Research On The Impact Of MMC-HVDC On Relay Protection In Guangzhou Power Grid

With the development of Guangzhou power grid structure,the capacity and reliability of power supply is gradually increasing,at the same time,the comprehensive influence of the power supply,the continuous production of growth factors such as load level,the short-circuit current level of Guangzhou power grid is a trend of sustained growth,was forced to remove the high and low voltage electromagnetic loop network.Active power using MMC-HVDC system fast independent control of reactive power and transmission capacity,improve the reliability of power supply in Guangzhou,improve the ability of dynamic reactive power compensation,improve the flexibility of power grid operation.But the control method of the coordinated control system of HVDC flexible system is flexible,according to the asymmetrical faults in the AC system the controller can restrain the negative sequence component,change the traditional fault fault characteristics,and impact on traditional protection reliability of the AC line.As a result,the control mode of the flexible HVDC transmission system and the impact on the AC protection in Guangzhou power grid are particularly urgent.Firstly,study on MMC converter topology,working principle and modulation control strategy and other aspects,the basic theory to build a steady-state simulation model of MMC-HVDC system corresponding based on PSCAD/EMTDC.Then,when the AC grid asymmetric faulted,according to the signal delay method,obtain DQ axis positive and negative sequence component of voltage and current,improve extraction of positive sequence component of phase-locked loop,control strategy of mathematical modeling and design of negative sequence current controller of negative sequence components,the simulation results show that the controller can eliminate the negative sequence current and negative sequence current caused by the fault,the fault current is three-phase symmetrical;based on the basic principle of distance protection,negative sequence current control system of MMC-HVDC system does not affect the measured impedance,that does not change the reliability of the conclusion,because of the negative sequence current controller influents the negative sequence network,thereby affecting the zero sequence current.Finally,the operation of the negative sequence current controller of HVDC system eliminates the negative sequence current,making alternating current three-phase symmetrical,current-difference sudden-change component is failing,choosing fault phase selection based on the characteristic of low voltage fault phase.During the AC system occurs an asymmetric fault,design the control strategy for the control system of HVDC,theoretical analysis of the impact of control strategies for AC line distance protection,zero sequence current protection,current superimposed phase selector protection,build a theoretical model to verify the results in the corresponding PSCAD/ EMTDC simulation software.This paper provides a theoretical basis for the protection configuration and setting of the transmission system with MMC-HVDC,which provides a guarantee for the safe and stable operation of the power grid.