Analysis Of Fault Component Characteristics And Research On Protection Methods For Distribution Networks With Inverter-based Distributed Generators

With the proposal of the "carbon peak and carbon neutral" strategy,the replacement of coal-based power generation technologies with clean energy-based power generation technologies will become the trend of future power grid development.However,the access of distributed generator(DG)based on renewable energy changes the power flow path and short-circuit current of the power grid.Not only that,the grid-connected DG is mainly inverter-based DG(IBDG),and its output has the characteristics of strong nonlinear,intermittent and fluctuating.Due to the above factors,the traditional fault analysis method and the protection method based on the traditional fault characteristics are no longer suitable for the distribution networks with IBDG.To this end,this paper conducts the following research on the fault analysis and protection methods of distribution networks with IBDG:(1)For the grid-connected IBDG,considering the influence of grid-connection regulations and various control strategies,the relationship between its fault component output current and the positive sequence fault component of voltage at the point of common coupling(PCC)is analyzed.Based on this,an equivalent model of the IBDG fault component current is established.The simulation results based on PSCAD/EMTDC show that the established equivalent model can accurately represent the control strategies and the output characteristics of the IBDG fault component current.Moreover,the output of the IBDG fault component current is highly nonlinear,and its fault component impedance is capacitive.(2)Aiming at the unbalanced distribution networks with IBDG,firstly,the fault component decoupling compensation model of the unbalanced parameters and the fault component equivalent network are established.And fault current of the unbalanced distribution networks with IBDG in the sequence network is deduced.An iterative correction method is proposed to solve the non-linear relationship between the unbalanced parameter fault component compensation current,the IBDG fault component current and the node fault component voltage.On this basis,a fault analysis method based on the fault component network that takes into account the ridethrough time sequences of IBDGs control is proposed,and the characteristics of the fault component voltage and current are analyzed.The simulation results based on PSCAD/EMTDC show that the proposed method can accurately calculate the fault component of unbalanced distribution networks with IBDG,and its physical significance is clear,which lays a theoretical foundation for the research on the principle of fault component protection.(3)In order to adapt to the distribution networks with high penetration T-connected IBDG.Based on the analysis of the effect of T-connection IBDG on the conventional fault component current differential protection,according to the idea of multi-terminal differential protection,an adaptive fault-component-based current differential protection scheme for distribution networks with IBDG is proposed.The proposed method uses the electrical information at both terminals of the protected line to estimate the fault component current of IBDG in the protection range in real time,thereby eliminating the influence of IBDG.The biggest difference with multi-terminal current differential is that the fault component current of IBDG proposed in this paper is obtained by real-time estimation instead of direct measurement.It does not need to install a separate measuring device and communication channel for IBDG,thus has a strong economic.Simulation results show that the proposed protection can adapt to different access capacity and access location of IBDG,and is not affected by fault location,fault types,fault resistance,load and capacitor switching,and can maintain high sensitivity under high penetration.