To meet the need of rapid accurate simulation of the large-scale AC/DC hybrid power system

dynamic phasor method is applied to a model of line commutated converter under unbalanced conditions. Firstly

the principle of switching instants and commutation under unbalanced conditions is analyzed. A calculation method for triggering angle and commutation angle considering the third harmonic at AC as well as the second harmonic at DC is established. The traditional switching function model is improved for unbalanced conditions. Also

calculation process is simplified by ignoring non-essential harmonics

and an advanced dynamic phasor model for the line commutated converter

which is suitable for normal operating and unbalanced conditions

is proposed. Based on the Cigre-Benchmark DC system

the model has been compared with the simulation results from PSCAD

and the result shows the effectiveness of the model. Based on the improved switching function model

the failure of the commutation is further determined. The result shows that the failure of the commutation can be determined efficiently by considering the second harmonic at DC and the third harmonic at AC.