A synchronization control technique for soft connection of doubly-fed induction generator based wind turbines to the power grid
Due to network events and power system emergencies, doubly-fed induction generator (DFIG) based wind turbines can suffer from low voltage ride through which may result to the disconnection of the DFIG. Before connecting to the electricity grid again, DFIG has to be synchronized to minimize the transient effects and ensure smooth connection to the power grid. In this paper, a direct voltage control based synchronization technique is proposed for DFIG based wind turbines. Additional control features are added to original direct voltage control method for implementation of the proposed synchronization strategy. A grid connection logic is designed and presented for soft connection of DFIG to the grid. The proposed technique is implemented in a DFIG based wind turbine model and tested through simulations with various practical scenarios. Voltage transients, frequency analysis, voltage phase and system stability are analyzed in details and simulation results presented. From the results, it can be revealed that the proposed synchronization technique functions effectively and efficiently. It is also shown that by using the proposed technique, the process of synchronization and grid connection do not introduce any changes into the system, which may cause protection devices to trip or mal-operation.