This document analyzes the closed-loop speed control of a chopper-fed separately excited DC motor using PI controllers. It presents the modeling of a separately excited DC motor and discusses various controller types for DC motor speed control. The proposed system uses a buck converter/chopper to control the armature voltage and thereby the speed of the DC motor. PI controllers are used to generate PWM pulses for the chopper by comparing the reference and feedback speeds. Simulation and experimental results are presented to validate the closed-loop speed control using PI controllers for different load conditions.

1. CLOSED LOOP PERFORMANCE INVESTIGATION OF
CHOPPER FED DC MOTOR USING VARIOUS
CONTROLLER
1
M.Abinaya,2
P.Nedumal Pugazhenthi,3
S.Selvaperumal,4
G.Prabhakar,5
P.Gnana skandaparthiban
1
P.Gscholar,SyedAmmalEngineering College,Ramanathapuram, TN, INDIA
2
Associate Professor,syedammal Engineering college,Ramanathapuram,TN,INDIA
3
Professor, Syedammal Engineering college, Ramanathapuram,TN,INDIA
4
Assistant Professor,Syedammal Engineering college,Ramanathapuram,TN,INDIA
5
Assistant Professor,SyedAmmal Engineering college,Ramanathapuram,TN,INDIA
1
abinaya987@gmail.com,2
neduaupci@gmail.com,3
perumalvnr@gmail.com,4
gprabhakar2488@gmail.com,5
parthiban_est@gmail.com
Abstract
This paper analyse the study of closed loop performance
investigation of chopper fed separately excited dc motor using
PI controllers. Speed of separately excited DC motor can be
varied below and above the rated speed by various techniques.
Conventional controllers are commonly being used to control
the speed of the DC motors in various industrial applications.
It is to be found as a simple, robust and highly effective when
the load disturbance is small. The aim of this project is to
control this Speed of chopper based separately excited DC
motor. The PWM pulses are generated by the chopper to
control the motor speed.
The duty cycle of the PWM pulse are varied by PI
controller to attain the closed loop response. The chopper
firing circuit receives variable PWM pulses from PI
controller, to produces the variable voltage to the armature of
the motor for achieving desired speed response.
Keywords: separately excited DC motor,chopper,proportional
integral controller(PI),proportional integral derivative(PID).
I. Introduction
The development of high performance motor drives is very
important in industrial as well as other purpose applications
such as steel rolling mills, electric trains and robotics.
Generally, a high performance motor drive system must have
good dynamic speed command tracking and load regulating
response to perform task.DC drives are choosen because of
their simplicity,easiness of application, high reliability,
flexibility and less cost, this is the backbone for industrial
applications, and home appliances.wherethe speed and
position control of motor are required. DC drives are less
complex with a single power conversion from AC to DC.
Again the speed torque characteristics of DC motors are much
more superior to That of AC motors. A DC motors provide
excellent control of speed for acceleration and deceleration.
DC motors have a long tradition of use as adjustable speed
machines and a wide range of options have developed for this
purpose. In these applications, the motor should be precisely
controlled to give the desired performance. The controllers of
the speed that are conceived for goal to control the speed of
DC motor to execute one variety of tasks, is of several
conventional and numeric controller types, the controllers can
be: proportional integral (PI), proportional integral derivative
(PID) Fuzzy Logic Controller (FLC) or the combination
between them: Fuzzy-Neural Networks, Fuzzy Genetic
Algorithm, Fuzzy-Ants Colony, Fuzzy-Swarm[7].
The proportional – integral – derivative (PID) controller
operates the majority of the control system in the world. It has
been reported that more than 95% of the controllers in the
industrial process control applications are of PID type as no
other controller match the simplicity, clear functionality,
applicability and ease of use offered by the PID controller [3],
[4].
PID controllers provide robust and reliable performance for
most systems if the PID parameters are tuned properly. The
major problems in applying a conventional control algorithm
(PI, PD, PID) in a speed controller are the effects of non-
linearity in a DC motor. The nonlinear characteristics of a DC
motor such as saturation and fiction could degrade the
performance of conventional controllers [1], [2].
Generally, an accurate nonlinear model of an actual DC motor
is difficult to find and parameter obtained from systems
identification may be only approximated values. The field of
Fuzzy control has been making rapid progress in recent years.
Fuzzy logic control (FLC) is one of the most successful
applications of fuzzy set theory, introduced by L.A Zadeh in
1973 and applied (Mamdani 1974) in an attempt to control
system that are structurally difficult to model. Since then,
FLC has been an extremely active and fruitful research area
with many industrial applications reported [5].
In the last three decades, FLC has evolved as an alternative or
complementary to the conventional control strategies in
various engineering areas. Fuzzy control theory usually
provides non-linear controllers that are capable of performing
different complex non-linear control action, even for uncertain
nonlinear Systems. Unlike conventional control, designing a
FLC does not require precise knowledge of the system model
such as the poles and zeroes of the system transfer functions.
Imitating the way of human learning, the tracking error and
the rate change of the error are two crucial inputs for the
design of such a fuzzy control system [6], [7].
II.Proposed system
Armature voltage control method is used to vary the
speed of separately excited DC motor below and up to the
rated speed. (Fig.1) shows the block diagram of the proposed
method. The system consists of buck converter type DC–DC
power converter or chopper for driving the separately excited
DC motor. The performance of the DC drive will be based on
International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.55 (2015)
© Research India Publications; httpwww.ripublication.comijaer.htm
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2. the choice of controllers. The output speed of the motor is
compared with the reference speed and the error signal is fed
to speed controller. Whenever there is a difference between
the reference speed and the feedback speed, the controller
output will be changed. The output from the speed controller
is the control voltage Ec that provides required gating signals
to vary the duty cycle of the chopper circuit.The chopper
output give the required armature voltage to achieve the
desired speed response.
.
Fig1:Block diagram of proposed system.
III. MODELING OF SEPARATELY EXCITED DC MOTOR
Figure 2: Separately Excited DC motor
The armature equation is shown below:
The description for the notations used is given below:
TERMINOLOGY:
1. VA is the armature voltage in volts.
2. Eg is the motor back emf in volts.
3. Ia is the armature current in amperes.
4. Ra is the armature resistance in ohms.
5. La is the armature inductance in Henry.
Now the torque equation will be given by:
(2)
Where:
TL is load torque in Nm.
Td is the torque developed in Nm.
J is moment of inertia in kg/m².
B is friction coefficient of the motor.
ω is angular velocity in rad/sec.
In absence of friction in motor, it will give:
Therefore, new torque equation will be:
(3)
By Takingthe field flux as Φ and (Back EMF Constant)
Kv as K. Equation for back emf of motor will be:
(4)
Also,
(5)
After taking Laplace Transform on both sides, we will
get:
Now, taking equation (5) into consideration, we have:
And,
Also, The armature time constant is given by:
Figure 3: Block Model of Separately Excited DC Motor
After simplifying the motor modelFig 3, the overall transfer
function will be:
Further simplifying the above transfer function will get as:
(6)
Assuming, as time constant.
Then the above transfer function can be written as below:
(7)
When starting of motor, load torque TL = 0 and applying full
voltage Va
Also assuming negligible armature inductance, the basic
armature equation can be written as:
At the same time Torque equation will be:
(8)
Placing the value of Ia in above armature equation:
Dividing on both sides by KΦ,
(9)
-Va/KΦ is the value of motor speed under no load condition.
Therefore,
ω (no load)=
Where, (say)
And,
Therefore,
(10)
From motor torque equation, we have:
(11)
International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.55 (2015)
© Research India Publications; httpwww.ripublication.comijaer.htm
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3. From equation (5.10) and (5.11), we have:
Now, Replacing KΦ by Km in equation (5.7), we get:
(12)
Since, the armature time constant Ta is much less than the
electromechanical time constant Tm (Ta<< Tm) Simplifying,
The largest time constant will play major role in delaying the
system when the transfer function is in time constant. By
compensate the delay due to large time constant we use PI
controller as speed controller. It is because the zero of the PI
controller can be chosen in such a way that this large delay can
be cancelled. In Control system term a time delay
generallycorresponds to a lag and zero means a lead, so the PI
controller will try to compensate the whole system.
Hence, the equation can be written as:
(13)
Tm and Ta are the time constants of the above system transfer
function which will determine the response of the system.
Hence the dc motorcan be replaced by the transfer function
obtained in equation (13) in the DC drive model shown in Fig
3.
IV. HARDWARE DESCRIPTION
A. FUNDAMENTAL
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. This
controller can also be used to keep the speed at the set-point
value when, the set-point is ramping up or down at a defined
rate.
In this closed loop speed controller, a voltage signal
obtained from a Tacho-generator attached to the rotor which is
proportional to the motor speed is fed back to the input where
compared signal is with the set-point speed to produce an error
signal. This error signal is then fed to work out what the
magnitude of controller output will be to make the motor run
at the desired set-point speed. For example, if the error speed
is negative, this means the motor is running slow so that the
controller output should be increased and vice-versa. The dc
motor specification used in this hardware setup are,voltage
12V,current1A,speed14000rpm.
B.OPEN LOOPCIRCUIT DIAGRAM
Fig 4: Open loop circuit diagram
C .OPEN LOOP OPERATION
A 230v supply is provided to step down transformer to get
24v which is fed to the bridge rectifier circuit and which is
converted to AC to DC.The DC 24v voltage obtained from the
rectifier is fed to IC7812(+12v),this voltage regulator is used
to regulate the input to 12v and given again to
ic7805(+5v).this 7805 voltage regulator, here the +5v is
regulated from this voltage regulated. which is used for the
input voltage for 555 timer circuit, here the timer circuit is
generate the gate pulse which is used to drive the motor using
MOSFET.By changing the duty cycle the motor voltage is
modified and getting the desired speed is obtained.
D.OPEN LOOP HARDWARE SETUP
Fig 5: Open Loop Hardware Model
V. ANALOG PROPORTIONAL CONTROLLER CIRCUIT
DIAGRAM
Fig 6:Analog proportional controller circuit diagram
International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.55 (2015)
© Research India Publications; httpwww.ripublication.comijaer.htm
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4. VI. COMPARATIVE ANALYSIS FOR THEORITICAL AND
PRATICAL VALUES
Table 1: Comparative analysis for theoreticaland practical values
VII.COMPARSION OF OUTPUT VOLTAGE BETWEEN
PRATICAL AND THEORITICAL VALUE
Fig 7: Comparison of output voltage between theoretical
value and practical values
VIII. ANALOG PROPORTIONAL CONTOLLER
HARDWARE
MODEL
Fig 8.Analog Proportional Controllerhardware Model
XI.OUTPUT VOLTAGE FOR RA=3.3KΩ,RB=5KΩ ,C=0.01μF
Fig9: output voltage for resistor ra=3.3kΩ, rb=5kΩ, c=0.01μf
X.ANALOG CONTROLLER OPERATION
In analog PI controller the inversion input voltage
230v is converted into 24v using step down transformer. The
half diode bridge rectifier is used between the transformer and
regulator which is used to convert 24v AC to 24v DC. In PI
controller is consist of 6 operational amplifiers with specified
resistor with potential transformer. The gate pulse is produced
by 555 timer by using the voltage regulator 7805(+5v), and
here the IC is MOSFET chosen. Gate signal is given to
theMOSFET terminal the motor speed is controlled by
varying the potential transformer which is connected to the PI
controller.
XI. CONCLUSION
The speed of a dc motor has been successfully
controlled by using a Chopper as a converter and
Proportional-Integral type Speed and Current controller based
on closedloop system model. Initially a simplified closed loop
model for speed control of DC motor is considered and
requirement of current controller is studied.
The hardware setup is carry out in this project by varying
reference speed and by varying load are also obtained.
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International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.55 (2015)
© Research India Publications; httpwww.ripublication.comijaer.htm
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International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.55 (2015)
© Research India Publications; httpwww.ripublication.comijaer.htm
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