Basic brushless DC Motor
However, if, at the appropriate time, current is shut off in winding “R”, and turned on in winding “S”, then the rotor continues to move. Again at the appropriate time, shut off “S” and turned on “T”. By continuation of this timing sequence, complete rotation occurs. What is occurring, is that the field set up by the stator is being switched, and the rotor tries to catch up to it.
In this example, the explanation was simplified by exciting only one winding at a time. In reality, the stator consists of a three phase Y–connected winding, and two or three windings are actually energized.. This makes efficient use of windings and development of higher motor torques.
Basic Brushless Motor Basics
In its simplest form, a brushless dc motor consists of a permanent magnet, which rotates (the rotor), surrounded by three equally spaced windings, which are fixed (the stator). Current flow in each winding produces a magnetic field vector, which sums with the fields from the other windings. By controlling currents in the three windings, a magnetic field of arbitrary direction and magnitude can be produced by the stator. Torque is then produced by the attraction or repulsion between this net stator field and the magnetic field of the rotor.
Basic Brushless DC Motors
Conventional dc motors are highly efficient and their characteristics make them suitable for use as servomotors. However, their only drawback is that they need a commutator and brushes which are subject to wear and require maintenance. When the functions of commutator and brushes were implemented by solid-state switches, maintenance-free motors were realised. These motors are now known as brushless dc motors. In this chapter, the basic structures, drive circuits, fundamental principles, steady state characteristics, and applications of brushless dc motors will be discussed.
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