Distance Protection Of Grid-tied Pv Distribution Lines

As the scale of new energy power generation continues to expand,the problem of large-scale centralized new energy grid is becoming more and more serious.Distributed new energy generation,which is closely connected with load and has little impact on the power grid,has received extensive attention in recent years.Distributed photovoltaic power generation relative wind power technology has a better application scenarios,but its trend of change of distribution network and the inverter control strategy,also can bring new problems to traditional sectors such as relay protection.Distance protection and over-current protection is general distribution network protection,short circuit current provided by the photovoltaic(PV)power is limited by the grid inverter,with the current superposition of conventional power supply for the measurement of distance protection and actions have an impact.It is also an urgent problem to study the characteristics and setting methods of distribution network protection including photovoltaic power stations.This thesis deals with the protection of the power lines(distribution feeders)that connect the PV power plants(PVPP)to the grid;it analyses the impact of the GCPV(grid-connected PV)system on the conventional distance protection.In practice,the fault transition resistance generally exists,which misleads the operation of distance protection.Especially for distribution networks with GCPV systems,the measured impedance will be more inaccurate and mislead.A specific coordination between the over-current protection of the grid side and the distance protection of the PVPP side was used to eliminate this impact.This coordination requires delaying the distance protection and keeping the inverter connected to the grid,which was achieved by fault ride-through(FRT)feature accompanied with the inverter control during the fault condition.The simulation was studied using phase to phase(BC)fault at 10 km away from PV side with a 2? fault resistance at 0.8s.Firstly the coordination was done without applying a fault ride-through(FRT)strategy and no voltage and frequency references were available after the OCR isolate the grid side.Then it was tested using FRT and voltage and frequency references.The thesis focused on the ability of protecting the PV power plants distribution lines using the conventional distance protection without changing the coordination of the upstream protection.All the work was verified by a 400 kW grid-tie PV system model using MATLAB/Simulink software.