Hvdc Transmission System Analysis And Control Of,

The power grid of China is in the period with high speed of development and now the transition from big-area network to fully-meshed national power grid has come into being. With the application of HVDC and the implementation of many projects belonging to West Development, HVDC will play an important role in transmission from west to east and interconnection of power system. In the meantime, the wide application of HVDC causes many problems in technology and management items. Because HVDC is sensitive to the fault of AC systems connected to it, the dynamic behavior of AC systems exercises a great influence on the stability of whole interconnected power network. One of prominent features of HVDC is its controllability. It is essential to research the controlling theory and the coordination of controlling modes. Additionally, HVDC with weak AC system near inverter side will produce the operating problems since the performance characteristic lies on the weakness degree of AC system with respect to HVDC. Therefore, finding out the operating characteristic and rules of HVDC, which is important, will keep the systems running safely , stably and is conducive to make full use of its transmission capacity. The platform of PSCAD/EMTDC has been adopted to research these issues based on the typical HVDC model presented by CIGRE. The main studying work are shown as follows:1. By means of PSCAD/EMTDC the dynamic characteristic and fault restoration of HVDC are studied thoroughly when some kinds of AC faults occur. The simulation result indicates that HVDC system can restore to the normal state after a simplex fault arises in a short time.2. The reasons and many influential factors which results in the commutation failure and the measures escaping from it are researched. The emphases is on analyzing the relationship of the factors and the degree of impact on commutation failure.3. The thesis introduces the configuration and function of HVDC control system and the essential control mode of the converter station in detail. Based on the CIGRE HVDC system, it provides the steady response characteristics of all controller and explains further the control policies of them, analyzing these policies when different faults occur. The impact of the basic controlling modes on therestoration of voltage and power is also simply investigated. 4. Some issues are put forward which often appears in weak AC system such as commutation failure, stability of voltage, and fault recovery. The mechanism causing commutation failure is analyzed when AC system near inverter station is weak. Also based on the CIGRE HVDC system, the dynamic stability of HVDC with different SCR is tested, the impact of different var compensator on weak AC system is simulated and some policies resolving these problems are provided.