A Directional Pilot Protection Scheme Based on Transient Power Amplitude Ratio for MMC-HVDC Grid

Modular multilevel converters (MMCs) possess a restricted capacity to tolerate excessive currents, and complex fault characteristics make it a significant challenge to reliably identify the fault area within a short period. This paper derives the frequency-domain power expression at the converter outlet during the inverter's unresponsive phase of a fault, analyzes the frequency-domain power characteristics on both sides of the converter during forward and backward faults, and utilizes the convolution theorem to convert the frequency-domain power ratio into a time-domain transient power ratio. Based on this, a directional pilot protection scheme is proposed. The scheme uses the transient power amplitude ratio as its basis. Finally, offline simulations conducted in PSCAD/EMTDC show that the proposed protection can reliably identify the fault area under conditions of 600 Ωand 30dB.