Auxiliary Control of Grid-Connected for Wind Farm Based on Flexible DC Electric Power Transmission

Aiming at the voltage instability caused by the application of AC and DC wind power grids in long-distance large-scale wind power sites, a voltage and frequency auxiliary control strategy is proposed combining with traditional constant-voltage and constant-frequency control. Firstly, the structure and mathematical model of wind farm grid-connection based on flexible HVDC system are established. Secondly, the improved control mode of wind field side fixed frequency control and power grid side fixed DC voltage control are designed. Then, wind speed disturbance is added through DC voltage and frequency auxiliary control. Finally, a flexible DC power transmission system model for wind power access is established under the PSCAD/EMTDC platform and the control instruction is input into the receiving system of converter stations on the both sides. The simulation results show that the proposed control strategy can reduce the harmonic content and power fluctuation of the system, improve the voltage stability and the system stability when the DFIG is connected to the flexible DC grid.