Magnetic Field Sources - Magnetocaloric Energy Conversion: From Theory to Applications - page 82

Fig. 3.43 The magnet assembly, i with two halves of the magnet system in which the rotor or the
static part is shifted by 45 ° (only the shifted magnet is shown in the gure) (see also Bouchekara

et al. [ 56 ])

AMR bed was varying from 0.05 to 0.94 T). The results, however, revealed that the
reference magnet assembly is characterized by high mechanical stresses on both the
AMR beds and the driving actuator [ 56 ]. The authors also reported that the mag-
netic le of the reference magnet assembly was the most trapezoidal among

the selected cases, which should, according to Bouchekara et al. [ 56 ], ensure a
better magnetization and demagnetization cycle. As a negative consequence, the
cogging torque and forces were very high.
The total torque of the structure was de

eld pro

ned as the cogging torque acting on the
rotating bar magnet. This torque had the opposite value of the torque obtained on
the stator (poles). It varied sinusoidally with the magnet position and its maximum
value was about 20 Nm. The authors stated that the increase in the number of poles
can signi cantly decrease the magnetic torque; however, this would also lead to a

more complex device. It was also indicated by the authors that one of solutions to
overcome the problem of cogging torque was to apply a passive torque-compen-
sation system that represented the eight poles synchronous magnetic coupling,
designed to produce the same torque as the reference magnets, but with the opposite
phase. With this solution a reduction of 10 Nm was achieved.
Figure 3.43 shows another solution for the magnet assembly in which this
consists of two partial magnet systems (as the cascade) and in which the rotor
(magnet bar) or the static part are shifted by 45

° . These solutions were evaluated in

order to minimize the magnetic torque.
Based on numerical simulations, the following results were obtained and are
discussed in the subsequent text (see also the results in Table 3.1 ):

￿ The solution represented by the magnet assembly (c) with the smooth iron ring

led to a decrease of the total torque, and the reluctance variation was left due to
the MCE magnetic beds, which acted as additional poles. The maximum
magnetic flux density, compared to the reference magnets, was slightly lower.