Research On Power Flow And Optimal Power Flow Of Integrated Energy System Based On Energy-circuit Theory

The integrated energy system contains a variety of heterogeneous energy networks,such as electricity,heat,cold,gas and so on.Multiple energy flows interact with each other through coupling devices,which is conducive to promoting the complementary substitution and cascade utilization of energy,and is of great significance to improving the utilization rate of integrated energy.In the traditional energy flow analysis,the modeling methods and analysis ideas of electricity,heat and gas networks are different,so it is difficult to analyze the coupling of heterogeneous energy networks in essence.In this thesis,based on the unified energy-circuit theory,the equivalent model of gas network with compressor is proposed,and the combined water-heat model of heating network is deduced.On this basis,the multi-energy flow calculation and optimal multi-energy flow problem of integrated energy system are studied.Firstly,the unified energy-circuit model of integrated energy system is established.Based on the energy-circuit theory,the natural gas system model is established,and the equivalent calculation model of gas network with compressor is proposed,which is helpful to reduce the computational complexity.Based on the energy-circuit model of thermal system,considering the coupling of hydraulic and thermal power,and referring to the power flow calculation of electricity system,a combined water-heat model of heating network expressed by node thermal power is proposed.The coupling link models are established,including thermal power unit,gas unit,gas steam combined cycle unit,electric boiler and power to gas device.Secondly,the multi-energy flow calculation method of integrated energy system based on energy-circuit theory is studied.In this thesis,the simultaneous calculation method of multi-energy flow suitable for strong coupling system is used.The simultaneous calculation model of electric-gas-heat integrated energy system is established.And its Jacobian matrix element calculation formula is derived.In order to improve the convergence of the unified iteration of multi-energy flow and reduce the amount of calculation,the selection of reference value and the calculation method of standard unit value for natural gas and thermal system are proposed.The simulation results show that the model and method are effective and fast.Further analysis shows that the water supply of heat source affects the node pressure and heat loss of heating network.The larger the water supply,the lower the node pressure and the smaller the heat loss.It is verified that the proposed model is sensitive to load fluctuation and can calculate the power flow of heating network effectively.Finally,the optimal multi-energy flow of the integrated energy system is calculated based on the energy-circuit theory.Taking the minimum system operation cost as the objective function and considering the operation constraints of power grid,gas network,heat network and coupling equipments,the optimal multi-energy flow model of electric-gas-heat integrated energy system based on energy-circuit theory is established.The interior point method is used to solve the model.The simulation results show that the optimal multi-energy flow has better economic benefits than the ordinary multi-energy flow.The lower the water temperature of the heat source connected to the condensing unit,the better the system economy.The operating cost of gas-fired units is higher than coal-fired units.The smaller the output of gas-fired units,the lower the operating cost of the system.In this thesis,the modeling,power flow and optimal power flow of electricity-gas-heat integrated energy system are studied comprehensively.It deepens the unified analysis of heterogeneous energy flows and provides an effective steady-state analysis method for the system,which is of great significance to its economic operation.