354 Ë 9 HTS Maglev bearing and flywheel energy storage system
Fig. 9.20:PM rotor of HTS Maglev bearing.of maximum strength of T-700. With the requirement of 5 kWh ESC, the calculated
outer diameter, inner diameter and height of the carbon flywheel rotor were 770 mm,
540 mm and 380 mm, respectively.
The shape of the flywheel hub was optimized and the comparison of stress is
shown in Fig. 9.21. From the results of Fig. 9.21, it is clear that the optimization
can reduce the maximal radial stress from 320 to 240 MPa, which is safe for most
aluminum alloys.
For an integral flywheel rotor, the eigen-frequencies are very important because
there may be serious vibration or deformation of the rotor. The first and second
calculated eigen-frequencies of the rotor are about 3.5× 10 −^4 and 3.4 Hz, respectively.
No serious distortion occurs at those two eigen-frequencies. The third eigen-frequency
is about 433.3 Hz, and it causes serious deformation, as shown in Fig. 9.22. Fortunately,
the eigen-frequency of 433.3 Hz, which equals a rotation speed of 25,998 rpm, is much
above the designed operation speed of 15,000 rpm for the flywheel rotor. However,
enough attention should be paid to the first and second eigen-frequency because of
Fig. 9.21:Optimal results for the flywheel hub. Stress-phi and stress-r represents the azimuthal and
axial stress, respectively.