Page 663 - Mechatronics with Experiments

ELECTRIC ACTUATORS: MOTOR AND DRIVE TECHNOLOGY 649
(a) Conventional DC motor

N S

_
+

(b) Inside-out DC motor

N
S

Reversing switch
_
+
(c) Brushless DC motor

N
S

Position
sensor

FIGURE 8.29: DC motor types:
Drive brush-type and brushless DC
motors.

PMDC motor, we have the same objective. However, the field magnetics is established by
the rotor and it rotates in space with the rotor. Therefore, the stator winding current has to
be controlled as a function of the rotor position so as to keep the stator generated magnetic
field always perpendicular relative to the magnetic field of the rotor, although both rotate in
space with the rotor speed. In other words, not only the magnitude of current in the stator
winding, but also the vector direction of it must be controlled. This switching of the currents
into the stator windings is achieved by controlling solid-state power transistors as a function