Study On Power Flow And Optimal Power Flow Of Combined Electro-thermal System

The heat network uses steam(or hot water)as a medium to carry out energy transfer through a heating pipe network.Industrial waste heat,renewable clean energy,electricity,fossil fuels and cogeneration sources can be used as heat source.When the thermoelectric unit and electric boiler are the heat source,the thermal system and the power system are thus coupled into a more complex electric heating system.Compared with the independent optimization of the thermal system and the power system,the electro-thermal joint optimization can make the joint system run in the optimal economic stability by adjusting all the control means available in the system.First of all,according to the current situation of the existing heating network model,after comparing the topology and operation characteristics of the actual heating network and distribution network,this paper proposed that the heating network model should be established with reference to the distribution network rather than the transmission network.After a detailed analysis of the difference between the heating network and the distribution network,this paper established a heat transfer model which had taken into account the heat loss of the return pipe network.The model not only overcomes the problem that the heat pipe traditional model can not take into account the heat loss of the return pipe network but also can easily handle the multi-branch radial heat network with energy conversion devices such as electric boilers and thermoelectric units.Secondly,this paper compared and analyzed the operation of the heating network.Based on the most commonly used qualitative adjustment method,this paper present a method of calculating the forward power of the heating network.The method didn't need to solve the hydraulic model,no complicated network number,and no admittance matrix.It has the characteristics of simple programming and fast calculation.In this paper,the calculation model of electro-thermal coupling device and the power flow model of combined electro-thermal system were established,and the sequential calculation method of the combined electro-thermal system was also proposed.Through the numerical simulation,this paper analyzed the influence of the installation location of the electric boiler and the operating parameters of the heating network on the power flow distribution and the wind power consumption of the combined electro-thermal system,and proved that the heat loss of the return pipe network is very large and can not be neglected in the calculation.Finally,based on the above-mentioned heat transfer model and electro-thermal coupling device calculation model,this paper established the operation constraint condition of thermodynamic system and electro-thermal coupling equipment.Combined with the operating conditions of the power system,the optimal power flow model of the electro-thermal system with multi-branch radial heat network was established.In this paper,the interior point method was used to solve the calculation method and the calculation process of the model.Through the comparison of the example and the comparison with the ordinary power flow,it was shown that the optimal power flow can optimize the selection parameters of the heating network in the upper and lower limits of the heat source parameters and optimize the generator output.Therefore,the combined electro-thermal system is more economical in the optimal power flow.