Analysis and Mitigation of Electromechanical Oscillations in Drivetrain for Hybrid Synchronization Control of DFIG-Based Wind Turbines

The power-synchronized control (PSC) satisfactorily functions in weak grids; however, its slow dynamic response is not compatible with the grid-forming doubly fed induction generator-based wind turbines (DFIG-WTs) in drivetrain, which will induce electromechanical oscillations. Hybrid synchronization control (HSC) is proposed from a new perspective to achieve a higher compatibility, which coalesces the
dq
-axis voltage loop between the phase-locked loop-synchronized control and PSC. The HSC has the advantages of high flexibility, strong adaptability of grid, and adjusted dynamic characteristics. To better describe the system, considering the implemented rotor speed control and drivetrain model, the linearized small-signal model of the HSC DFIG-WTs is established to reveal the electromechanical dynamic interaction between the strength of grid and drivetrain system. Theoretical analysis shows that two resonant peaks in the system appear, which correspond to the torsional oscillations of the drivetrain and low-frequency oscillations of the electrical system. In addition, an appropriate position is selected to increase the torque damping to fulfill the stability requirements of HSC-DFIG WTs. Finally, the correctness of the theoretical analysis is verified using the hardware-in-the-loop experiment.