Answer / j.senthamizh

First we should be convert ac into dc using rectifier. Dc
motor speed control method classified into two 1.armature
control 2.field control . we are using armature control
method motor speed can be control below rated speed.or
using field control method the motor speed is above rated
speed. most people using armature control method because
field control method is dangerous than armature control
method.we are using field speed control at motor is running
condition and now field is open which times motor running at
dangerous speed. at the time motor bearing and shaft is
affected this condition.

Answer / saeid

I don't really understand why using field control can be
dangerous for a DC motor while this technique has been used
in thousands of application around the world without any
problem.

Any way, in order to control a DC motor, there are three
general ways: Armature voltage control
Field voltage control
Armature resistance control

Answer / sunil guru

one method can b used

firstly rectify the AC to DC then with the help of DC
chopper(DC-DC converter)convert 2 required voltage then to
provide that voltage 2 gate of MOSFET OR IGBT(full DC is
given 2 MOSFET ONLY CONTROLLED VOLTAGE IS GIVEN 2 GATE OF
MOSFET OR IGBT) and thus by giving the controlled voltage
to armature speed can be controlled

AND MOST COMMON 3 METHODS R THERE TO CONTROL SPEED OF DC
MOTOR

1.ARMATURE VOLTAGE CONTROL
2.FIELD FLUX CONTROL
3.ARMATURE RESISTANCE CONTROL

Answer / poorna

i think in all the above mentioned method there is a
disadvantage of motor reversal motor reversal cannot be
easily obtained we have to change the armature or feild
terminals, as magnetic field time const is much high field
reversal is not generally employed, even the reversal of
armature terminal is also not done as it may results in
jerks, so the best way is TO HAVE DUAL CONVERTER TO CONTROL
THE MOTOR IA ALL FOUR QUADRANTS

Answer / vidhy@....

By connecting a rectifier unit electrically, to an ac power
source to thereby supply a dc voltage to the dc motor drive
circuit;the rectifier unit is selected from the group
consisting of a bridge rectifier and a diode.
Further a voltage-stabilizing control unit,(u can
use a Metal-Oxide Semiconductor Field Effect Transistor for
this) electrically connected between the rectifier unit and
the dc motor drive circuit, and adapted to detect whether a
dc voltage supplied by the rectifier unit to the dc motor
drive circuit is a low dc voltage suitable for the
brushless dc motor; and

A voltage-stabilizing unit electrically connected
between the voltage-stabilizing control unit and the dc
motor drive circuit, said voltage-stabilizing unit being
controlled by the voltage-stabilizing control unit to
supply a stabilized dc voltage to the dc motor drive
circuit only if the voltage-stabilizing control unit
detects that the dc voltage supplied by the rectifier unit
is said low dc voltage;

wherein the dc voltage supplied from the rectifier unit is
passed through the voltage-stabilizing control unit
controlled by the voltage-stabilizing unit to turn on or
off the dc motor drive circuit, said voltage-stabilizing
control unit cutting off supply of dc voltage to the dc
motor drive circuit when a high dc voltage is detected.

Answer / a murthy

BY USING SUITABLE POWER ELECTRONIC CONTROLLERS LIKE
CONTOLED RECTIFIERS (BASED ON POWER RATING ) WE CAN CONROL

Answer / vilas

With help thyrister control drive,i.e. silicon controlled
rectfier.and tacho- generator for feed back and pot to
increase or decrease speed. ( to set speed).

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