Brushless dc motor and controllers

Brushless dc motor and controllers - Chapter 6 Brushless...

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Chapter 6 Brushless motors and controllers The Application of brushless motors, of all types, is becoming of considerable im- port^ce to the designers of machine tools and robotic systems. This is largely due to the benefits that these types of motor bring to a system, particularly in im- provements in the reUability. If the term is used in its broadest sense, this clas- sification will include permanent-magnet motors, stepper motors, and alternating currant (a.c.) induction motors. This chapter is concerned with permanent-magnet brushless motors and their associated controllers; a.c. asynchronous induction mo- tors and stepper motors will be considered in Chapters 7 and 8, respectively. Within the market place, there appears to be a degree of confusion in the nam- ing df motors, with given constructions. To prevent confusion, the following mo- tors ^ d their associated controllers are considered in this chapter. • Permanent-magnet synchronous motors with a trapezoidal winding distribu- tion, commonly known as d.c. brushless motors. The associated controller consists of a conventional three-phase bridge, whose switching pattern is determined by a low-resolution rotor-position sensor. • Sinewave-wound permanent-magnet synchronous motors incorporate wind- ings with an approximately sinusoidal distribution which are supplied with sinusoidal currents. These motors are normally controlled by a version of vector control, which has considerable similarities with the method used to control the asynchronous induction motors discussed in Chapter 7. In or- der to achieve the required control resolution, these motors are fitted with a resolver or a similar high-resolution position transducer. • Linear brushless motors are making significant inroads to the drives market; based on conventional brushless technology, they made an ideal replacement for high performance applications that would have been previously based on leadscrews and ballscrews. As will be discussed, the operation of these permanent-magnet brushless mo- tors is totally dependent on their associated electronics; so as the reliability and 169
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170 Commutation devices Stator with windings pre-installed - ^ Rear earth magnets Rotor Figure 6.1. Key features of a frameless bnishless dc motor. availability of power electronic devices and specialist integrated circuits has im- proved over the last twenty years the number of applications has also increased. Due to these motors' high reliability and low-maintenance requirements, they are ideally suited to a wide range of applications including computer cooling fans and robotic drives. As with brushed motors, the bnishless motor can be obtained in a number of versions, not only in is electromagnetic characteristics as summarised above, but also in its mechanical construction. The motors can be supplied either as a conven- tional framed or a frameless motor. The general arrangements of frameless brush- less motors is shown in Figure 6.1. A three-phase stator winding is constructed in a similar fashion to that of an a.c. induction motor; it is wound to give a trapezoidal
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Brushless dc motor and controllers - Chapter 6 Brushless...

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