AC Fault Ride-Through Capability of a VSC-HVDC Transmission Systems

This paper presents a recovery strategy that enables DC transmission systems based on voltage source converters to ride-through different ac faults with minimum current and voltage stresses on the converter switching devices. The proposed recovery strategy eliminates the trapped energy in the dc link during ac faults; as a result the rise in the dc link voltage is prevented. This may eliminate the need for the dc chopper in the dc link, as proposed in the literature, to dissipate the trapped energy. To demonstrate the effectiveness of the recovery strategy, several fault conditions are considered, including, symmetrical and asymmetrical faults. The proposed recovery strategy improves the resiliency of the VSC-HVDC transmission system to different ac faults, which can be summarized as follows: limited current contribution to the fault and limited current and voltage stress on the switching devices as the rise in the dc link voltage is significantly reduced or prevented.