## 2 Developmental Overview  
The concept of achieving energy interconnection through digital technology was first proposed by the American scholar [PERSON] in his seminal work _The Third Industrial Revolution_[10; 11]. This idea has since captured the attention of governments worldwide. For instance, as early as 2002, Switzerland launched the VoFEN project to explore multi-energy transmission systems and the conversion and storage of distributed energy, aiming to develop ideal energy system facilities by 2050. Similarly, the German government initiated the E-Energy program in 2008 and the SINTEG program in 2016, focusing on the goals of low-carbon transitions and nuclear phase-outs. The U.S. government launched the FREEDM project in 2008, which employs advanced power electronics, information technology, and energy management technology to build future renewable energy transmission and management systems. In 2011, Japan formulated the \"Digital Grid\" strategic plan, researching technologies that could be used to integrate power routers with existing power grids and local networks to achieve a deep integration of energy and information networks. In 2016, China's National Development and Reform Commission and National Energy Administration published the \"Guiding Opinions on Promoting the Development of \"Internet Plus' Smart Energy\", emphasizing the necessity of building a green, low-carbon, safe, and efficient modern energy system [12]. The goal is to promote the deep integration of energy and information, accelerate the digitalization and intelligent upgrade of the energy industry, and establish smart energy demonstration projects. By 2025, the initial construction of the energy interconnection industry system is expected to be complete, forming a relatively comprehensive technical and standard system that promotes international and leads global energy interconnection development [13; 14]. Table 1 shows that multiple countries regard the application of energy interconnection industries as a national issue. The energy interconnection system, a novel type of energy system, serves as the physical carrier for realizing \"Internet Plus Smart Energy\". It is the inevitable result of the deep integration of information and energy systems and the reconfiguration and optimization of systems once information becomes a new type of production factor. Countries around the world adopt slightly different technological pathways based on their own energy endowments and technological strengths. Existing concepts can be classified into three categories:  
1. Global Electricity Interconnection Focus: This involves the spatial expansion of power networks by interconnecting different regional power grids to facilitate the cross-regional absorption of various types of new energy sources. 2. Multiple Energy Sources Coupling Focus: This involves interconnecting various energy systems, including electricity, heat, cold, gas, and water, to enhance comprehensive energy development and utilization and improve energy efficiency. Here, electricity is converted into different forms of energy such as cold, heat, and gas to harness renewable energy sources. 3. Energy-Information Integration Focus: This primarily utilizes technologies such as power electronics, information communication, and the internet for energy control and real-time information sharing, aiming to achieve energy supply-demand matching. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**National** & **Project** & **Time** & **Focus** & **Interconnection Type** & **Features** \\ \hline \multirow{8}{*}{Sweeden} & \multirow{8}{*}{VoFEN} & \multirow{8}{*}{2002} & \multirow{8}{*}{Focus on the comprehensive interconnection of various energy sources} & \multirow{8}{*}{Physical interconnection} & \multirow{8}{*}{Transportation, on one hand, to achieve the transmission, conversion, and efficient utilization of various energy sources, and, on the other hand, to convert surplus electricity into other energy sources to complement, accommodate, and store electrical energy.