###### Abstract
This is because each part of the floating nuclear power plant adopts the radial network, and the number of branches and nodes is large. Thus, the condition number of the network Jacobian matrix is large, and the calculation process is difficult to converge. In addition, the R/X value of the line is relatively high, which does not meet the conditions of PQ decomposition, and fast decomposition is not applicable. To solve the above problems, the forward-backward method [18], DistFlow [19], bus impedance [20] and other methods are proposed for the power analysis of shipboard power systems that can quickly calculate power flow. However, for the floating nuclear power plant, when there is an out-of-power generator, other generators are needed to realize power transfer. To ensure the operation efficiency of the generators, the power output among the generators should be distributed based on the rated capacity. Therefore, power output and distribution must be calculated by optimal power flow management. This increases the complexity of power flow analysis, which cannot be achieved by existing methods. The methods of solving network topology reconstruction after power system failure mainly include multi-agent systems [21; 22], the heuristic method [23] and intelligent optimization algorithm [24; 25]. Among these, intelligent optimization has a high search efficiency and can solve the algorithm nonconvergence problem in a high-dimensional system. It is widely used in power system network reconstruction. Intelligent optimization methods mainly include genetic [26] and particle swarm optimization [27] algorithms. The above method is simple in operation and requires few parameters to be adjusted, so the optimal solution can be quickly searched for. However, the search algorithm based on a single evolutionary population cannot achieve cooperative optimization among the search populations, and the results are often only locally optimal solutions [28]. This paper presents a Petri net-based power supply recovery method for the electric power system of a floating nuclear power plant. Based on the structural characteristics, a two-stage power supply recovery strategy is adopted. Emergency power sources are put into the system immediately after fault to prevent power loss to important loads. In the next stage, the whole network reconstruction is realized, and the loss-of-power region is switched to be powered by the main generator. In the process of network reconstruction, the goal is to maximize the total power supply recovery after considering the load weight, to minimize the total switching operating cost after considering the difference between the switches and to maximize the generator operation efficiency. To realize the efficient interaction between the system topology analysis and power flow analysis, the Petri net is used to model the topological structure. The power flow analysis is constructed by simulating the dynamic transferring of the token with the firing of transition in the Petri net model, which is suitable for the compact power system of the floating nuclear power plant. MPGA is used to search for the optimal solution, for which global search and local search are both considered for finding the optimal solution. MATLAB simulation results show that the proposed method can provide complete power supply recovery.