Modeling and Analysis of Brushless Doubly-Fed Induction Generators with Non-Ideal Grids

Brushless Doubly-Fed Induction Generators (BDFIG) increase reliability and decrease maintenance cost because it removes the brushes and slip rings of the traditional Doubly-Fed Induction Generator (DFIG). It has a potential for wide application in power generation systems. Non-ideal characteristics such as symmetrical and asymmetrical dips in the grid voltage are inevitable in power generation systems. Running BDFIG in a non-ideal grid will produce low-order harmonic oscillation, which will cause the distortion in the winding voltage, resulting in serious overvoltage and overcurrent faults in motor winding, reducing the reliability of the entire power generation system. In order to provide more targeted protection for BDFIG under non-ideal grid operating conditions, this paper establishes the BDFIG model with the non-ideal power grid and analyzes its working characteristics. Firstly, establish the BDFIG model under the ideal grid and obtain the voltage characteristics of the control winding from analysis of when the power grid fails; Secondly, establish the BDFIG model under the non-ideal grid and analyze from two cases of balanced grid with low harmonic voltage and unbalanced grid with low harmonic voltage respectively. Thirdly, the relational equations of the positive and negative sequence components are derived respectively, which provides a theoretical basis for the control of positive and negative sequence components; Finally, the characteristics of BDFIG under non-ideal grid are simulated and verified by Matlab/Simulink.