Improved Active Current Control Scheme of Wind Energy Conversion Systems With PLL Synchronization During Grid Faults

In this project, Wind energy conversion systems (WECSs) depend upon phase-locked loops (PLLs) for synchronization with the power grid. As the voltage dip during g02

1rid faults lowers the transfer capacity between WECSs and the grid, PLLs may suffer loss of synchronization (LOS) if the active current reference of WECSs exceeds the transfer capacity. To analyze the PLL synchronization stability, a U-Id plane analysis method is presented. The transfer capacity constraint and the WECS active current control scheme are mapped to the U(Id) curve and control curve in a U-Id plane, respectively, describing the relationship between the terminal voltage and the WECS active current. Hence, the influence of grid parameters and the WECS control scheme can be analyzed separately. Accordingly, to prevent LOS, an improved active current control scheme of WECSs is proposed based on the short circuit ratio. The scheme corresponds to a control curve in the U-Id plane that ensures the existence of stable equilibrium points and is quite easy to apply in practice. The simulation results can be evaluated by using Matlab/Simulink Software.

Keywords: Wind energy conversion systems, fault ride through, active current control, PLL synchronization stability.