Page 190 - Electric Drives and Electromechanical Systems

184 Electric Drives and Electromechanical Systems

this design is very similar to that of the rotary motor (Wang et al., 2002). A linear motor
operates with a conventional d.c. brushless motor amplifier operating in the force,
instead of torque mode as used in rotary machines. As with any motor the use of a
position feedback to control position, velocity and acceleration is required.

6.4 Summary

This chapter has discussed the rotary BDCM and sinewave-wound motors. While the
application requirements will normally dictate which is the best option, a number of
comparisons can be drawn:

If the torque per r.m.s. ampere is compared using Eqs (6.6) and (6.22), for identical
peak motor fluxes, the torques of square-wave-wound motors exceed those of
sinewave-wound motors by a factor of 1.47. This effectively determines the relative
sizes between two motors with comparable characteristics.
The control systems for square-wave-wound brushless d.c. motors are considerably
simpler than those required for sinusoidally wound motors. BDCM only require
low-cost position encoders, whereas sinewave-wound motors require high-
precision systems.

While both types of motor give performances in excess of those of brushed motors,
they do so at a cost premium, which may be considerable. Brushless motors are being
more widely used as the cost of motors, and their essential electronics, continues to fall
as the technology matures, together advantages, including increased reliability and
reduction in maintenance. With the present technology, the performance is exceptional;
this has led to the introduction of electric drives in applications which have been the
preserve of hydraulics. However, as with all decisions of drive-system selection, the
additional complexity of these types of drives has to be balanced against their high
reliability and performance, it should be noted that brushless motors are widely used in
all forms of electric vehicles, while the power levels are greater than found in many
machine tool and related applications, the control principles are identical. It is expected
that more advanced control techniques will be developed as electric vehicle technology
moves forward.

References

Boldea, I., et al., 2018. Linear electric machines, drives, and MAGLEVs: an overview. IEEE Transactions
on Industrial Electronics 65 (9), 7504e7515. https://doi.org/10.1109/TIE.2017.2733492.
Gamazo-Real, J.C., Va ´zquez-Sa ´nchez, E., Go ´mez-Gil, J., 2010. Position and speed control of brushless dc
motors using sensorless techniques and application trends. Sensors 10 (7), 6901e6947. https://doi.
org/10.3390/s100706901.
Gieras, J., Piech, Z., Tomczuk, B., 2012. Linear Synchronous Motors. CRC Press, Boca Raton.