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Simulation & Analysis of speed control of separately excited DC motor using PID controller

It is a presentation on Simulation & Analysis of speed control of separately excited DC motor using PID controller

OBJECTIVES
1.  Applying armature control method to control speed of separately excited dc motor using PID controller.
2.      Modeling of full control system of the DC motor.
3.      Matlab and simulink has been used for performance analysis of the control system.

BASIC IDEA

Equation of speed,
N = (V - IaRa)/ φ
Where
N  = Speed of the DC motor
V  = Armature voltage
Ia  = Armature current
Ra = Armature resistance
 φ  = Flux
CHARACTERISTICS OF DC MOTOR
This is a basic characteristic of the motor; it is a linear relationship and is used to calculate the no-load speed and the start-up torque of the motor.
CHARACTERISTICS OF DC MOTOR

Speed, torque and power characteristics of separately excited DC motor
Speed, torque and power characteristics of separately excited DC motor

PID CONTROLLER
PID CONTROLLER
The transfer function of the PID controller looks like the following:
The transfer function of the PID controller
 
Kp = Proportional gain
KI = Integral gain
KD = Derivative gain
EFFECTS OF INCREASING PARAMETERS
-->
Parameter
Rise Time
Overshoot
Settling Time
Steady state error
       Kp
Decrease
Increase
Small Change
Decrease
      Ki
Decrease
Increase
Increase
Eliminate
      Kd
Small Change
Decrease
Decrease
Small Change
Tachometer is a kind of sensor which is electromechanical devices that converts mechanical energy into electrical energy.
DC tachometer
Fig: DC tachometer
The induced voltage is given by
Vo=Ktac
1.      Vo is output voltage,
2.      ω is angular velocity,
3.      Ktac is proportional constant.
Separately excited DC motor
Separately excited DC motor
Ra: the armature resistance


La: the armature inductance
ia: the armature current
if: the field current
ea: the input voltage
eb: the back electromotive force (EMF)
Tm: the motor torque
ω: an angular velocity of rotor
J: rotating inertial measurement of motor bearing
B: a damping coefficient
Block diagram of separately excited DC motor
image
The transfer function of the DC motor
G(s) = Ω(s) / Ea(s) = KT / {(Ra + Las)(B + Js) + KbKT}
La can be neglected due to its small value in practice, then,
Ω(s) / Ea(s) = KT / {Ra (B + Js) + KbKT} = {(KT/RaB) + KbKT} / {1 + (RaJs/RaB) + KbKT}
ð  Ω(s) / Ea(s) = Km / (τs + 1)
Km = KT / (RaB + KbKT) – is a motor gain,
τ = (RaJ/RaB) + KbKT – is a motor time constant
Block diagram of control system for the DC motor
Block diagram of control system for the DC motor
The closed loop transfer function of DC motor speed control system expresses as follows
The closed loop transfer function of DC motor speed control system expresses as follows
Specification
Experimental separately excited DC motor
KT = 0.06 Nm/A
Kb = 0.06 Vs/rad
Jm = 6.2 x 10-4 Nms2/rad
ωmax = rad/s
Imax = 2 A
ωNL = rad/s
Pmax = 54 Watt
Ra = 1.2 Ω
Bm = 1 x 10-4 Nms/rad
Labvolt DC motor (model 8211-0A)
KT = 2.161 Nm/A
Kb = 2.161 Vs/rad
Jm = 0.47 Nms2/rad
ωmax =  = 101.108 rad/s
Imax = 1.5 A
ωNL =  = 111.051 rad/s
Pmax = 472.643 Watt
Ra = 30.467 Ω
Bm = 0.046 Nms/rad
Labvolt DC motor (model 8211-0A)
 
DC motor (Experimental)
DC motor (Experimental)
DC motor (Experimental)
DC motor (Experimental)
SIMULINK MODEL
Labvolt DC motor (8211-0A)
SIMULINK MODEL


Labvolt DC motor (8211-0A)

CONCLUSION
  1. Mainly armature voltage is varied where the field current, armature circuit resistance is kept constant.
  2. Suddenly applied mechanical load causes high armature current due to decrease of the EMF.
  3. When the torque developed by the motor is exactly equal to the torque imposed by the mechanical load, and then the speed will remain constant.
Submitted by SAMIR DAS and SURUPAM CHAND DEV at July, 2009
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