A hybrid power flow controller based on a cascaded H-bridge (“hybrid power flow controller”) is a flexible AC transmission system technology that has good effects in adjusting grid power flow and improving transmission line carrying capacity. To avoid line protection rejection when asymmetric faults occur

which affects the stable and safe operation of the converter

this paper proposes an asymmetric fault crossing strategy of the hybrid power flow controller based on negative sequence voltage compensation. The scheme uses the cascaded H-bridge converter as a controlled voltage source to provide a negative sequence voltage compensation with controllable amplitude and phase angle on the phase shift transition equivalent negative sequence impedance

achieving fault crossing of the hybrid power flow controller. The negative sequence component of the measured current is used as the basis of asymmetric fault identification. The PST gear is quickly zeroed and switched simultaneously. The negative sequence current is controlled by measuring the negative sequence current to control the converter output negative sequence voltage for compensation. The measured negative sequence voltage and current are used to calculate the measured impedance

and the distance protection of the connected line operates normally after the hybrid power flow controller is connected. Finally

a simulation model of the hybrid power flow controller connected to the line is built on the PSCAD/EMTDC platform

and a large number of simulation experiments are carried out to verify the feasibility and effectiveness of the proposed scheme.