Wind Turbine Negative Sequence Current Control and its Effect on Power System Protection

This paper focuses on the control of the negative sequence component of the wind turbine (WT) short circuit current. In many applications the negative sequence component is suppressed partially or entirely. Full negative sequence current suppression control would reduce the line-to-line short circuit current to the level of the load current or even to zero, thus interfering with the proper functioning of the conventional protection devices. To overcome this problem, the extension of the existing grid code has been proposed, which would require WT to inject a clearly defined level of negative sequence current. The injected current will additionally reduce the negative sequence voltage and improve the voltage phase symmetry. However, negative sequence current injection will limit the control capability of the WT in the positive sequence. The effect of different control options has been demonstrated using simulation on a test network and conclusions deduced.