## 1 Introduction  
With the increasingly prominent energy crisis, environmental degradation and other problems, distributed generation (DG) as an environmentally friendly, efficient and flexible form of power generation has been widely investigated and developed. Due to its inflexible structure and limited regulation means, the traditional distribution network cannot effectively suppress the uneven distribution of power flow brought by the access of DG, and the over-limit of feeder voltage, which limits the consumption capacity of DG in the distribution network [1; 2; 3]. At present, there are two kinds of research methods on how to improve the consumption capacity of DG in the distribution network. One is to improve the consumption of DG by using the regulation method in the traditional distribution network. Some studies [4; 5; 6] introduced the distribution network reconstruction method oriented to the consumption of DG to obtain the optimal distribution network reconfiguration results and DG output scheme. However, the reconfiguration of the distribution network is completed by the opening and closing of the contact switch. In the actual operation process, there are problems, such as the delay of switching operations and the impact of the closing ring current, which affect the safe and reliable operation of the network. A further study [7] adopted a distributed model for predictive control to optimize and control the controllable DG, energy storage, flexible load and other controllable resources in the region. However, the optimization results depend on the accuracy of the model's prediction and cannot guarantee the actual optimization results. In recent years, with the development of power electronics technology, the use of flexible devices to improve the ability of distribution network to consume DG has become the main research direction. Among them, these studies [8; 9] changed the reactive power flow and adjusted the voltage deviation of the distribution network to increase the output of the distributed power supply by optimizing the configuration mode of the static var compensator (SVC) and static synchronous compensator (STATCOM) respectively. However, these methods can only adjust the distribution of reactive power flows. Therefore, the consumption ability of the distributed power supply needs to be improved. Compared with the traditional power electronic reactive power compensation device mentioned above, a flexible multi-state switching (FMSS) device is featured with decoupling control of the power and reactive power, continuously adjustable power and fast response speed. This is the premise to realize the consumption capacity of DG in an optimized distribution network [10]. However, some studies [11; 12] mainly realized the load transfer and network frame reconstruction between feeders of the distribution network through a soft-normally-open point (SNOP), to improve the consumption capacity of DG in the distribution network. Further studies [13] compared the consuming capacity of the three-terminal SNOP with a two-terminal SNOP for distributed power supply, and concluded that the three-terminal SNOP consumed 20% more distributed energy than the two-terminal SNOP, which verified the superiority of a multi-terminal flexible switch compared to a two-terminal flexible switch. Another study [14] established the flexible distribution of the distributed power maximum access capacity model, the multiple population genetic algorithm to obtain the global optimal solution and analysis, and completed the flexible distribution of DG based on SNOP maximum access capacity calculations. The maximum consumable capacity of a distributed power supply with different SNOP access modes and capacities is analyzed in detail. However, the methods mentioned above all laid particular emphasis on system planning and topological structure change, and focused on how to use FMSS to improve the capacity of the distribution network to consume DG.