356 Ë 9 HTS Maglev bearing and flywheel energy storage system
or 1500 V DC. To satisfy the voltage, the HTS FESS units will be arrayed in series.
Furthermore, a DC-DC voltage converter must be introduced for each HTS FESS unit
to stabilize the output voltage because the output voltage of a PM synchronous motor
will decrease with the decrease of the rotation speed during the discharge process.
9.5.5PM assistant bearing
A PM assistant Maglev bearing was designed for the compensation of lateral stiffness.
The outer and inner diameters of the PM ring of bearing stator were 148 and 128 mm,
respectively. The outer and inner diameters of the PM ring of the bearing rotor were
120 and 100 mm, respectively. All of the PM rings used had a magnetic energy product
of 50 MGOe (398 kJ/m^3 ). The stator and rotor of the PM bearing were both composed
of eight pieces of PM ring. The calculated maximal axial and radial stiffness of the PM
bearing were about 1300 and 640 N/mm, respectively.
9.5.6Customized machining equipment
The YBCO bulks must have an arc surface to make up the entire stator of a HTS Maglev
bearing. For the YBCO bulk at 293 K, the Vickers hardness and the fracture toughness
is about 5.2±0.5 GPa and 1.3 MPa⋅m1/2, respectively, which means the YBCO bulk is
a hard and brittle material [80]. J. S. Wang et al. have designed and manufactured
customized equipment to machine the arc surface on the YBCO bulk. This customized
equipment is composed of three servo motors, which are controlled by programmed
logic controller (PLC) modules, as shown in Figs. 9.23 and 9.24. A grinding wheel is
fixed on the vertical servo motor, which supplies the grinding forces for the surface
machining of the HTS bulk. The HTS bulk will be fixed on a specially designed fixture
and be driven by the horizontal servo motors. The horizontal servo motors can move
in two directions separately.
The routes of the servo motors can be set by the operation staff through the PLC
modules. Thus, the YBCO bulk can be machined automatically. During the machining
Fig. 9.23:Customized equipment to machine the
surface of HTS bulk.