Abstract:
The design of a high torque brush less DC moto rto replace the induction motor and worm gear for valve
actuators is described. Minimum motor cost, short axial
length and low electronics rating are achieved by selection of
open slots and coils wound on bobbins. First and second
harmonic designs are compared, with either 2 or 4 magnet
ales facing 3 teeth. As well as being cheaper from having
fewer coils, the second harmonic design is found to be superior
in having lower copper loss at peak torque. The peak
tangential force density across the gap was 5.8 x 104 N/m2.
Measurements are reported on 75 Nm and 150 Nm peak
torque prototypes, which are intended to "run" at 180 rpm
and at 20 Nm and 40 Nm respectively. Though 36 pole motors,
their no load loss would be sufficiently low for higher
speed operation, even to around 2000 rpm. Successful operation
as an actuator was observed on a valve.
