This invention discloses an active injection-type fault nature identification method for wind farms connected to the grid via flexible DC transmission lines, belonging to the field of power
system relay protection technology. S1. After a fault occurs, the sending-end MMC converter
station detects a change in the
circuit breaker state, exits the original V-f control strategy, and sets the modulation wave to zero, causing
power loss on the AC side of the sending-end MMC converter
station; S2. After waiting for the fault
arc extinction time, the
circuit breaker is reclosed, establishing a current injection channel; S3. The sending-end MMC converter
station outputs a three-phase symmetrical
sinusoidal modulation wave, which is processed to generate a
switching signal, activating the capacitors of each phase bridge arm submodule, injecting a
voltage detection
signal into the AC side of the faulty line; S4. Based on the difference in the amplitude of the current
signal generated by the
voltage detection
signal, the fault nature of the line is identified. This invention can accurately identify the fault nature of wind farms connected to the grid via flexible DC transmission lines, shorten power restoration time, improve
system operational reliability, avoid
overcurrent during the identification process in the event of severe faults, and has high sensitivity to high-resistance faults.