking user dynamic system power,system thermal dynamics,system fuel economy and other performances after SOFC cold start of the system is analyzed.The simulation results show that cold start can effectively utilize SOFC anode tail gas for fast steam reforming reaction through reformer,optimize the thermal dynamic cycle of the system,and obtain better fuel economy.