Grid Synchronization of Grid-side Converter in Direct Drive Wind Power Generation System Under Grid Faults

It is essential for accurate and fast detection of fundamental frequency positive-and negative-sequence component of the utility voltage under grid fault to keep the control over the power exchange with the grid to avoid trip of the converter protections and to allow the ride-through of the transient fault.We proposed a new technique for grid synchronization of grid-side converter in direct drive wind power generation system under unbalanced and distorted conditions,i.e.,the dual second order generalized integrator frequency-locked loop(DSOGI-FLL).The proposed detector includes three fundamental function blocks,namely,the quadrature-signals generator(QSG),positive-and negative-sequence calculator(PNSC) and frequency-locked loop(FLL).Moreover,the DSOGI-FLL was studied by simulation and experiment.The obtained simulation and experiment results demonstrate that this new software phase-locked loop is easy to implement by digital and can detect and track asymmetrical and distorted grid voltage rapidly and accurately,and the results indicate that the DSOGI-FLL is a very suitable solution for grid synchronization of grid-side converter in direct drive wind power generation system under unbalanced and distorted conditions.