Multi-timescale Reactive-power Support of Doubly Fed Wind Turbines during Grid Transients

Power systems with high renewable-energy penetration increasingly demand that generating units provide support during grid transients. The physical structure and control system of doubly fed wind turbines determine whether they can provide reactive-power compensation at multiple timescales during grid-transient processes. By analyzing the transient characteristics of doubly fed wind turbines at different timescales during faults, a joint multi-timescale coordinated control strategy, including doubly fed wind generator instantaneous spontaneous reactive-power compensation, grid-side converter fast reactive compensation, and rotor-side converter (RSC) compensation, is developed. A back electromotive force generated from the stator transient flux is applied to the RSC control loop as dynamic feedforward compensation, which together with reactive reference value optimization and virtual resistance, achieves fault ride-through without crowbar operation during faults. Simulation models of the doubly fed wind turbine connected to the AC grid and sent out via line-commutated converter-based high-voltage direct current (LCC-HVDC) are constructed in the PSCAD/EMTDC simulation platform to verify the superiority of the proposed control strategy for multi-timescale reactive-power compensation.