Dynamic characteristics of large permanent magnet direct-drive generators considering electromagnetic–structural coupling effects

Dynamic characteristics of large permanent magnet direct-drive generators (PMDGs) considering electromagnetic–structural coupling effects are analyzed in this study. Using the conformal mapping method, the scalar magnetic potential of the air gap magnetic field considering the slot effect is calculated. On the basis of the discrete current element and magnetic equivalent circuit model, the local magnetic saturation effect of the stator and rotor is quantitatively simulated and the air gap magnetic field intensity distribution is obtained via numerical simulation. A series of uniformly distributed equivalent electromagnetic springs are introduced to develop an electromagnetic–structural coupling finite element PMDG model. The proposed air gap field analysis method is verified by the finite element analysis results. On the basis of the test platform for the Goldwind 1.5 MW PMDG, both modal and dynamic response tests for the stator/rotor coupling system are conducted, and the results are compared with the natural frequencies, mode shapes, and vibration responses obtained using the numerical model. The effects of the air gap length and rotor speed on the natural frequencies of the coupling system are analyzed. The proposed model has the potential to accurately evaluate the PMDG vibration energy, avoiding resonance points, and maintaining stable operations of the unit.