| Gas turbine generators and P2G(Power to Gas)devices make it possible for bidirection flow between power system and natural gas system and also make the coupling relationship between the electrical and natural gas interconnected system become more close and complex,this coupling will affect the reliability of the electrical and natural gas interconnected system simultaneously.Thus only the reliability evaluation of single system can not meet the requirements of the multi energy interconnected system,it is necessary to explore the reliability evaluation for multi energy system considering this coupling relationship.Linking natural gas network with electrical distribution network by gas turbine generator and P2 G device can realize the synergistic optimization and complementation of electricity and gas.And the energy storage device can smooth the fluctuation of distributed generation.The energy utilization rate and reliability can be effectively improved by this means.Therefore,this paper takes electrical distribution and natural gas interconnected system as the research object to explore the reliability evaluation model for interconnected system.The main contents of this paper are as followed:(1)Based on the physical characteristics of components in natural gas system,steady gas flow models of pipeline and compressor are established.Then based on the steady flow models of components and the first law of Kirchhoff,the gas flow balance equation of each node is written,and the formula of Jacobi matrix is given to realize the calculation of steady gas flow,which provides the basis for the reliability evaluation of the natural gas system(2)Although the reliability evaluation for power system is perfect,the quantitative reliability evaluation for natural gas system is rare currently.In order to compare the reliability of single natural gas system with electrical distribution network and natural gas interconnected system,it is necessary to evaluate the reliability for natural gas system.Based on the similarity between the natural gas system and composite system,the basic theory of the reliability evaluation for power bulk system are applied to natural gas system,and the reliability evaluation index and the optimal gas load shedding model for the natural gas system are proposed.The sequential Monte Carlo algorithm is used to simulate and analyze the 11-node natural gas system,and the results of the reliability calculation are compared with the analytical method and non sequential Monte Carlo method.The validity of the proposed index and model are verified,which laid the foundation for further studying the reliability evaluation of electrical distribution and natural gas interconnected system.(3)The reliability of electrical distribution and natural gas interconnected system is studied considering the relationship between two systems and the influence of energy storage.The mathematical models of distributed generators,load,gas turbine generator and P2 G device in the interconnected system are built up respectively.The charging and discharging model of battery storage is established based on charge and discharge constraints.According to Bernoulli’s law,a gas charging and discharging model of gas storage tank which considers the maximum charging/discharging rates and gas storage volume constraints is established through a series of mathematical derivation.Then the proper energy storage strategy is proposed to smooth the fluctuation of the distributed power supply in the interconnected system.For the load shedding state,load shedding order of isolated island is decided by the load shedding coefficient and the load shedding of gas is calculated according to the improved gas load shedding model.By comparing the sequential simulation results of the RBTS-BUS6-F4-NGS11 interconnection system,the separate RBTS-BUS6-F4 distribution system and the 11-node natural gas system,the difference between the reliability level of the interconnected system and the single system is analyzed.Finally,it is concluded that the reliability level of the interconnected system will be better than single system and the implementation of distributed generator and energy storage devices will further improve the reliability of the electrical distribution and natural gas interconnected system. |
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