Improving voltage stability by utilizing reactive power injection capability of variable speed wind turbines

The impact that wind turbines have on the voltage stability is investigated in this paper. In particular, the effect of utilizing the reactive power injection capability of modern wind energy converters is investigated. It is found that reactive power injection from the wind turbine can increase the voltage stability of the power grid substantially, as well as moderately increase the steady-state power transfer limit. For a high wind speed situation, where the wind turbine converter is fully utilized, it is found that it isworth reducing the active power production from the wind turbine in order to make room for reactive power injection, from a voltage stability point of view. An interesting observation is that a modern variable speed wind turbine constantly operating at maximum power factor does not provide much voltage stability improvement compared to a traditional fixed-speed system under its usual operating condition, i.e. at lower wind speeds. The finding isthat the worst case to handle, from a voltage stability point of view, is the case where there is a high load demand, irrespective of the wind speed situation