Simulation of DFIG wind turbines for transient studies: An alternative approach based on symbolic–numeric computations

Abstract

This paper describes an alternative approach based on symbolic and numeric computations to simulate wind turbines equipped with doubly fed induction generator (DFIG). The actuator disk theory is used to represent the aerodynamic part, and the one-mass model simulates the mechanical part. The 5th-order induction generator is selected to model the electric machine, being this approach suitable to estimate the DFIG performance under transient conditions. The corresponding non-linear integro-differential equation system has been reduced to a linear state-space system by using an ad hoc local linearization. This novel symbolic–numeric computation (SNC) method has been implemented by using two different software-packages, with the purpose of solving simultaneously a remarkable number of individual wind turbine models submitted to different wind speed profiles and/or grid voltage waveforms.The obtained results are compared with traditional finite difference discretization (FDD) methods, widely proposed for this type of studies. The results offer a remarkable agreement between the proposed SNC method and the FDD solutions, considering variations of both wind speed profiles and electrical transient events. In this way, real voltage dips collected in Spanish wind farms are used as input voltage waveforms to evaluate the suitability of the proposed solution under transient disturbances when a large amount of individual wind turbines are simultaneously simulated. In this way, a comparison of computational time costs considering different number of wind turbines and integration time-steps is also included in the paper. From this comparison, the proposed SNC method presents clear advantages in terms of computational time cost requirements under both steady-state and transient studies.