Study On The Fault Calculation Method Of The Power Grid With Large Scales Of Wind Turbines And Its Application

Traditional fossil energy sources are being threatened by the serious problems such as resource shortage, air pollution and climate change, and the gradual replacement of fossil fuels by renewable energy will become an important direction of future energy development. Among various types of renewable energy power generation technology, wind power occupies an important position and has been widely applied in engineering with its mature technology, high utilization, low cost and rich resources.The generation model of wind power technology is mainly centralized access to power grid on a large scale. The increasing capacity of the wind turbines accessed into the power grid has adverse influence on the security and stability of the power grid, which is becoming more and more obvious. The current fed by the wind turbine is great difference from the current fed by the traditional synchronous generator during the fault. Therefore, not only can the traditional fault calculation method not meet the requirements of the fault analysis when a large scale of wind turbines integrated into power grid, but it also brings many new problems to the relay protection setting calculation, which directly affects the performance of the relay protection. In order to meet the requirements of the fault calculation and relay protection setting calculation for the power grid with after a large scale of wind turbines, this paper studies the fault calculation equivalent model of doubly-fed induction generator(DFIG) and permanent magnet synchronous generator(PMSG) widely applied in wind farm. On this basis, combined with the requirements of practical engineering application, a novel fault calculation method for the power grid with large scales of wind turbines is proposed and an appropriative fault calculation is developed, which can meet the requirements of the relay protection setting calculation.The current fed by PMSG during the fault is related to its control strategies, fault types and so on. In oder to establish the fault calculation equivalent model of PMSG, the fault current expressions of PMSG under symmetrical and asymmetrical fault are respectively derived according to its several typical strategies in low voltage ride-through. On this basis, the fault calculation equivalent model of the PMSG considering different control strategies is established. Moreover, the correctness of the model is verified by the simulation results.As the structure of DFIG is complicated, its fault current analysis and establishment of equivalent model are very difficult in fault characteristic research for wind turbines. In oder to establish the fault calculation equivalent model of DFIG, the fault current expressions of the stator current and DFIG's grid side converter under symmetrical and asymmetrical fault are respectively derived according to its several typical strategies in low voltage ride-through. On this basis, the comprehensive fault calculation equivalent model of DFIG considering grid side converter's current and different control strategies is established. The correctness of the model is verified by the simulation results. Further more, and the relationship between the magnitude and phase of grid side converter's current with the rotor speed is analyzed.On the basis of the above research, a novel fault calculation method for the power grid with large scales of wind turbines is presented according to the characteristics of wind turbines' fault calculation equivalent model, which is based on the iterative solution of nodal voltage equations, boundary condition equations and fault calculation equivalent model equations to calculate the fault current and voltage. Based on the proposed fault calculation method and combined with the requirements of practical engineering application, a set of appropriative fault calculation is developed to meet the requirements of the relay protection setting calculation. The simulation and application results show that the software has high accuracy and can meet the engineering application requirements.