Курсовая работа: Planning of mobile complete set for a rural wind generator
3.6.3 Rotor Diameter (D)
The rotor diameter must be greater than the rotor yoke height (Hry ), shaft radius (Rshaft ) and the radial magnet length (Lm ) [10] .
D = 2 Hry + 2 Rshaft + 2Lm (Eq. 3.8)
In this design, D is restricted by the magnet arc radius of 25mm. Therefore D will be 50mm.
3.6.4 Rotor and Stator Yoke heights
The minimum rotor yoke height Hry is the same as the stator yoke height Hsy . The height should be large enough to avoid saturation. This also has advantages of reducing core loss and reluctance.
The minimum yoke heights are given by [10] :
(Eq. 3.9)
3.6.5 Airgap Length
The airgap length has a minimum value limited by the manufacturing tolerances; this value is typically in the range of 0.3mm to 1mm. In this design 0.5mm is chosen to be the airgap length.
3.6.6 Generator Length
The generator length is estimated to be 95mm; this is approximated from flux required to give the output voltage of the generator.
3.6.7 Airgap Flux Per Pole
In a radial machine, the flux per pole is given by:
(Eq. 3.10)
where B is the average airgap flux density, D is the rotor inner diameter, L is the generator length, Kst is the lamination stacking factor and p is the pole pairs.
For this design the average flux density per pole Bgav is equal to the peak flux density Bg since the magnet arc is close to 180 degrees. Therefore the peak airgap flux is estimated to be 0.5T at the airgap and Kst is assumed to be 0.97.
The airgap flux and the lamination stacking factors were estimated from the following dimensions of the loudspeaker magnet:
· Magnet arc = 180 mechanical degrees
· Inner radius = 8mm
· Arc radius = 25mm
· Magnet radial length = 4mm
· Area of one pole = 706.8 μm2
From the above magnet dimensions, the flux per pole in the machine is then estimated to be 1.16 mWb this value is calculated from equation 3.10.
3.6.8 Windings
The stators of most synchronous generators are wound with three distinct and independent windings to generate three-phase power [14] . A simple layer winding was used in this design. Slot per pole per phase was chosen to be 1 and the winding pitch was full pitch.
A. Types of winding
The preferred type of winding is distributed winding as it reduces harmonics and makes better use of the stator or rotor structure. The mmf induced in the airgap is not sinusoidal, to get a pure sinusoidal mmf the number of slots have to be infinity. This means that the distributed winding is expected to have some harmonics.
Induced voltage for the distributed windings is: