Research On Power Flow Calculation Of Hybrid AC/DC Microgrid

In order to realize the efficient utilization of new energy and the convenience of AC/DC load power supply,AC/DC hybrid microgrid is widely used.Power flow calculation is not only a tool for operation state analysis of AC/DC hybrid microgrid,but also the basis for control mode and operation mode adjustment of AC/DC hybrid microgrid.It is a research direction concerned by the power industry to find the power flow calculation method of AC/DC hybrid microgrid with strong convergence and fast calculation speed.Therefore,based on the generalized Tellegen theorem and the uniform iterative format,this thesis studies the power flow calculation of AC/DC hybrid microgrid with theoretical significance and application value.In order to solve the problem that the uniform iterative format needs to calculate the value of all elements in the Jacobi matrix during each iteration,and the huge amount of calculation seriously affects the solution speed of power flow,this thesis presents a current injection model based on the uniform iterative format.In this model,power injection is replaced by current injection on the basis of the unified solution method.The current injection model obtained after the replacement only needs to solve a small number of diagonal element values during each iteration to obtain a new Jacobi matrix.Compared with the power injection model,the calculation amount of Jacobi matrix in each iteration is reduced.This thesis presents an AC/DC hybrid microgrid power flow calculation method based on generalized Tellegen theorem.The small perturbation theorem of the generalized Tellegen theorem is applicable to the current injection flow equation established in this thesis.When solving the power flow equation by using the small perturbation theorem,the specific expression of the adjoint equation can be obtained by only calculating the first order factor table of the Jacobi matrix.In the subsequent power flow calculation,the modified equation can be solved only after solving the unbalance of the injected current and the difference value of the Jacobi matrix.Therefore,the calculation amount of the modified equation can be reduced and the solving time of the power flow can be shortened by applying the method in this thesis.MATLAB was used to simulate the IEEE9 nodes system and 22 nodes AC/DC hybrid microgrid system of China Electric Power Research Institute.The calculation results and time of power flow are compared between the proposed method and the unified method.The results show that the proposed method can improve the power flow solving speed of AC/DC hybrid microgrid under the premise of ensuring convergence.