Addressing protection challenges associated with Type 3 and Type 4 wind turbine generators

Variable-speed doubly fed asynchronous (Type 3) and full converter-based (Type 4) wind turbine generators (WTGs) have complex fault current characteristics governed by proprietary controls. The control technique of some manufacturers is to produce balanced three-phase fault current during unbalanced faults. At present, short-circuit analysis tools commonly used by protection engineers are inadequate in representing the fault current behavior of these WTGs. This paper presents the fault current characteristics of a Type 4 WTG using a detailed MATLAB^® and Simulink^® model that incorporates pseudo control logic for this converter type. This paper also presents a case study of a misoperation of directional overcurrent relays connected to the collector circuit in an actual wind power plant during a fault. The paper provides recommendations on protecting wind power plants with these converter-based WTGs.