Assessment of fault-ride through capability of grid-connected brushless DFIG wind turbines

DFIGs are reported to suffer serious reliability problems due to the presence of slip-rings, brushes and gearbox. These disadvantages encouraged several research groups to investigate the viability of employing single-frame or double frame Brushless Cascade DFIGs (BCDFIGs) in grid connected multi-megawatt wind turbines especially off-shore and in solar chimney power plants. In this regard, this paper tackles three main issues. Firstly, the expected reduction in gear ratio and maintenance frequency and cost by replacing DFIGs with BCDFIGs of the same power. Secondly, a detailed comparison is held between DFIG-WTs and BCDFIG-WT regarding their behaviour under unbalanced grid voltage. Finally, the paper studies to what extent a multi megawatt BCDFIG-WT is grid code compliant by its nature in terms of fault ride-through capability. This is illustrated by comparing and quantifying the response of a DFIG-WT and a BCDFIG-WT to a severe three phase voltage dip. Results indicate a promising behaviour of BCDFIGs during disturbances.