Analysis of 3-Phase Short-Circuit and Demagnetization Characteristics in Direct-Drive SPM Wind Power Generators Considering Rotor Eddy Currents

In direct-drive surface-mounted permanent magnet synchronous generators (DD-SPMSGs), the rotor eddy current effect usually cannot be neglected due to solid rotor back iron. This paper first investigates the influence of rotor eddy currents on three-phase short-circuit (3PSC) peak currents and irreversible demagnetization. It is found that rotor eddy currents result in an increase in 3PSC phase peak currents. However, the shielding effect of rotor eddy current mitigates the demagnetization. In addition, the rotor core eddy currents contribute more to diminishing demagnetization compared to permanent magnets (PMs). Secondly, this paper analyzes post-demagnetization eddy current losses under 3PSC. It shows although the demagnetization distribution is uneven, the harmonic content of airgap flux density does not change. Furthermore, since the amplitudes of main harmonics decrease after demagnetization, the eddy current losses are reduced. In addition, as the overall demagnetization level increases, the alleviation of demagnetization due to rotor eddy current and the reduction of eddy current loss due to demagnetization become more obvious.