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These motors are losing popularity to brushless motors. The brushes are subject to

continuous actuators -24.5

wear, which increases maintenance costs. In addition, the use of brushes increases resistance, and lowers the motors efficiency.

Figure 24.4 Pulse Width Modulation (PWM) For Control

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Figure 24.5 PWM Unidirectional Motor Control Circuit

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Figure 24.6 PWM Bidirectional Motor Control Circuit

24.2.2 AC Motors

o Power is normally generated as 3-phase AC, so using this increases the efficiency of electrical drives.
o • In AC motors the AC current is used to create changing fields in the motor.
* Typically AC motors have windings on the stator with multiple poles. Each pole is a pair of windings. As the AC current reverses, the magnetic field in the rotor appears to rotate.

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Figure 24.7 A 2 Pole Single Phase AC Motor

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L2

Figure 24.8 A 6 Pole 3-Phase AC Motor

* The number of windings (poles) can be an integer multiple of the number of phases of power. More poles results in a lower rotation of the motor.
o Rotor types for induction motors are listed below.

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