Probabilistic Load Flow Calculation For Hybrid Grids Considering Wind-Photovoltaic-Load Dependence

With the proposal of “carbon peaking and carbon neutrality” goals,the multi-terminal DC system based on voltage source converter is widely used in the grid connection of large new energy bases.The output of renewable energy,such as wind power and photovoltaic,is highly uncertain.At the same time,there are a large number of fluctuating power loads in AC power grid,which poses a challenge to the stable operation of AC/DC hybrid power system.In order to better guide the planning and development of the new energy base of the transmission terminal and the coordination and interaction of the AC/DC power grid,and further reveal the influence of wind,photovoltaic and load charged power characteristics on the hybrid system,this paper focuses on the probabilistic tide calculation of the hybrid grid with correlation between wind speed,light intensity and load.In terms of the uncertainty of wind,photovoltaic and load,the paper combines an improved fuzzy C-mean algorithm and a fractional-order maximum entropy model to propose a modeling method for this uncertainty.Fuzzy C-means algorithm was used to cluster the historical data of wind,photovoltaic and load,the scene division scheme is optimized according to the improved Xie-Beni index.Based on the theoretical probability density mathematical model,the relative entropy minimization is taken as the goal,and the fractional moment is established in turn as the constraint to solve the probability density function of wind,photovoltaic and load.By comparing the simulation results of three probabilistic models,it is shown that the fractional maximum entropy model established in this paper can describe the uncertainty of wind,photovoltaic and load better and improve the accuracy of probabilistic modeling.In terms of the correlation of wind,photovoltaic and load,a mixed vine Copula model of wind,photovoltaic and load charge is established by combining Copula theory and vine structure model.A variety of Copula functions were used to fit the correlation between wind,photovoltaic and load,the optimal Copula function type was determined according to Euclidean distance index.C-vine structure and D-vine structure were used to model the correlation between different scenes,and the optimal vine model was determined based on the calculation results of Anderson-Darling distance,and the load mixed vine Copula model was established.By comparing the simulation results of the single vine Copula model and the wind,photovoltaic and load mixed vine Copula model,the simulation results show that the wind-photovoltaic-load mixed vine Copula model can describe the complex correlation of wind-photovoltaic-load in detail and comprehensively,and effectively improve the accuracy of the correlation modeling.In terms of probabilistic load flow calculation of AC/DC hybrid grid,a probabilistic load flow calculation method for hybrid power grids is proposed based on refined modeling of wind,photovoltaic and load.A deterministic power flow calculation model for hybrid power grid was established by combining the voltage source converter model with the DC power grid model.According to the simulation data generated by the wind-photovoltaic-load mixed vine Copula model,the input random variable samples were obtained by Latin hypercube sampling method.The numerical results show that the proposed method can not only give consideration to the accuracy and efficiency of probabilistic load flow calculation,but also flexibly obtain the probabilistic information of input random variables,which has good application value in engineering.