The actively commutated current-source-converter (ACC) is a promising converter topology for constructing a novel DC transmission system with no commutation failure

black start and AC/DC fault ride-through capability. However

there are commutation capacitors at the AC outlet of the ACC valve. The coupling transient behavior of the capacitors' voltage under the effect of the filter inductance and the input energy of the AC system as well as the circuit structure change caused by the valve commutation under the control system will affect the DC fault current. The existing methods can't quantitatively analyze the fault characteristics

which is not conducive to system planning and protection design. Therefore

this paper proposes an ACC-HVDC DC fault analytical method with preferably accuracy by considering the changing state of the LC filter caused by the AC system and the influence of DC controller and phase-locked loop on the switching state after fault. Firstly

the steady-state frequency domain model of the LC filter is constructed. Subsequently

a unified time-domain simplified model of DC current in the whole stage after fault is derived

and its development mechanism is analyzed. After that

based on the transient analytical model of post-fault commutation capacitors

filtering inductors

and control systems

the variation pattern of bridge arm switch states is analyzed to obtain commutation characteristic coefficients

achieving calculation of DC fault currents. Finally

a PSCAD electromagnetic transient model is constructed to compare and verify the accuracy of the proposed method.