Power Conversion System and Control Device for Same

A power conversion system including: a first self-commutated converter connected between a first AC power system, and a first DC main line and a DC return line for first high voltage DC transmission; a second self-commutated converter connected between the first AC power system, and the DC return line and a second DC main line for second high voltage DC transmission; and a control device, wherein when detecting a single or double line to ground fault inside the second self-commutated converter and detecting an occurrence of a missed zero crossing in a non-faulted phase of the first AC power system, the control device causes the first self-commutated converter to output a DC component for eliminating the missed zero crossing to the first AC power system, and then opens an AC circuit breaker in order to separate the second self-commutated converter from the first AC power system.