Research On Fault Current Characte-Ristics And Outgoing Line Protection Of Inverter-Interfaced Renewable Energy Resources Grid-Connected System

Since the continuous improvement of the permeability of renewable energy power supply,the influence of new short-circuit characteristics on relay protection becomes more and more prominent.This paper mainly studies the short-circuit current characteristics of power system with inverter-interfaced renewable energy resources and designs the corresponding relay protection scheme.Firstly,the topology of renewable energy resources grid-connected system and the control strategy of three-phase voltage source inverter are introduced.By referring to the requirements of low voltage ride-through and reactive power output in the grid-connection guidelines,fault response process of this kind of system is described.According to the process,the output characteristics of the renewable energy equipment are analyzed,and the influence of fault response on the effectiveness of traditional protection scheme is discussed.Secondly,according to the fault response process of grid-connected system,the output fault current characteristics of the inverter under different control modes are analyzed.The generating mechanism of each harmonic current component in fault current is analyzed,and the transient harmonic characteristics are obtained.The fault information contained in the characteristics can provide effective fault identification,based on which the harmonic trajectory is defined as the characteristic quantity of fault detection.Then,based on the harmonic trajectory characteristics of renewable energy resources grid-connected system,a new protection principle suitable for the outgoing line is proposed.In order to improve the anti-disturbance performance of the protection,fault response link of the line protection is designed by using recurrent neural network.Synthesizing the above two parts,a differential protection scheme based on harmonic trajectory and recurrent neural network algorithm is presented.Finally,the hardware-in-loop simulation experiment model of the grid-connected system was built in real time digital simulator.The performance of the differential protection scheme have been test under different operating condition,such as different fault types,transition impedance,fault points,reliability of the scheme was verified.