Research On Transient Stability Of Grid Connected Photovoltaic Generation System

With the rapid development of photovoltaic industry and the strong support of government policies,China's installed capacity of photovoltaic power is growing at an increasingly fast speed,and its proportion to the total grid power supply is rising continuously. For its different characteristics from conventional power sources, photovoltaic power's influences on power system transient stability should be analyzed and researched before its large scale grid connection.In order to conduct the simulation and research on transient stability of a power grid with photovoltaic power generation system, this paper established a electromechanical transient model of a photovoltaic power system.Firstly,a reasonable assumption of photovoltaic power generation system was done, ignoring some elements which are unnecessary under the conditions of electromechanical transient simulation.On the basis,a system structure suitable for grid connected photovoltaic system is designed,and the models of the components of the system are established, including photovoltaic array, inverter and its control system,maximum power point tracking scheme and grid connecting filter. Then the models of the components are transformed into differential equations and algebraic equations which are suitable for programming.The model of a photovoltaic system connecting to a infinite bus system was realized using MATLAB programming means,and the photovoltaic model is validated through MATLAB simulation.The dynamic process of the DC-DC conversion circuit is ignored in the modeling assumptions above, and the correctness of the assumption should be proved through the response speed of the DC-DC conversion circuit.First, the model of the DC-DC conversion circuit is established using the state space averaging method,then the selection of parameters and response time range are analyzed, proving the correctness of this assumption.Transient stability analysis of power system with grid connected photovoltaic power generation system is conducted using the established model of photovoltaic system.Through simulations of a small power systems and a large power system, the influence of solar power fluctuation,low voltage ride through capability and small inertia of photovoltaic power sources on power system stability is researched.