Unidirectional HVdc Topology With DC Fault Ride-Through Capability

HVdc transmission using modular multilevel converters (MMCs) is becoming increasingly prevalent. However, line-commutated converter (LCC) HVdc transmission remains advantageous in its ability to clear dc faults and restart power transmission without operation of the ac system protection. This paper presents an HVdc system topology that employs both MMC and LCC converters to transmit unidirectional power into weak ac systems while retaining the ability to clear dc faults. Control strategies and performance under dc and ac faults are discussed and demonstrated using electromagnetic transient simulations.