Research On Global Optimal Control Of District Heating System

Energy conservation and emission reduction is the general trend,and the most potential energy conservation is building energy conservation.In China,the energy consumption of central heating industry is huge and the heating efficiency is low.The energy consumption of its average building area is up to three times of that of developed countries,so the energy saving potential is huge.Therefore,it is necessary to conduct optimization research on the central heating system.Firstly,the control scheme is optimized for problems such as poor heating quality.Then,by taking advantage of the difference between peak and valley electricity prices,an energy storage device is added to the system,which can not only give full play to its energy saving potential,but also play the role of peak and valley filling.In this paper,a mathematical model of district central heating system is established based on the basic principles of heat transfer and energy conservation.The mathematical model of electric boiler is established by means of particle method.The mathematical model of water storage tank is established under reasonable assumptions.By analyzing the fluid energy in plate heat exchanger,a simplified mathematical model is established.Based on the existing data and model understanding,a second order delay housing model is derived which is only related to the water supply temperature and the ambient temperature.The results of model verification show that the established system model can track the system dynamics well.Then,based on the system model,a double closed-loop PI control structure based on Smith forecaster is designed.Firstly,the characteristics of the original hysteresis control scheme are analyzed.The double closed-loop PI control structure is designed without considering the time delay.Secondly,the paper introduces the time-delay link and analyzes the influence of the time-delay link on the system stability,then compensates the time-delay link with the Smith predictor,and simulates the compensation effect of the Smith predictor,and finally designs a double closed-loop controller based on the Smith predictor.Simulink is used to build different control models and analyze different control schemes.Finally,considering only the steady state of the system and ignoring the transient characteristics,the energy storage optimization scheme based on the multi-population genetic algorithm is designed.Firstly,the energy consumption demand model of the house is reasonably equivalent to the heat flow of the secondary side of the plate heat exchanger which is only related to the ambient temperature.Secondly,the genetic algorithm is introduced.Considering the limitation of the genetic algorithm in the large-scale solution space search,the multi-population genetic algorithm is adopted.In the implementation of the algorithm,the corresponding mathematical description of energy storage optimization is given,and then the system constraints in energy storage optimization are described.Finally,the energy storage optimization scheme of multi-population genetic algorithm is designed,and the optimization results are analyzed.