Control System Models For Ultra High Voltage Direct Current Transmission

Ultra High Voltage Direct Current (UHVDC) transmission has the characteristics of long-distance transmission, large capacity, flexible control, low power loss, land saving and so on, it is playing an increasingly important role in the west to east power transmission project and market resource allocation. It is very significant for safe operation of power system and healthy development of national economic. Until around2020, fifteen UHVDC projects will be built and connected to domestic power grid, they contains about thirty converter stations and26000km long transmission line, the transmission capacity will be94400MW. Ultra High Voltage AC/DC parallel operation of synchronous power grid covers North China,Central China and East China region.Some UHVDC transmission projects have been completed and put into operation in succession. Increasingly closely connection of AC system and DC system that makes the grid structure more complicated. Therefore, higher requirements for reliability and control of the UHVDC transmission system are put forward. Control system is the brain of UHVDC project. In order to do well of the research of UHVDC transmission system, we need an accurate simulation model of the control system.The UHVDC develops based on the HVDC, their basic principles and characteristics of the control system are similar. The hierarchical structure and module function of the UHVDC transmission control system are introduced detailedly in the thesis. The control system of bipolar-control and polar-control functions are simplified. Making use of the RTDS simulation software, the simulation model of select type control system was set up which the valve unit control plays a central role. The model not only can fully reflect the UHVDC control characteristic of the control system, but also can speed up the simulation so as to be easily understood.It is proved by simulation that all of the parameters meet the requirements of design when the UHVDC is in the steady-state operation. The accuracy of the control model is testified with simulation in the following three cases:rectifier outlet side DC line earth fault; AC system single-phase earth fault on the rectifier side; AC system three-phase short circuit on the inverter side. The research results of the thesis are of great significance for the further study of domestic high-voltage DC control system and AC/DC hybrid transient simulation.