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speed control of dc motor using choppers

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raviteja thummala

on 7 January 2013

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Transcript of speed control of dc motor using choppers

Speed control of DC motor
using chopper Introduction Choppers DC Motor V f = If Rf +Lf (dIf/dt)
V a = Ia Ra +La (dIa/dt)+Eg speed control Field & Armature Equations W=(Va-IaRa)/KvIf =Va/KvIf Complete Layout For
DC Motor Speed Control The output speed is compared with the reference speed and error signal is fed to speed controller.
Controller output will vary whenever there is a difference in the reference speed and the speed feedback
The output of the speed controller is the control voltage Ec that controls the operation duty cycle of (here the converter used is a Chopper) converter
The output speed of motor is measured by Tacho-generator and since Tacho voltage will not be perfectly dc and will have some ripple. So, we require a filter with a gain to bring Tacho output back to controller level [ chopper introduction A chopper is a static power electronic device that converts
fixed dc input voltage to a variable dc output voltage.

The power semiconductor devices used for a chopper circuit can be force commutated thyristor, power BJT, MOSFET and IGBT.GTO based chopper are also used

These devices are generally represented by a switch. When the switch is off, no current can flow. Current flows through the load when switch is “on”. control strategies of chopper time ratio control chopper operation Vo= (Ton/ (Ton+Toff))*Vs
= (Ton/T)*Vs

Vo = f* Ton* Vs Design of Speed control of
DC motor current limit control const frequency variable frequency seperately exited dc motor • Separately Excited DC motor has field and armature winding with separate supply.
• The field windings of the dc motor are used to excite the field flux.
• Current in armature circuit is supplied to the rotor via brush and commutator segment for the mechanical work.
• The rotor torque is produced by interaction of field flux and armature current. Eg= KvWO speed can be controlled by varying

Field current ---above rated speed
Armature voltage--below rated speed W(s) / Va(s) = [KO/Ra] /JS(1+TaS) /[ 1 +(K²O² /Ra)/JS(1+TaS)]

After simplifying the above transfer equation we get::

W(s)/Va(s) = (1/Km)/((1 + STm)(1 + STa)) Closed loop system model for
speed control of dc motor / Development of high performance motor drives are very essential for industrial applications
A high performance motor drive system must have good dynamic speed command tracking and load regulating response
DC drives, because of their simplicity, ease of application, reliability and favorable cost have long been a backbone of industrial applications
Also D.C motors are controllable over a wide range of speeds by proper adjustment of the terminal voltage. const frequency variable frequency GTO
Gate TurnOff Thyristor A GTO (Gate Turn Off) is a more versatile power-semiconductor device.
It is like a Conventional Thyristor but with some added features
The GTO can be turned-on by a gate signal, and can be turned-off by a gate signal of negative polarity Controller current controller design speed controller design A controller is used to keep the speed at the set-point value when, the set-point is ramping up or down at a defined rate
The controller used in a closed loop provides a very easy and common technique of keeping motor speed at any desired set-point speed under changing load conditions Types of controllers P PI PID Ia(s)(f)/Ia(s)ref={[Kc(1+TcS)/TcS](Kt)[(1/Ra)/(1+STa)}/{1+[Kc(1+TcS)/TcS
Kt[(1/Ra)/(1+STa)][K2/(1+T2S)]}

After simplifying the above transfer function we get:

Ia(S) (f) / Ia(S) (ref) = (1/K2)/ (2S²T2²2ST2+1) ωW(s)/W(s)(ref)= (Kn/K2)(Ra/KmTmTn)(1+TnS/(1+2T2S)S²)/{1+(Kn
Ra/K2KmTmTn)(1+TnS/(1+2T2S)S²)(K1/(1+T1S))}

After simplifying the above transfer function we get

(KnRa/K2KmTmTn)(1+T1S)/{K2KmTnS2(1+T1S)+KnRaK1} ωW(s)/W(s)(ref)= Ia(s) = (Va – KOW/ Ra(1+ LaS/Ra )
ωW(s)= (Td - TL )/JS
= (KOIa- TL ) /JS / / / / Future Prospects Fuzzy controller ?
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