Electromagnetic Study of Direct-Driven Wind Turbine Generators by Coupled Field-Circuit Simulations and Full-Scale Bench Tests

Studying the electromagnetic behavior of gearless wind turbines, related to parasitic excitation of vibrations and audible noise emission, comes to the fore of science. Reliable simulation and testing methods are essential in this context. The electrical drive train, consisting of the generator that is coupled to a full-scale converter in modern direct-driven turbines, is the first component in the electrical energy supply chain. Particularly, the modeling of its interaction is focused on to study the harmonic content of the generator currents and excited forces in the air gap. Therefore, a weak numerical field-coupling method is used in this contribution to consider both, the current waveform resulting from the coupling and the magnetic forces computed by Finite Element Analyses (FEA). Measurement data, that is collected by means of a 4MW full-scale test rig, is considered to motivate and validate the proposed model approach. Moreover, the anomalous electromagnetic design of the considered generator is studied by the field-circuit simulation and corresponding magnetic air gap force harmonics are analyzed.