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The universal motor is a rotating electric machine similar to a
DC motor but designed to operate either from direct current or single-phase
alternating current. The stator and rotor windings of the motor
are connected in series through the rotor commutator. Therefore
the universal motor is also known as an AC series motor or an AC
commutator motor. The universal motor can be controlled either as
a phase-angle drive or as a chopper drive.
In the phase-angle application, the phase-angle control technique
is used to adjust the voltage applied to the motor. A phase shift
of the gate's pulses allows the effective voltage, seen by the motor,
to be varied. The phase-angle drive requires just a triac.
In the chopper application, the Pulse Width Modulation (PWM) technique
is used to adjust the voltage applied to the motor. Modulation of
the PWM duty cycle allows the effective voltage, seen by the motor,
to be varied. Compared to a phase-angle drive, a chopper drive requires
a more complicated power stage with an input rectifier, a power
switch and a fast power diode. The advantage is higher efficiency,
less acoustic noise and better EMC behavior. |
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