Research On Equivalence Model Of Wind Farms For Numerical Simulation

Wind farm’s impact on the stability of power system has became more and more obvious, and the equivalent model of the wind farm is important for the analysis of the influence of wind farm on power system reliability. In this essay, the SCIG and DFIG will be taken as examples to conduct a deep research and analysis on the equivalent model of wind turbine and its wind farm.According to the mathematical model of SCIG and DFIG, it’s simulation model could be established by S-Function and basic modules in Matlab/Simulink respectively. The model could be applied to set up a simulation model of wind farms composed of SCIG and DFIG. In the model, voltages and currents are designed as the input variables and the output variables respectively, which makes the solving of computer-grid equations much easier.Meanwhile, trapezoidal method is utilized to establish the discrete time domain Thevenin equivalent model of m-r axis in SCIG and d-q axis in DFIG, reflecting a function between terminal voltage and current of wind generators, on the basis of the linear mathematical model of SCIG and DFIG. In order to verity the validity and correctness of the model, a simplified system is used to operate in different system conditions with wind speed disturbance and network failure etc. In terms of the accuracy of the model, to a large extend, it lies in the linearization method of wind turbine model as well as the numerical integration step sizzle. Compared with the model using S-Function in the Matlab/Simulink, the discrete time domain Thevenin equivalent model have high stability and accuracy of numerical calculation.Based on the discrete time domain Thevenin and Norton equivalent model, this paper proposes a novel establishment approach on the equivalent model of wind farms, and elaborates how to determine the discrete time domain equivalent model configuration and corresponding parameters of wind farms in case of same wind speed and wind turbine parameters and the case of different wind speed and wind turbine parameters. The accuracy of wind farm equivalent model depends on that of the wind turbine equivalent model. The model can readily realize the wind farm simulation under different operating conditions, and it can achieve the simulation about the influence of control unit in DFIG on the transient behavior of wind farms. The proposed wind farm equivalent model has better accuracy and stability of numerical calculation. The simulation is operated on WSCC system with three generators and nine buses using the wind farm equivalent model, whose consequence is the same as the one of the detail model. Thus, the proposed establishment approach of wind farm equivalent model has application value.