Research On Tidal Current Calculation And Optimal Control Scheme Of AC-DC Hybrid Distribution Network

In recent years,the explosive growth of new DC source loads such as photovoltaic and electric vehicle charging facilities has further increased the peak-to-valley load difference,putting forward higher requirements on the power supply capacity of lowvoltage grids.The existing AC power supply + customer-side AC/DC conversion mode of AC/DC source load is divided from each other,which brings problems such as difficulty in increasing grid capacity,low utilization of power supply equipment and low reliability of power supply,and poses great challenges to the current structure and control mode of distribution network.The AC-DC hybrid distribution network is better than the traditional AC distribution network in terms of tidal current regulation and fault recovery,etc.As the construction process of new power system mainly based on new energy sources in China is accelerating,the traditional AC distribution network is in transition to the AC-DC hybrid distribution network.In this paper,the optimal control of low-voltage AC-DC hybrid distribution network is studied from the following three aspects.(1)For the low-voltage AC-DC hybrid distribution network,the basic model of AC-DC hybrid distribution network is studied.Firstly,the network equipment of ACDC distribution network and the grid structure of the distribution network are analyzed;secondly,the main equipment of AC-DC distribution network including distributed power supply,converter equipment,reserve equipment and multi-port new flexible multi-state switch is modeled and analyzed;finally,the solution method of robust optimization is introduced for the uncertainty of distributed power supply and load in the distribution network.(2)The tide calculation for the hybrid AC-DC distribution network is analyzed.Firstly,various tide calculations for distribution networks are described,including the sequence component method,Gauss-Seidel method,etc.Secondly,an alternating iterative method for AC-DC hybrid distribution network tide calculation and network loss analysis is proposed,and the alternating solution method is selected as the tide calculation method for AC-DC systems according to the established tide model of the converter.The algorithm of DC distribution network tide calculation under master-slave and sag control strategies is given,and a method of AC-DC distribution system tide calculation is designed.Finally,the AC-DC distribution network arithmetic system is used to verify the designed tidal current calculation and network loss analysis methods.(3)Taking minimizing network loss,voltage deviation and operation cost as optimization objectives,this paper proposes a multi-objective robust optimization method based on flexible device interconnection,forming a "deterministic" optimization model with multi-controllable means and multi-objective.On this basis,the two-stage robust optimization model is established by considering the uncertainty;meanwhile,after the model is built.The example shows that the method significantly improves the economy and stability of the system.