Power Flow Optimization Of AC/DC Hybrid Distribution Network Based On Unified Branch Model

With the increasingly prominent environmental and energy issues,sustainable low-carbon energy has gradually received attention and development,and it is necessary to actively develop clean energy to meet the needs of environmental protection and energy demand.Therefore,China has proposed a great vision of building a new type of power system dominated by new energy.With its advantages of large reserves and wide distribution,photovoltaic has achieved rapid development in China.Nowadays,the development of power electronics technology,the increase in load ratio,and DC power sources have led to the transition from traditional AC distribution networks to AC/DC hybrid distribution networks.The grid connection of renewable energy,load fluctuations,and the access of large-scale power electronics converters have made power flow calculation difficult.Power flow calculation is the most fundamental research of AC/DC hybrid distribution network systems,and can be used for stability analysis,reliability analysis,potential risk analysis,and other aspects of system operation.Aiming at the problem that power flow modeling for AC/DC hybrid distribution networks cannot accurately characterize arbitrary topologies,has scenario limitations,and does not include multiple DC voltage levels,this paper conducts research on power flow calculation for AC/DC hybrid distribution networks based on branch models;at the same time,in order to reduce the impact of random and volatile photovoltaic and load grid connection on the system,this paper optimizes the power flow of complex AC/DC hybrid distribution systems considering source load uncertainty to ensure safe and stable operation of the system.The main research content of this article is as follows:Firstly,conduct steady-state modeling of power electronic converters.By analyzing the steady-state characteristics of voltage source converters(VSCs),establish steady-state models of VSCs under different control strategies.At the same time,simulate the treatment methods of dual winding transformers in traditional AC distribution networks,and establish steady-state models under different control strategies for DC/DC converters with different topologies.Secondly,a unified branch model based power flow calculation for AC/DC hybrid distribution networks is proposed,and a branch power flow model for possible connection schemes between arbitrary nodes of AC/DC hybrid distribution networks in different scenarios is established.On this basis,a unified branch power balance equation for AC/DC hybrid distribution networks is established by expanding the definition of the network matrix.Through Jacobian matrix modification,a unified iterative power flow solution algorithm based on Newton Raphson method for AC/DC hybrid distribution networks considering different converter control strategies is proposed,and the accuracy and robustness of the proposed model and algorithm are verified in different computational scenarios.Finally,a power flow optimization method for AC/DC hybrid distribution networks considering source load uncertainty based on the Non dominated Sorting Genetic Algorithm-Ⅱ(NSGA-Ⅱ)with elite strategy is proposed.A multi-objective optimization model considering system economy and reliability is established,which considers minimum network loss and minimum system voltage offset.The model is solved using the NSGA-Ⅱ algorithm,and the optimal compromise solution is obtained from the Pareto solution set using maximum satisfaction.The method and process for solving the model are discussed in detail.In order to study the impact of the randomness and volatility of photovoltaic and load on the system,numerical examples under different scenarios were used to analyze and verify the correctness and effectiveness of the proposed model and algorithm.