A Variable Droop Frequency Control Strategy for Wind Farms that Considers Optimal Rotor Kinetic Energy

A variable droop control strategy for wind farms (WFs) that considers optimal rotor kinetic energy (RKE) is presented in this paper. The process for the control strategy is as follows. First, an optimized scheduling reserve mode (OSRM) is executed by the WF control center (WFCC) according to the deloaded rate orders issued by the dispatching center. Through coordinated optimization control for over-speed control and pitch angle control, more available RKE can be stored in each wind turbine (WT) under the OSRM than can be stored in conventional over-speed reserve mode (CORM). Second, the optimization results will be sent to a variable droop coefficient set module for each WT by the WFCC. Then, the sum of the available RKE capacity and the mechanical load-shedding capacity (the wind power curtailment) of each WT can be computed in real-time and used as a practical spinning reserve capacity to adjust the droop coefficient. In this way, the optimized available RKE stored in the WT under the OSRM can be fully released to participate in the droop frequency control. Finally, simulations are performed in PSCAD/EMTDC to verify the proposed variable droop frequency control strategy for WFs. The simulation results indicate that the capability of the primary frequency regulation would be further improved, especially for low or medium wind speeds.