| Interconnection of regional power grids is the inevitable trend of development of Chinese power grid . Projects of power transmission from west to east and mutual power supply for south and north not only solve the problem of imbalance between resources distribution and its demand , but also the objective needs of the power industrial development in our country. High-voltage direct current(HVDC) transmission, which is suit for transmission long distance and large capacity, will become one of the main ways of electric grid interconnection.As a highly controllable system, the controller performance of HVDC transmission system is the strong guarantee for normal operation of direct current transmission system. Therefore, the study of HVDC transmission system is a practical thesis.At present, Conventional control method in the HVDC transmission control applications is still traditional controller. But the HVDC transmission system is a typical strong non-linear, time-varying systems, the classic controller is difficult to ensure that the system can operate normally at all of the operating mode. For the problem of self-adaptive deficiencies consist in the traditional adaptive controller, the author focused on the theory of fuzzy control and neural network control in the application of DC control system. And then designed a intelligent controller, which can real-time response to variation of the system so as to solve a complex nonlinear and uncertain problems of the power system, by combine with the traditional control techniques.Firstly, the author introduced the theoretical systems of the HVDC transmission system, including the basic principles and composition of direct current transmission system as well as features of the major components. Due to converter is the most important element of the DC transmission project,the author discussed the working principle and characteristics of twelve-pulse converters in detail for the groundwork of the theoretical research in the system control strategy. Based on the establishment of a system model, The author analyzed DC transmission systems control mechanism in detail.Then,The basic control mode which are the rectifier-side was used constant-current control and inverter-side was used voltage control, was determined. At the same time, the basic control block diagram was given out.After then, the fundamental principles of fuzzy and neural network control were discussed in detail in the paper,and applied in the controller of HVDC transmission system.Finally, the author designed an intelligent controller which were based on the fuzzy control and neural network technology. a twelve-pulse HVDC system simulation model was built with MATLAB.The designed control strategy of the controller was simulated: (1)When AC single-phase ground fault was happened at rectifier side of the system,the traditional PI control and fuzzy,neural network control method and so on were adopted to simulate and all the dynamic response curve in various control strategy will be compared; (2)When DC circuit ground fault was happened,the traditional control and intelligent control method were adopted to simulate,And with the rectifier,inverter side are used in the traditional PI control strategy dynamic response curve will be compared.The results of simulation show that: Compared with the traditional PI control, intelligent control has more value in application which have shown a strong advantage at the following performance and the recovery after fault and so forth. Therefore the intelligent controller was designed in the paper which is more robust and adaptive learning ability,and good dynamic performance. |
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