Coupling Effect on Unbalanced Voltages and Power Under Faulty Condition in Triple Three-Phase Wind Power Generators

In wind power generation, generators with multiple independent three-phase winding sets grow in popularity owing to their fault-tolerant capability. Nevertheless, when one three-phase channel malfunctions and is disconnected, it is found in this article that unbalanced voltages and output power occur under such a faulty condition in triple three-phase (TTP) generators. The reason is revealed to be the magnetic coupling between winding sets (WSs). By analogy with the transformer effect, an equivalent circuit model is built to investigate the coupling effect. Furthermore, the influence of factors such as the current angle, electric loading, and mutual inductances are discussed. When all three WSs operate, the currents of each WS can be regarded as shifted by a leading and lagging angle, respectively. Due to symmetry, these two effects cancel out in healthy operation. However, under faulty condition, only the leading effect still exists for one WS and the lagging effect for the other WS, resulting in the stated imbalance. Finally, experiments on a TTP machine validate the theoretical analysis.