Research On Real-time Simulation Technology Of Dynamic Characteristics Of Active Distribution Network

With the increasing penetration of distributed generator,energy storage system,controllable load and micro grid in the power grid,the distribution network is transformed from the traditional passive network into the active network.Its structure will have diverse features,which may be AC/DC hybrid complex distribution network.In order to realize the electromagnetic transient real-time simulation of distribution network with multi class distributed generators,taking the AC/DC flexible distribution network as an example,this paper studies the real time simulation modeling technology and the functions of the AC/DC flexible distribution network.Firstly,the mathematical model of the doubly fed wind power generation system,the direct drive wind power generation system,the photovoltaic power generation system and the energy storing device are introduced,and the adaptability of the distributed power supply in real time simulation is discussed.Secondly,the modeling principle of ideal switching method,ADC method,average value model method and switching function method in two level voltage source converter are expounded,and the adaptability of the above modeling method in real time simulation is discussed.On this basis,a two level VSC switching function modeling method for real-time simulation is proposed and applied to the modeling of the converter in the distributed generation.Thirdly,this paper selects modular multilevel converter as the converter between AC and DC power grid.However,MMC containing a large number of power electronic switching devices will bring great difficulties to real-time simulation.To solve this problem,a MMC modeling method based on ideal transformer model is proposed,which includes the MMC segmentation principle,the error compensation based on interpolation prediction,and the numerical model of the half bridge and full bridge sub module.The simulation results show that the MMC modeling method can greatly shorten simulation time and has a high precision.Finally,an AC/DC flexible distribution system based on MMC is established.Several typical control strategies of the converter are established,and the functions such as uninterruptible power supply,power flow optimization and intermittent energy dispatch are realized.In order to minimize the loss of distribution network,a power flow optimization method based on current moment is presented.