Research On Modeling And Control Strategy Of Solar Thermal Power Generation System Based On Petri Net

Compared with photovoltaic power generation,concentrated solar power(CSP)has the advantages of energy storage,night power generation,and continuous and stable power generation.From a technical point of view,it is completely feasible to replace traditional energy generation with CSP.Therefore,there is a great significance and application value in the research on CSP plants.However,China’s solar thermal power generation large-scale production which is in the demonstration stage is still affected by many uncertain factors.This thesis takes the linear Fresnel solar thermal power generation system as the main research object,and establishes the mathematical model of each subsystem through the method of mechanism modeling.According to the logic switching rules of the system under different working conditions,the hybrid system model is established,and then the dynamic operation and temperature control of the solar thermal power generation system are studied and verified by the actual data.First of all,the energy balance model and the empirical formula are used to establish the energy balance model of the vacuum tube compound parabolic collector in the linear Fresnel solar thermal power generation system.The temperature distribution of the heat transfer fluid(HTF)along the radial direction of the collector and the factors affecting the thermal efficiency of the collector are analyzed.Then the mathematical model of the heat storage tank and the steam generator is established to analyze the heat loss of the heat storage subsystem when there is no external heat source and the heat exchange process of the steam generator.In order to prevent the molten salt from solidifying,an additional electric heating device is arranged for the molten salt tank.Secondly,due to the intermittent nature of solar resources and the influence of external weather conditions,the system will be coupled to operate in four modes of freeze protection,preheating the collector field loop,heat storage tank to store heat energy and heat output under load to meet the output demand of steam turbines under different working conditions.Therefore,according to the characteristics of different working modes of CSP,combined with the logic switching criterion of the system,this thesis establishes the extended differential Petri net model of linear Fresnel solar thermal power system.At last,the feasibility and effectiveness of the model is verified by comparing and analyzing the simulation results of Matlab and the calculation results of SAM simulation software.Under typical weather conditions,a simulation analysis was carried out on the energy transfer process of the power station and the coordinated operation process of the pump unit,which provided a theoretical basis for the operation simulation of the linear Fresnel solar thermal power generation system using the molten salt direct heat storage method.Using typical annual radiation data,a preliminary estimate of the thermal performance of the system under annual operating conditions is made.Finally,in order to ensure a stable power output and the temperature of the molten salt outlet of the heat collection loop to maintain a set operating point,this thesis aims at the nonlinearity and complexity of the dynamic model of the heat collection field,and simplifies the dynamic model of the heat collection field.The data of the national solar thermal power generation demonstration project that has been connected to the grid has been collected for experimental verification.The relative error between the simulation calculation result and the actual data is within 0.3%,indicating that the steady-state result of the model is correct and reasonable.Based on the simplified dynamic model,a kind of dynamic matrix controller(DMC)is designed for a large number of random,uncontrollable disturbances in the control process.And the purpose of controlling the stability of the outlet salt temperature is achieved by adjusting the molten salt flow rate.A steady-state Kalman filter is designed to estimate the state variables which aims to further improve the system’s ability to suppress unmeasured interference,so that the system has better stability and robustness.Through simulation experiments,it is concluded that the DMC control system based on Kamlan filtering has more overshoot than the traditional DMC control system,taking into account the solar radiation intensity,ambient temperature,inlet salt temperature,and other unmodeled disturbances.Smaller,better control effect.