Diagnosis of stator high-resistance connections in Wound Rotor Induction Machines for WECS

Design of modern Wind Energy Conversion Systems (WECSs) must take into account two crucial aspects: efficient control strategies and reliable monitoring and diagnosis techniques. Wind turbine generators based on Wound Rotor Induction Machine (WRIM) is actually the preferred technology mainly because of the lower rating of the power converter connected to the rotor side. With the association of a back-to back converter on the rotor side a Stator-Flux-Oriented-Control (SFOC) system can be used to obtain a decoupled control of the active and reactive power on the stator side with high efficiency. Faults detection at incipient stage in this power-generation system is mandatory to prevent unscheduled downtimes. In this paper, a convenient time-frequency analysis of the rotor modulating signals is confirmed by experimental results. The proposed system is suitable to be easily embedded in the power-converter digital control system at very low cost.