Research On Power Flow Controlling In DC Grid

With the environmental problems which come from traditional energy being increasingly serious, renewable energy plays an increasingly large proportion. HVDC Technology based on voltage source converter (VSC-HVDC) enables smooth access to renewable energy. Traditional VSC-HVDC system is generally radial connection, which means there is only one transmission line between the two converter stations. In recent years, with the development of the DC grid, which appears a plurality of parallel lines between the two converter stations in many complex grids. However, the current trend not only be decided by the voltage between the converter, but also be decided by the line resistance, which means that the trend of the DC power grid can not be completely controlled by the converter station. In this situation, some lines will create too much loss and even overload. In view of this situation, the additional power flow controller is necessary to prevent circuit overload and achieve economic operation.In this paper, the DC power flow control was mainly researched. Firstly, it introduces the basic characteristics and composition of the voltage source converter.The is the core of the control system. The main control method of converter station is the direct current control. Then the control performance was verified by simulation. Secondly, according to the disadvantage of the control of the converter station, power flow controller (PFC) is proposed. Then, several DC power flow controller which had been were analyzed through works and operating characteristics. In contrast, series voltage source is the best so far. Two improvements topology of the series voltage source have been proposed and then the feasibility of the series voltage source was verified through the simulation. Finally, a new method of location selection for PFC based on Sensitivity was proposed. This method was verified through an example and simulation.