Analysis of Hybrid LCC-VSC HVDC Transmission Systems

High Voltage Direct Current(HVDC) is widely considered as an efficient and economical option for long distances transmission of electric power compared to ac transmission. Conventional HVDC transmission is based on line commutated converter(LCC). Although this mature technology has large transmission capacity, it still has some disadvantages such as risk of commutation failure, lack of black start capability and large reactive power consumption. Voltage source converter(VSC) based HVDC is a more recent technology that provides higher operational flexibility including independent control of active and reactive power as well as black start capability. However, VSCs have higher switching losses and construction costs compared to LCCs. On the current stage, Hybrid HVDC with LCCs and VSCs presented a promising alternative solution that combines the advantages of both converter topologies: reduction of power losses and cost and higher control flexibility. The research work of the master thesis will be carried out under the guidance of Prof. Oriol Gomis and Dr. Marc Cheah with the support of CITCEA and department of electrical engineering, ETSEIB. As a part of the thesis work, the basic structure of HVDC system, LCC-HVDC and VSC-HVDC will be analyzed at first. A literature review of hybrid LCC-VSC HVDC system and a case study will also be presented in the thesis. The analytical models will be established to verify our designed controller and demonstrate the features of these two different converter topologies. On the basis of the analysis above, a double-ended hybrid HVDC system will be built by interconnecting the LCC converter and the VSC converter to investigate different operating principles and control strategies.