Analysis of Negative-Sequence Directional Element for Type-IV Wind Power Plants under Various Control Methodologies

Negative-sequence directional element operation depends on the magnitude and the phase angle of the negative-sequence current with respect to negative-sequence voltage. The directional element's operation and simplicity of settings lies in the representation of sources with the passive elements in the negative-sequence network diagram. This is not always true for Inverter Based Resources (IBR) with control schemes that vary from manufacturer to manufacturer. IBR offers specific fault current signature based on the control system and fault ride through (FRT) conditions defined in the control scheme. This paper expounds negative-sequence currents for traditional sources and how the negative-sequence directional element uses this behavior to decide the fault direction. Then, a Type IV wind power plant (WP) is modeled for three different control schemes developed in EMTP-RV, and the negative sequence directional element behavior for various unbalanced faults is analyzed. This paper shows the similarities of the negative-sequence current of the German grid code-based control scheme with traditional sources during unbalanced faults. Recommendations are then made in terms of additional requirements from the German grid code and/or from the negative-sequence directional element logic to achieve improved dependability and security of the directional element.