Grid voltage control with wind turbine inverters by using grid impedance estimation

Currently, distributed generation (DG) units usually do not participate in the primary grid voltage control and inject power regardless. Only when the grid voltage level surpasses a certain threshold, these units shut down to avoid any overvoltage problems. In this paper, a method is developed to control the grid voltage by wind turbines. This way, the grid voltage level improves, and the wind turbine can still generate power under suboptimal grid voltage conditions. The effect on the grid voltage depends on the grid impedance ratio R/X. In this paper, the effectiveness of the grid voltage control is improved by estimating the grid impedance ratio in real-time to inject active and reactive power accordingly. The method is applied to wind turbines, but can be used for other DG units as well.