Abstract
This paper presents a coordinated control strategy for a hybrid wind farm with doubly-fed induction generator (DFIG)- and direct-driven permanent-magnet synchronous generator (PMSG)-based wind turbines under symmetrical grid faults. The proposed low-voltage ride-through (LVRT) strategy is based on a novel current allocation principle and is implemented for individual DFIG- or PMSG-based wind turbines. No communication equipment between different wind power generators is required. By monitoring the local voltages and active power outputs of the corresponding wind generators, the proposed control strategy can control the hybrid wind farm to provide the maximum reactive power to support the grid voltage during a symmetrical grid fault. As a result, the reduction in the active power output from the hybrid wind farm can be decreased, which also helps avoid generator over-speed issues and supply active power support for the power grid. In addition, the reactive current upper limits of DFIG- and PMSG-based sub-wind farms are investigated by considering different active power outputs and different grid voltage dip depths, and the feasible regions of the two types of sub-wind farms for meeting the LVRT requirements are further studied. Finally, the effectiveness of the proposed coordinated LVRT control strategy for the hybrid wind farm is validated by simulation and experimental results.
Highlights
With wind energy penetration levels to the power systems rapidly increasing, the impacts of large-scale wind power generation systems on power grids have become much more significant than ever before [1,2]
For the low-voltage ride-through (LVRT) control method of hybrid wind farms, the proposed control strategies in [10,11] can effectively improve the operation performance of the hybrid wind farm consisting of fixed speed induction generators (FSIG)- with doubly fed induction generators (DFIG)- or permanent magnetic synchronous generators (PMSG)-based wind turbines under grid faults, there are still some drawbacks in the strategies
Where Ug_D is the stator voltage, namely the voltage at the terminal of the DFIG-based sub-wind farm; Qs_D is the reactive power output from the DFIG stator; Ls is the total inductance of the stator winding; Lm is the mutual inductance between the stator winding and the rotor winding; isd_D and isq_D are the stator d- and q-axis currents, respectively; ird_D and irq_D are the rotor d- and q-axis currents, respectively
Summary
With wind energy penetration levels to the power systems rapidly increasing, the impacts of large-scale wind power generation systems on power grids have become much more significant than ever before [1,2]. Coordinated control strategies were proposed in [10,11] for hybrid wind farms with DFIG- and FSIG-based wind power generation systems during symmetrical grid faults. For the LVRT control method of hybrid wind farms, the proposed control strategies in [10,11] can effectively improve the operation performance of the hybrid wind farm consisting of FSIG- with DFIG- or PMSG-based wind turbines under grid faults, there are still some drawbacks in the strategies. Different from DFIG-based wind turbines, utilizing full-rated converters which are connected between the generators and the power grid, PMSG systems have the advantages such as high power density, high grid voltage fault controllability, and simple control method, except high initial installation costs [18,19,20].
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