Categories DC Motor Machine

Speed Control Of DC Motor (Shunt, Series And Compound)

Mostly we want to control the speed of a DC motor on demand. This intentional change of drive speed is known as speed control of dc motor.

Speed control of a Direct current motor is either done manually by the operator or by means of an automatic control device. This is different from speed regulation – where the speed is trying to be maintained against the natural change in speed due to a change in the load on the shaft.

SPEED CONTROL OF DC MOTOR

The relationship given below gives the speed control of dc motor,

speed control of dc motor

Therefore, the speed of the 3 types of DC motors – shunt, series, and compound – can be controlled by changing the quantities on the right-hand side of the equation above.

Hence the speed can be varied by changing

  • Resistance control or Rheostat control.
  • Field flux φ Variation. This method is called field flux control.
  • Applied voltage variation. Another name of this method is armature voltage control.

 

1.ARMATURE RESISTANCE CONTROL

speed control of dc motor

Fig: (a) Speed control of a d.c. Shunt motor by armature resistance control.
(b) Speed control of a D.C. Series motor by armature resistance control.

In this system, a variable series resistor Re is put in the armature circuit. The figure (a), connection for a shunt motor above shows the process. In this case, the field is directly connected across the supply and therefore the flux Ф is not affected by the variation of Re.

Figure (b), D.C. series motor shows the method of connection of external resistance Re in the armature circuit.  In this term, the current and hence the flux φ is affected by the variation of the armature circuit resistance.

The voltage drop in Re minimizes the voltage applied to the armature, and therefore the speed is reduced.

This method has the following drawbacks:

  • In the external resistance Re a huge amount of power is wasted.
  • Control is limited to give speed below normal and an increase of speed cannot is obtained by this method.
  • For a conferred value of Re, the speed reduction is not constant but varies with the motor load.

This method is only used for small motors.

2.FIELD FLUX CONTROLφ

Since the field current produces the flux, and if we control the field current then the speed can be controlled. In the shunt motor, speed can be controlled by conjunctive a variable resistor Rc in series with the shunt field winding. In the diagram below resistor, variable resistor Rc is called the shunt field regulator.

speed control of dc motor

Fig:(a) Speed control of a D.C. shunt motor by variation of field flux.
(b) The diverter in parallel with the series of D.C. Motor.

speed control of dc motor , Gives the Shunt Field Current

Any of the one systems can vary the field current of the series motor:

  1. A variable resistance Rd is connected in parallel with the series field winding. The resistor connected in parallel is called the diverter. A portion of the main current is diverted through Rd.
  2. The second method uses a tapped field control.

Here the ampere-turns are varied by varying the number of field turns. This arrangement is used in electric traction.

speed control of dc motor

Figure: Tapped series field on D.C. motor

The advantages of field control are as follows:

  1. This is an easy and convenient method.
  2. The power loss in the shunt field is small because the shunt field current Ish is very small.

3.ARMATURE VOLTAGE CONTROL

We can control the speed of the D.C. motors by varying the armature of the applied voltage. The Ward-Leonard system of speed control works on these rules of armature voltage control. In this system, M is the main dc motor whose speed is to be controlled, and G is a separately excited dc generator. The generator G is driven by a three-phase driving motor which may be an induction motor or asynchronous motor. The combination of ac driving motor and the dc generator is also called the motor-generator (M-G) set.

speed control of dc motor

Figure: Ward-Leonard drive

ADVANTAGES OF WARD-LEONARD DRIVES:

  • This drive has a soft speed control of dc motor over a wide range in both directions.
  • It has an inherent regenerative braking capacity.
  • By using an overexcited synchronous motor as the drive for the dc generator, the lagging reactive volt-amperes of the plant are compensated. Therefore the overall power factor of the plant improves.

 

D.C MOTOR SPEED CONTROL THEORY:

To find the speed control of dc motor we start with the equation for the DC motor’s EMF. We know that the Electromagnetic force equation of DC motor is equal to:

speed control of dc motor

Hence rearranging the equation:

  • N = 60A E / PZØ

With k = PZ/60A, then:

  • N = E / kØ

Hence with E = V – IaRa, we derive the speed of the DC motor (N):

speed control of dc motor

Owner Of ICEEET

Summary
Speed Control Of DC Motor (Shunt, Series And Compound)
Article Name
Speed Control Of DC Motor (Shunt, Series And Compound)
Description
This intentional change of drive speed is known as speed control of dc motor.Speed control of a DC motor is either done manually by the operator.......
Author
Publisher Name
Habib
Publisher Logo

11 comments

If you are going for most excellent contents like me, just visit this site every day for the reason that it presents feature contents, thanks|

Wow, superb weblog format! How lengthy have you ever been running a blog for? you make blogging glance easy. The whole glance of your site is fantastic, let alone the content material!

[…] MOSFETs are switched at certain intervals of time for producing a three-phase supply to control the speed of the motor. This circuit also gives a light indication of any fault that occurs in the control […]

essay

Speed Control Of DC Motor (Shunt, Series And Compound) –

You actually make it appear really easy togwther with your
presentation but I to find this matter to be actually somehing that I believe I might never understand.
It sort of feels too comppex aand extremely broad for me.
I am havkng a look ahead to your subsequent submit, I will try to get the
hold of it!
https://californiaessay.wordpress.com/benefits-from-ordering-a-custom-essay
Good value Essay Composing Support 24\7,Personalized Admissions Essay 2014 Ordering a paper for reasonable.

esssay paperr writing service
essay papr writing service https://germaynelnovhwnp.medium.com/how-to-begin-a-scholarship-essay-ded378536d87

Leave a Reply

Your email address will not be published. Required fields are marked *