Research On Protection Of Power Grid With Large Photovoltaic Power Station

With more and more large-scale photovoltaic power station was built and accessed to the grid, its position was becoming more and more important in the power system. However, due to the fluctuation and randomness of its own,large-scale photovoltaic power station brought many new challenges to the power grid. The Influence of photovoltaic energy on relay protection can not be ignored.And the influence were analyzed and studied, in a manner.Firstly, according to the newest provision for photovoltaic power plant accessing to grid, a low voltage ride through control strategy of fault was proposed.According to the fault control strategy, when the fell of the system voltage was not serious, the PV power plant would support the active power as far as possible, premised on meeting the requirements of reactive power, in order to maintain the system active power balance. However, when the fell of the system voltage was serious, the PV power plant would support reactive current at first, in order to provide more reactive power support.Secondly, a controlled current source model of photovoltaic power plant was established, which was controlled by the voltage of the point of common coupling and the maximum active power captured by photovoltaic power plant. This model can correctly reflect the output characteristics of photovoltaic power plant, in two cases of symmetrical fault and asymmetrical fault. Based on this, the fault circuit equation and its solving method was established, and the theory and method of fault analysis for power system with photovoltaic power station were proposed.Thirdly, the influence of photovoltaic power station accessing to the grid distance protection was analyzed, based on the fault analysis method. Because of the fault current of photovoltaic power plant, the measured impedance of distance protection was seriously affected, when non metallic fault occurred to transmission line. Which could cause the misoperation and refused to move of protection. On this basis, according to the relation of fault output current between photovoltaic power plant and power system,a new scheme for setting the distance protection value was proposed. It was right to set the distance protection value of the grid with large-scale photovoltaic power plant.The protection setting value could be adjusted to the change of parameter of PV power plant in real time.Finally, in order to verify the correctness of the theoretical analysis, taking an typical power system with photovoltaic power station in Lanzhou for example,simulation models was constructed in PSCAD, based on which a lot of simulationswere carried out, and the data were processed by Matlab. The simulation results showed the effectiveness and feasibility of the control strategy and the principle of setting distance protection value.