Motor Sizing
For high torque motor its better to use higher diameter
which gives more room for magnet around the rotor
As motor dimension is fixed, air gap flux density and ampere
turns are responsible for maximising the torque output
Low cost motor airgap shear stress varies
from 0.5 to 2
High cost motor airgap shear stress
varies from 1.5 to 3
Very high-performance motor airgap shear
stress varies from 2 to 10
Large liquid cooled machines airgap shear
stress varies from 10 to 20
Fundamental Implication
Power is directly proportional to
torque
Volume, mass, inertia is few constrains
we need to consider while designing
The volume of the motor increases
with square of radius or diameter
The ratio of output power to volume
cannot be increases by increasing motor diameter
Once diameter is chosen there are
two ways to increase power developed. First is by increasing the operating
speed. If speed is dictated by application, we need to use some form of speed
reduction to increase torque
Other way to increase power output
is by increasing magnetic and electrical loading.
Magnetic loading can be increased
by using high performance magnet
Surface mount machines and Interior
permanent magnet machines
Surface mount machines – low speed
operation, less complexity
IPM used for three reasons
- Flux concentration
- Rotor structural strength increases – high speed
- Drive over wide speed range – field weakening mode
