Methods for cogging torque reduction of directly driven PM wind generators

Finite Element Method Investigation and Loss Estimation of a Permanent Magnet Synchronous Generator Feeding a Non-Linear Load

“…Indeed, the amplitude of the higher harmonic components of the current is lower when magnets are placed asymmetrically, Figure 7a. According to [13,28,29], when the magnets are placed asymmetrically on the rotor there is a reduction in the cogging torque and also an EMF with lower harmonic distortion is induced. The cogging torque is the result of the interaction between the stator slot openings with the PMs on the rotor, so the period of the cogging torque is linked with the number of slots, Q, and poles, 2p.…”

“…The study uses two models, an analytical model and a FEA model, in order to simulate the generator while both the power electronics and the DC link voltage control are simulated by Simplorer. However, as stated in [5], although this co-simulation enables the researchers to investigate the full wind system, there is a waste of simulation speed due to the communication and synchronization subroutines, additional distances between the magnets, in order a more sinusoidal voltage waveform to be induced [13]. For comparison purposes both the asymmetric and the symmetric model were simulated.…”

“…Consequently, the FEA model of the PMSG can The investigated generator, that is a real commercial machine [11,12] with 12 slots, four pole pairs, 200 Hz nominal frequency, 660 W rated power, 48 V nominal voltage and 3000 rpm nominal speed, has been simulated. The stator winding is star connected, single layer, concentrated and non-overlapping, while the magnets are mounted on the rotor in an asymmetrical way, that is different distances between the magnets, in order a more sinusoidal voltage waveform to be induced [13]. For comparison purposes both the asymmetric and the symmetric model were simulated.…”

Study of an Outer-Rotor PMSG for use in Small Wind Applications

“…Cogging torque, is the result of the interaction (magnetic attraction) between the magnetic flux from the magnets and stator geometry, producing a variable reluctance related with the angular position of the rotor. This torque, overlaps the generator load torque causing not only stress and vibration, but also an absence of power delivery at small wind speeds [6]. Cogging torque can be expressed mathematically by the following equation [7], [8]:…”

“…Several methods [6][7][8][9][10] have been proposed to reduce cogging torque, in the case of the machine studied, this has the stator slots skewed, which requires, for its proper study, to use a more accurated model than the 2D model. Figure 4 shows cogging torque calculated from the full model (FLUX-SKEW) and taking into account the slot inclination.…”