Improved controls for LCC-VSC hybrid HVDC system

High Voltage Direct Current (HVDC) transmission systems continue to be an excellent asset in modern power systems. The classical HVDC system and VSC-HVDC system showed greater advantages in power transmission and industry. Meanwhile major disadvantages like commutation failure, reactive power requirement in classical system and high cost, high switching losses and inability to handle DC line fault in VSC-HVDC system lead to the invention of LCC-VSC hybrid HVDC system. With no commutation failure, less reactive power requirement and reduced losses, the hybrid system is best suited for unidirectional power transmission scenarios, such as power transmission to islands and remote load centers, where the construction of new transmission lines is prohibitively expensive. The present work aims to study various aspects of hybrid HVDC system. The emphasis will be on developing appropriate control schemes at both rectifier and inverter terminals for efficient operation of the hybrid system and achieve best performance of the system under steady state and transient condition. The simulation study is carried in the PSCAD/EMTDC environment.