Pi controller ieee format

95
Design of Pi Controller To Minimize The Speed
Error of D.C. Servo Motor
Abstract— This study present efficient method for speed control of a D.C. Servo Motor using PI
controller. Design of a PI controller requires minimizing the error. The experimental is used to obtain
the transfer function to design the PI controller. The effectiveness of the design is validated using
MATLAB/Simulink. This new design method gives us a simple and powerful way to design a speed
controller for a servo – motor. This paper identifies and describes the design choices related to a PI
controller for a D.C. servo motor. D.C. servo motor is also variable speed drive, and paper presents
variable speed with minimizing speed error.
Index Terms— Control System, Proportional-Integral (P-I) controller, Speed control of d.c motor.
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INTRODUCTION
Everyone recognizes the vital role played by
electrical motors in the development of industrial
systems. There are five major
types of D.C motors in general use, which are the
separately excited D.C motor, the shunt D.C
motor, the permanent –
magnet D. motor, the series D.C motor and the
compound D.C
motor. The D.C machine is the first practical device
to convert electrical power into mechanical power,
and vice versa. Inherently straightforward operating
characteristics, flexible performance and efficiency
encouraged the use of D.C motors in many types
of industrial drive application. Most multi-purpose
production machines benefit from
adjustable speed control, since frequently their
speeds must change to optimize the machine process
or adapt it to various tasks for improved product
quality, production speed. The Proportional-
Integral (P-I) controller is one of the conventional
controllers and it has been widely used for the speed
control of dc motor drives [3]. The major features
of the P-I controller are its ability to maintain a
zero steady-state error to a step change in
reference. Due to sudden change in load torque and
the sensitivity to controller gains KR IR
and KRPR have been proposed for the
speed control of dc motors [8].
2 LITERATURE REVIEW
2.1 Servo Motor Description
Electric motors can be classified by their functions
as servomotors, gear motors, and so forth, and by
their electrical configurations as DC (direct
current) and AC (alternating current motors.
Servomotor is a motor used for position or speed
control in closed loop control systems. The
requirement from a servomotor is to turnover a wide
range of speeds and also to perform position and
speed. DC servo motors have been used generally
at the computers, numeric control machines,
industrial equipments, weapon industry, and speed
control of alternators, control mechanism of full
automatic regulators as the first starter, starting
systems quickly and correctly [4] [6]. Some
properties of DC servo motors are the same, like
inertia, physical structure, shaft resonance and
shaft characteristics, their electrical and physical
constants are variable. The velocity and position
tolerance of servo motors which are used at the
control systems are nearly the same. It has
implemented proportional integral, fuzzy logic
and adaptive neuro fuzzy inference system
respectively at the variable working situations to the
simulation model which has prepared at the
Matlab programmers for improvement the servo
motor performance.
2.2 Proportional plus Integral Controller
Description Proportional plus Integral (PI)
controllers are widely used in industrial practice
for more than 60 years. The development went
from pneumatic through analogue to digital
controllers, but the control algorithm is in fact the
same. The PI controller is standard and proved
solution for the most industrial application. The
main reason is its relatively simple structure, which
can be easily understood and implemented in
practice, and that many sophisticated control
strategies, such as model predictive control, are
based on it. An application with large speed
capabilities requires different PI gains than
an application which operates at a fixed speed.
In addition, industrial equipment that are
operating over wide range of speeds, requires

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different gains at the lower and higher end of the
speed range in order to avoid overshoots and
oscillations. Generally, tuning the proportional and
integral constants for a large speed control process
is costly and time consuming. The task is further
complicated when incorrect PI constants are
sometimes entered due the lack of
understanding of the process. The control action
of a proportional plus integral controller is
defined as by following equation.
E(t)U(t)=Kpe(t)+Kie(t)
Where:
u(t) is actuating signal.
e(t) is error signal.
Kp is Proportional gain constant.
Ki is Integral gain constant.
The Laplace transform of the actuating signal
incorporating in proportional plus integral control is
E(s)/U(s)=KpE(s)+KiE(S
The block diagram of closed loop control
system with PI control of D.C. Servo Motor
System is shown in Figure 3.1. The error signal
E(s) is fed into two controllers, i.e.
Proportional block and Integral block, called PI
controller. The output of PI controller, U(s), is
fed to D.C. Servo Motor System. The overall
output of D.C. drive, may be speed or position, C(s)
is feedback to reference input R(s). Error signal can
be remove by increasing the value of Kp , Ki .
Fig.1. Block diagram of PI Control Action with
D.C. Servo
Motor System
However the feedback of control system is unity.
If increases the gain of feedback the stability of
system is decreases.
3 MODELING OF D.C. SERVO MOTOR
3.1 Mathematical Modeling of D.C. Servo Motor
System
Fig.2. represented the servo motor model. Let’s
consider:-
Ea (t) =Input voltage
ia (t) =Armature current
Ra = Armature resistance
La = Armature inductance
Eb (t) =Back e.m.f
Tm = Developed Torque
ia (t) if
(t)
+
Ef
(t) Ea (t)
Eb
(t)
_
ωm
T
m
Fig.2. Separately Excited DC
Here, the differential equation of armature
circuitis

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Ea (t) =Ra .i a (t) + L a .di a (t) + Eb (t) (1)
dt
The Torque equation is-
Tm (t) = J.dωm (t) + B.ωm (t) (2)
dt
The torque developed by motor is proportional to the
product
of the armature current and field
current i.e.
Tm (t) = Kf .i f .i a (3)
Where, Kf is constant.
In armature – controlled D.C. motor the field current (i
f ) is kept constant i.e.
Tm = KT.i a (4)
Where, KT = Kf .if is torque constant.
The back e.m.f. of motor is proportional to the
speed i.e.
Eb (t) = Kb . ωm (5)
Where, Kb is back e.m.f. constant.
In order to create the block diagram of system initial
conditions are zero and Laplace transform is
implemented to the equations. i.e.
Ea (s) = Ra .Ia (s) + sLa .Ia
(s) + Eb (s)
Ia (s) = Ea (s) - Eb (s)
sLa +Ra
Tm (s) = sJ.ωm (s) + B.ωm (s)
ωm (s) = Tm (s)
(7)sJ + B
Tm (s) = KT.Ia (s)
(8)
Eb (s) = Kb . ωm (s)
(9)
The forward path blocks are the transfer function of
following:
Ia (s) = 1
Ea (s) - Eb (s) sLa + Ra
Tm (s) = KT
Ia (s)
ωm (s) = 1
Tm (s) sJ + B
The feedback path block is the transfer function of
following:
E b (s) = Kb
ωm (s)
Fig.3. only show the block diagram of armature
controlled.
4.1 D.C. Servo Motor Parameter
The motor used in this experiment is an 110V D.C.
motor with no load speed of 4050 rpm.
Parameter Value
R-resistance 0.6 Ω
L-inductance 8 mH
J-moment of inertia 0.0465 kg.m2
Kt -torque constant 0.052 Nm/A
Kb -electromotive force constant 0.1 V/rad/s
B-viscous friction coefficient 0.004 N.m/rad/s
d.c motor

98
4.1 Simulink
Model
Fig.4 shows the simulink model of D.C. Servo Motor
system. In this model two PI controllers is used. First
PI controller is used for control the speed and second
PI controller is use to control the armature current. The
speed response at different reference input 110V to
220V and 110V to 55V as shown in Fig.5 and Fig.7
respectively. And corresponding minimized speed error
as in Fig.6 and Fig.8.
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Fig.4. Simulink Model of D.C. Servo Motor
4.2 Responses
4.2.1 Speed Response (Ref. input 110V to
220V)
The speed response of D.C. servo motor is shown
below. The
rated reference input 110V for 5 second and then
suddenly increase input up to 220V for 4 second,
the corresponding speed is found. The value of
proportional gain and integral gain is adjusted to
minimized overshoots, rise time, peak time and
settling time. Due to minimization of transient
specifications the system becomes fast and steady
state easily occurs.
Fig.5. Speed Response of D.C. Servo Motor
4.2.2 Speed Error Response (Ref. input 110V to
220V)
The minimized seed error response at 110V to 220V
shown in Fig.6. From Fig.5 and Fig.6, when
reference input increase from 0V to 110V, the speed
error increase 0V to 110V. But when speed become
constant (become steady state) the error slightly fall
and become zero. When reference input increase from
110V to 220V, the speed error increase 0V to 110V.
But when speed become constant (become steady
state) the error slightly fall and become zero.
Fig.6. Speed Error of D.C. Servo Motor
4.2.3 Speed Response (Ref. input 110V to
55V)
The speed response of D.C. servo motor is shown
below. The rated reference input 110V for 5 second
and then suddenly decrease input up to 55V for 4
second, the corresponding speed is found. The value
of proportional gain and integral gain is adjusted to
minimized overshoots, rise time, peak time and
settling time. Due to minimization of transient
specifications the system becomes fast and steady
state easily occurs.
Fig.7. Speed Response of D.C. Servo Motor
4.2.4 Speed Error Response (Ref. input 110V
to 55V)
The minimized seed error response at 110V to 55V
shown in Fig.8. From Fig.7 and Fig.8, when
reference input increase from 0V to 110V, the speed
error increase 0V to 110V. But when speed become
constant (become steady state) the error slightly fall
and become zero. When reference input decrease from
110V to 55V, the speed error decrease from 0V to
55V. But when speed become constant (become steady
state) the error slightly increase and become zero.

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Fig.8. Speed Error of D.C. Servo Motor
CONCLUSI0N
A PI controller for a D.C. servomotor has been
studied. The performance of PI controller was
evaluated by simulation. The
controller gain was adjusted to obtain
minimized error
responses. The results show significant improvement
in maintaining performance of approximate zero
overshoot, minimum stabilizing time.
ACKNOWLEDGMENT
I feel a sense of deep self-satisfaction and a great
experience of having accomplished my paper
entitled “DESIGN OF PI
CONTROLLER TO MINIMIZE THE SPEED
ERROR OF D.C. SERVO MOTOR”.

Pi controller ieee format

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