## 1 Introduction  
Energy lays the foundation for human existence. It is also the source for social and economic development. In recent years, there has been increasing conflict between energy supply and energy demand, as well as rising environmental concerns. New technologies are urgently needed to improve energy efficiency while ensuring an effective clean energy supply [1]. With the construction of today's energy Internet, there is also a demand of synergistic multi-energy (power, gas, and heat) supply systems to replace the independent operation modes of the traditional energy supply system. The multi-energy microgrid, which is a key node in the energy Internet, has become a popular research subject due to its flexible operation modes and effective energy use forms. New planning and reliability evaluation methods for integrated energy systems are important in this regard. Reference [2] includes the first energy hub model, conceptually illustrating the multi-energy microgrid. This model reflects the complicated relationship of the energy hub from the perspective of energy flow via an energy conversion matrix, and delineates the relations between each energy subsystem in the hub. Reference [3] further expanded the integrated energy system concept and analyzed the characteristics of such systems per the coupling components and synergy of different energy vectors. The emergence of the electric microgrid concept [4; 5; 6] has brought about new multi-energy microgrids with flexible operation modes, having evolved from the traditional distributed energy supply and storage systems. These new systems can ensure the effective accommodation of renewable energy with the mutual support of utility energy grids. The continuous development of microgrid technology will make multi-energy microgrid become an important node of the energy Internet and an effective comprehensive energy utilization model. An accurate reliability evaluation is the basis of any effective planning scheme. The strengthening of coupling characteristics between multi-energy systems affects the reliability of the energy supply. Due to the coupling between energy carriers, there are multiple energy supply points on the demand side, which enhances the reliability of the energy supply. However, as energy supply systems couple with each other, a fault in any one system affects the entire system. Previous researchers have explored various reliability evaluation methods. Analytical and simulation methods [7; 8] are commonly employed to power systems, and may also apply to the assessment of microgrid reliability [9; 10]. However, there has been relatively little research on integrated energy supply reliability evaluation. Some references have extended the range of reliability assessment by adding distributed generation to traditional distribution networks. Here are the examples. Reference [11] employed scenario reduction techniques to assess uncertainties in distributed generation and load in distribution networks; it also explored various strategies to protect against failure in the distributed network. References [12; 13] evaluated the reliability of active distribution networks through analytic and simulation methods, respectively. Reference [12] analyzed the energy hub operation mode and built mathematical models for reliability evaluation that apply to different respective operation strategies. Reference [13] developed a two-hierarchy smart agent model to evaluate active distribution network reliability with Monte Carlo simulations. On that basis, some references further integrated various energy carriers and proposed some static reliability evaluation methods. References [14; 15] built a state space for energy transmission by analyzing the connection between different energies in multi-energy network hubs. They also performed static reliability evaluation of the systems mathematically. Reference [16] built a state model of power grid and gas network components and a reliability evaluation model of an integrated system via the Monte Carlo simulation method.