Reactive power limitation due to wind-farm collector networks

Type-3 and Type-4 wind turbines are capable of contributing to the reactive power required by wind-farms for supporting grid voltages. However, characterizing the maximum reactive power capability of a wind-farm by summing the individual generator ratings does not account for the effects of voltage variations over the radial collector network and can significantly overestimate the total reactive power production capacity. This paper considers the reactive power produced by a wind-farm in response to a common reactive power set-point Qset that is broadcast to all wind turbines. Analysis shows that a sustained increase in Qset will result in the wind-farm delivering maximal reactive power. Several examples demonstrate that generator voltage limits can significantly curtail the reactive power output requested by the control strategy. This improved characterization of wind-farm reactive power production capabilities, which takes into account collector network voltages, will enable better design and operation of wind-farm reactive power resources, reducing the need for additional shunt capacitors and static synchronous compensators.