Changeover method of hvdc transmission system

A changeover method of a high voltage direct current (HVDC) transmission system is provided. A first system is set to an active state. A ready signal is transmitted from the first system to a first COL. A ready detection signal and an active signal are transmitted to the first system, in response to the ready signal. A confirm signal is transmitted to the first system in response to the active signal when the ready detection signal matches the ready signal.