Research On Control Mode And Operating Characteristic Of Novel HVDC Transmission System

The network interconnection of the whole country is a inexorable trend with the development of Chinese electrical network. Building"Transmission electrical power from West to East"and"Exchange electrical power between South and North"projects is the desirability for the unbalanced resources distribution and the unbalanced demands. It is also a necessary strategy of our power industry. UHV power grid will be the major development of SGCC, and DC transmission, which fits for transmitting electrical power in long distance and large capacity and will be widely used in UHV engineering. Converter transformer is one of the most important equipments in HVDC transmission system. The auto-compensator and harmonics suppression converter transformer has a very good application prospect for having the merits that traditional transformer doesn't. Control mode and operating characteristic of new type DC transmission system adopting novel transformer and its filter device are mainly studied in this thesis.The main works includes the following:At first, the principle and feature of novel transformer and its filter device are simply analysed, at the same time, the research and development platform for new transmission and distribution technology of Hunan University is introduced. The novel converter transformer's unique functions, such as auto-compensation and harmonic shielding, are mainly discussed.Then, gross structure of traditional HVDC control system is researched. And the polar-control system, a part of traditional HVDC control system, is mainly discussed. The principle and characteristic of various controller are set forth. Through simulation, the performance of controller, the switching behavior between different controllers after destabilization, the characteristics of the steady and transient states in the system are detailed studied.And then, by using PSCAD/EMTDC, a tool for electromagnetic transient simulation, a simulation model of novel DC transmission system adopting novel transformer and its filter device is established, and the model's operating characteristics at various fault are analysed, in order to verify the reasonableness of the simulation model.At last, synergetic control theory is introduced and applied to the simulation model of novel DC transmission system. The operating characteristics at start-up process and the case that the setting value of DC is fluctuating are studied. The result shows that synergetic controller can reach a more satisfactory effect than traditional PI controller.