Research On Feeder Protection Of Microgrid

The microgrid,which is different from the transmission and distribution networks,combines a distributed power supply,load,control and protection to form a single controllable unit.It effectively solves the problems of the limited capacity and quantity when distributed power supply is connected to large power grid.As one of the key technologies of microgrids-relay protection is facing challenges.The traditional three-stage current protection for low voltage distribution network can not adapt to the protection of microgrid with new fault characteristics.So it is urgent to propose new protection methods for the fault characteristics of microgrid.This paper mainly studies the feeder protection problem in microgrid.In this paper,the inverter-based distributed generations in the microgrid are equal to the DC source.The simulation model of microgrid with master-slave control method is established on the PSCAD.The fault characteristics of inverter with constant power control and constant voltage constant frequency control are analyzed and simulated.When the fault occurs in the far distance,the output of the inverter with different control strategies is according to the purpose of control.When the fault occurs in the near distance,the output of the inverter with different control strategies is equivalent to constant current sources.In order to solve the problem that the fault current difference between different operation modes of the microgrid is large and the problem that the action cooperation between the protection is difficult,the current differential protection with cosine quantity is introduced.Its braking coefficient is bigger,the reliability and the sensitivity are higher.And it overcomes the shortcomings of traditional current differential protection which can not simultaneously improve the reliability and sensitivity.In addition,the inverse time low voltage method of converting three-phase instantaneous effective value of voltage,combined with the energy direction components together constitute the microgrid feeder backup protection program.The effectiveness and superiority of the feeder protection scheme proposed in this paper are verified by the simulation experiment of the typical fault points of microgrid.