A Novel Recovery Strategy to Suppress Subsequent Commutation Failure in an LCC-Based HVDC

Abstract

A subsequent commutation failure (SCF) can easily occur during the recovery process after a first commutation failure (1st CF). This paper analyzes the interaction mechanism of extinction angle, AC voltage, DC current and firing angle, and reveals that the complex coupling relationship during the dynamic process after the 1st CF has a significant effect on the SCF. The mathematical equations when considering different fault durations, fault severities and AC system strengths are then established. An AC fault voltage detection method based on reactive power and fault duration is also proposed to measure the fault severity, and an SCF inhibition control strategy (SCFICS) based on AC fault detection and reactive power control is subsequently proposed. This can not only inhibit the SCF, but also enhance the DC recovery speed effectively. Finally, based on the SCFICS, a simulation model is built, and the simulation results with different cases indicate that the SCFICS can effectively inhibit the SCF with good recovery performance, for three-phase-to-ground (TPG) and single-phase-to-ground faults, and with a fault inductance range of 0.01 H to 1 H.