In view of the inadequacy of the present research on commutation failure merely focusing on voltage drop without considering the rise of DC current

a complete commutation failure analysis model with the operating parameters of rectifier side

inverter side

and DC transmission lines taken into account is developed based on the classical turn-off angle expression. According to the influence of AC voltage drop on the DC current rise

the model can decouple AC voltage and DC current to obtain a single relational expression between the turn-off angle and the commutation bus voltage. Then the critical commutation voltage value and the critical voltage drop speed causing commutation failure are derived based on the above model. The theoretical derivation of relations between the voltage drop speed and fault severity and reactive power compensation capacity is also carried out. It is found that the voltage nonlinearly drops faster with the fault severity. In some earlier commutation processes

the larger the voltage drop amplitude is

the more likely the commutation failure will be. The PSCAD/EMTDC simulation results prove the proposed method.