Feasibility Study On Multi-terminal Feed For High Voltage Direct Current Transmission

With unceasing increase of traditional HVDC transmission capacity, it became more and more obvious that the voltage supporting ability of receiving end power system restricts the development of HVDC power transmission, which also blocks the application of HVDC. So that traditional HVDC transmission can not meet the growth in power demand of ultra-high capacity and ultra-long distance.Because of these, a multi-terminal feedfor HVDC is proposed innovativelyin this paper. Steady-state and transient characteristics are analyzed to certify its feasibility.Firstly, began with background and significance of this paper, the technology of commutation devices andHVDC are generalized. Meanwhile, the present research situation are concluded. To study multi-terminal feed for HVDC in depth, structure and control system are introduced in detail. Based on PSCAD/EMTDC, simulation model for multi-terminal feed for HVDC is built. PI parameters of controller are optimized with Optimum Run.According to nodal impedance matrix, short-circuit ratios of the receiving end system under different infeed modes are derived and the contrastive analysis of them are performed. Taking ±800kV UHVDC transmission project from Xiangjiaba to Shanghai and ±500kV HVDC transmission project from Deyang to Baoji as examples, the short-circuit ratios of receiving end systems and power transfer characteristic curves under different infeed modes are compared to validate the superiority of multi-terminal feed. From the aspects of the inter-connection, the control strategies, the extension and the construction cost of HVDC transmission system, the advantages and disadvantages of various infeed modes are listed.In the fourth chapter, start-up and ac/dc short circuit to ground are analyzed. Response mechanism for multi-terminal feed are given in detail and are verified by transient characteristics simulation. Concluded that multi-terminal feed can get better start-up and transient characteristics when rectifier station works as voltage station, which is different from traditional point to point HVDC.