## 1 Introduction  
In recent years, with the increasingly obvious shortcomings of traditional energy and the rapid development of new energy technologies, [PERSON], an American economist, first put forward the concept of Energy internet in 2011 [1]. The concept focuses on replacing traditional energy with clean renewable energy so that we can reduce the proportion of traditional energy in industrial development and combines internet technology to realize interconnection, interoperability, and complementarity of current energy resources, which will maximize the efficiency of energy utilization. The energy network, which integrates new energy technology and information technology, has become the future direction of energy development [2, 3]. With the construction of the Energy internet, the power system coordinated optimization mode of \"source-network-load-storage\" has become the core link of the development of Energy internet. This mode can be more widely applied to the whole energy industry and combine the technology and operation mode of Energy internet to form a coordinated and optimized operation mode of the whole energy system, as shown in Figure 1[4]. Under this model, as a mature form of integrated energy network, electric-gas combined system (EGCS) has different ways and principles of coupling between the two networks, and their relationship is becoming closer. Recently, the study on EGCS is mainly manifested in power flow modeling, dispatching optimization, and security issues. 1. How to model EGCS? [PERSON] et al. established a mathematical model to evaluate the maximum power supply capability of EGCS from the perspective of the influence of the natural gas network on the power supply capability [5]. Under the premise of considering the gas pipeline constraints in the natural gas network, [PERSON] et al. analyzed the degree of interaction between the electric-gas networks by simulation from the perspective of security, and the electric-gas joint risk assessment model is established [6]. Based on the economics, [PERSON] et al. analyzed the multi-stage planning problem of EGCS through economic optimal model simulation [7; 8]. 2. Calculate the power flow of EGCS. Because of the coupling between different energy forms in the EGCS, the traditional models and mechanisms for solving a pure power system or natural gas system are no longer suitable for solving the mixed power flow of EGCS. [PERSON] et al. firstly proposed that natural gas network be modeled by analogy to the grid, and then solved the gas network power flow by using the grid power flow calculation method [9]. [PERSON] et al. analyzed the power flow model in EGCS and studied the difference between mixed power flow and single power flow [10]; [PERSON] et al. considered the calculation error problem caused by the uncertainty factors in the system, and solved the flow problem of EGCS by introducing the concept of probabilistic flow [11]. 3. There is a non-negligible uncertainty problem in EGCS [12; 13; 14; 15]. From the perspective of energy output or utilization, the uncertainty can be distinguished as energy output side uncertainty and energy demand side uncertainty. The access of distributed energy (DG) will greatly increase  
Figure 1: Coordination and optimization operation mode of “source-network-load-storage” of Energy internet. the degree of uncertainty. [PERSON] et al. analyzed the influence of uncertainty degree of energy output or response on the economy or market mechanism of EGCS [16; 17]. [PERSON] et al. provided a model description of the demand-side response of the system or the uncertainty of DG and formulates the operation strategy of EGCS by adding constraints involving uncertainty [18; 19]. 4. Study the dispatching operation strategy of EGCS. Grid and the natural gas network are two kinds of networks with different energy sources. When they are coupled, the formulation of dispatching and operation strategy is different from that of a single network. [PERSON] et al.