Coordinated Reactive Power Control Strategies Considering The Coherence Of Generators For Wind Farms And Researches Of Its Operation Characteristics Connected To The Grid

As a clean, non-polluting and renewable energy, wind power has been developing rapidly around the world. Large-scale wind power integration also brings new challenges to safe and stable operation of the grid, which the voltage and reactive power control issue is one of the most important problems to be solved. To analyze the relationship between the reactive power and system voltage of the wind farm, the differences and similarities of generating units’ operating characteristics should be taken full account, based on the complete model and associated data. From the perspective of the wind farm, this paper considered the coherence of generating units from the point of operating characteristics and the Crowbar protection’s action, to explore the effectiveness of coordinate reactive power control strategy considering the coherence of generating units.This paper simply described the mathematical model of doubly-fed induction generator (DFIG), then established the rotor-side converter’s control strategy based on stator flux oriented, grid-side converter’s control strategy based on grid voltage oriented and related protection system. Low voltage ride-through (LVRT) control strategy was also established according to the LVRT requirements from the grid code for DFIG, and simulations verified the validity of the control strategies above. Secondly, generating units in the wind farm were divided to coherent clusters depending on the differences and similarities of the generators’ operating characteristics, then constant voltage control strategy and constant power factor control strategy were applied to different clusters due to their different operating characteristics.And also a wind farm stability coefficient synthetically considering the grid voltage stability and reactive power margin was adopted to evaluate the wind farm’s reactive power control strategy. The simulation results showed that the proposed reactive power control strategy considering coherence of generating units could effectively support grid voltage and there existed a relatively large reactive power margin to meet the reactive power requirement of power grid. Finally, the paper analyzed LVRT characteristic of DFIGs using Crowbar protection, and proposed an improved grid-side converter control strategy to give full play to the grid-side converter when the Crowbar protection circuit operated. A reactive power control strategy of wind farm based on Crowbar’s action was proposed, and different clusters adopted different reactive power control strategy. The simulations showed that the control strategy effectively improved the LVRT capability of wind farm.