An Improved Three-phase Power Flow Model And Fuzzy Power Flow Calculations Of Medium-and Low-voltage Distribution System

Distribution system power flow calculation is a basic calculation of distribution system steady-state analysis,and also the foundation of state estimation,fault analysis,network reconfiguration,reliability assessment and other calculation.System power flow calculation have an important position in distribution system planning and operation.Compared with the high-voltage distribution system,the three-phase asymmetry of medium-voltage and low-voltage distribution system is more outstanding.Therefore,the single-phase power flow calculation is not adequate,and three-phase asymmetry power flow calculation is always an important area.The existing studies have not yet adequately considered the network configuration,neutral point operation and their influence on power flow of the integrated medium-and low-voltage distribution system.What's more,with the development of the distributed power generation technology,many distributed sources are connected to the integrated medium-and low-voltage distribution system.How to take the configuration and control features into consideration is becoming a new problem of the integrated medium-and low-voltage distribution system power flow.Meanwhile,there are difficulties in data acquisition of the integrated medium-and low-voltage distribution system.It is a problem of considering the uncertainties in power flow calculation.To this end,this paper does some studies around the power flow calculation and uncertainty analysis of the integrated medium-and low-voltage distribution system power flow.The main contents and achievements are as follows:(1)Taking the line-to-line voltage controllability into consideration,an improved three-phase power flow model for the integrated medium-and low-voltage distribution system is proposed.On the basis of existing research,taking the line-to-line voltage controllability into consideration,an improved slack endpoint model and an improved PV endpoint model are proposed.Moreover,combining the configuration and grounded feature of network,an improved three-phase power flow model for the integrated medium-and low-voltage distribution system is proposed.The IEEE 4-bus test system is used to verify the improved model proposed.(2)An three-phase steady-state model of ungrounded VSI is proposed.Taking the line-to-line voltage controllability and PQ/PV/PI control objective into account,three-phase steady-state models of current/voltage ungrounded VSIs are proposed.What's more,combining the proposed improved power flow model of network,a three-phase power flow model for the integrated medium-and low-voltage distribution system with ungrounded VSI is proposed.The 24-bus test system is used to verify the improved model proposed.(3)An fuzzy power flow calculation method for the integrated medium-and low-voltage distribution system considering load and conductor length uncertainties is proposed.Due to the probability mode of load being acquired more easy,this paper build possibility mode of load from its probability mode,with the possibility/probability consistency principle.Combining the fuzzy mode of line length,the power flow of the integrated medium-and low-voltage distribution system with load and line length uncertainties is calculated by ?-cut arithmetic.Amedium-and low-voltage distribution system of Chongqing is used to verify the method.