Fault Characteristics Analysis And Pilot Protection Of Distributed Generation Connected To Distribution Network

The consumption of fossil energy will lead to a series of environmental problems,which is not conducive to the sustainable development of human beings.As a clean and sustainable alternative energy,distributed power has developed rapidly.The DG such as wind and photovoltaic power generation access distribution network will affect the current protection of the traditional distribution network,may make the node voltage limit.Therefore,a pilot protection scheme and a voltage control strategy are proposed based the synchronous phasor measurement device.This paper first compares the calculation methods of short circuit current:IEC method,ANSI method,national standard method and DIgSILENT software method(complete method),analyzes the difference between calculation conditions and calculation principle,and then simulates and compares the calculation results of different methods.The selection of short-circuit current should consider the engineering requirements,the applicable scope of each standard and the actual situation of the network.In order to study the output characteristics of the inverter DG in the power grid failure,a voltage controlled current source model for low voltage crossing is built in this paper,which is based on the relationship between the photovoltaic output current and the network voltage control.The accuracy of the equivalent model is verified by the comparison of the equivalent model and the output current of the detailed model when the symmetry fault occurs in the grid and the voltage drop of the network.At the same time,the time of the simulation is also reduced because the equivalent model reduces the integral and differential operation.The equivalent model has a positive significance for the research of subsequent inverter DG control and distribution network protection.Micro PMU relies on high-speed communication network.It has high simultaneity and high accuracy when measuring phasors.In view of the problem of misoperation and rejection of the original current protection caused by DG access to the distribution network,a longitudinal protection scheme based on the current phase comparison is proposed in this paper.The simulation is carried out under three types of fault types(AG,ABG,ABCG).The results show that the scheme can effectively distinguish the fault in the line section and out of the section under the different running state of the distribution network.In view of the voltage limit caused by DG access,this paper puts forward a control strategy to regulate the voltage of the power grid by using the photovoltaic inverter and the load voltage transformer in combination with the voltage information measured by the micro PMU measurement.The simulation results show that the scheme can effectively solve the voltage overvoltage problem caused by high permeability PV access.