Research On Operation Optimization Of Flexible Interconnected Areas With High Proportion Of Household Photovoltaic

Driven by both national policies and energy development,the number of household PVs connected to the grid in the station area is growing explosively.After the large-scale household PVs is connected to the grid,the excess active power of PVs will lead to the deterioration of the operating environment of the station area,and the problems of voltage fluctuation and limit crossing,three-phase imbalance and network loss will be more prominent.The traditional distribution station is a single radial structure,with a single means of regulation and control,and lacks power support,which makes it difficult to meet the grid-connected demand of large-scale household PVs.Considering that the flexible interconnection AC-DC hybrid power supply and distribution form has more powerful tidal control ability and distributed power local consumption ability,it is one of the important means to effectively cope with the above problems.In this paper,we focus on the study of low-voltage flexible interconnection technology in the operating environment of station area with high proportion of household PVs,as follows:(1)A model of the relevant components of the flexibly interconnected station area and an operational steady-state model are established.The component models include the models of household photovoltaic power generation units,energy storage devices and flexible interconnection devices,and the steady-state models of the station area include the line model of the three-phase four-wire low-voltage distribution network,the three-phase tidal model based on the current injection Newton method and the tidal model of the DC system based on the Newton-Raphson method,which is verified by a flexible interconnected low-voltage distribution network with double-ended FID.(2)Considering the integrated access of flexible interconnection device and energy storage device,a flexible interconnection-based AC-DC hybrid low-voltage station area supply and distribution form is proposed.On the basis of constructing the integrated access model of FID and energy storage based on B2B-VSC,an operation optimization strategy considering the voltage crossing limit,three-phase unbalance and high network loss in the station area is designed,and the optimization model is simplified by using the idea of second-order cone relaxation and linearization,and the FID second-order cone constraint is fitted by using positive sixteen deformation to reduce the difficulty of model solving.The improvement of the operating environment of AC station area is analyzed from multiple perspectives of FID DCside energy storage access influence and optimization weight coefficients.The results show that the proposed AC-DC hybrid supply and distribution model based on flexible interconnection within the station area can effectively improve the regulation capability of the station area and improve the power quality level of the station area carrying distributed energy.(3)A station area power supply pattern with flexible interconnection at the end of AC station area and low-voltage DC system is adopted,and a two-stage hybrid ACDC optimization scheme with multiple complementary devices considering on-load regulator,shunt capacitor bank,VSC and energy storage is designed.In the first stage,the optimal 24 h operation sequence of OLTC and shunt capacitor bank is obtained with PVs consumption and network loss reduction as the objective function;in the second stage,the short-time power characteristics of PVs and load are considered and the results of the first stage are combined to optimize the short-time power output of VSC and energy storage devices with PVs consumption,network loss reduction and node voltage deviation as the objectives.Based on the second-order cone relaxation and linearization,a k-meas clustering-based dynamic decoupling strategy is used to decouple the variables in the optimization model for continuous optimization that cannot fully model the discrete variables.The results of the algorithm show that the proposed method can effectively improve the AC station operation and enhance the station PVs consumption capacity.