Implementation of Chopper Fed Speed Control of Separately Excited DC Motor Using PI Controller

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International Journal Of Engineering And Computer Science ISSN:2319-7242
Volume 6 Issue 3 March 2017, Page No. 20631-20633
Index Copernicus value (2015): 58.10 DOI: 10.18535/ijecs/v6i3.41
R.Nagarajan, IJECS Volume 6 Issue 3 March, 2017 Page No. 20629-20633 Page 20629
Implementation of Chopper Fed Speed Control of Separately Excited DC
Motor Using PI Controller
R.Nagarajan1, S.Sathishkumar2 S.Deepika3, G.Keerthana4, J.K.Kiruthika5, R.Nandhini6.
1Professor, Department of Electrical and Electronics Engineering, Gnanamani College of Technology, Namakkal, India.
Email-krnaga71@yahoo.com
2Asst. Professor, Department of Electrical and Electronics Engineering, Gnanamani College of Technology, Namakkal, India.
2-5 U.G. Students, Department of Electrical and Electronics Engineering, Gnanamani College of Technology, Namakkal, India.
Abstract: This paper presents a speed control of a separately excited DC motor by using PI (Proportional Integral). The speed of the
separately excited DC motor can be varied below and above the rated speed by various speed control techniques. It can be varied above the
rated speed by field flux control and below the rated speed by armature terminal voltage control. The conventional controllers are
commonly being used to control the speed of the DC motors in various industrial applications. It’s found to be simple, robust and highly
effective, when the load disturbance is small. Here, we using chopper as a converter the speed of DC motor is controllable. The chopper
firing circuit gets signal from controller and then by supplying variable voltage to the armature of the motor then to obtain the desired speed
of the motor. There are two different types of control loops, current controller and speed controller. The controller used is Proportional-
Integral type. The current and speed controller loop is designed and in order to get stable and high speed control of DC motor. The
simulation of the above model is done in MATLAB/SIMULING under varying speed and torque condition.
Keywords: Chopper circuit, DC motors, PI-controller, MATLAB (SIMULINK).
1. INTRODUCTION
An electrical drive system consists of electric motors,
power circuit, controller and energy transmitting shaft. In
modern electric drive system power electronic converters are
used as power controller. Electric drives are mainly of two
types: DC drives and AC drives. They differ from each other
in this way that the power supply in DC drives is provided by
DC motor and power supply in AC drives is provided by AC
motor [1]. The DC motors are used extensively in adjustable
speed drives and position control system. The speed of DC
motors can be adjusted by below the rated speed and above
the rated speed. Their speed below rated speed is controlled
by armature voltage [2]. The development of high
performance motor drives is very essential for industrial
applications. A high performance motor drive system must
have good dynamic speed command tracking and load
regulating response [3]. The DC drives are widely used in
applications requiring adjustable speed control, frequent
starting, good speed regulation, braking and reversing. Some
important applications are paper mills, rolling mills, mine
winders, hoists, printing presses, machine tools, traction,
textile mills, excavators and cranes.. For industrial
applications development of high performance motor drives
are very essential [4]. There are various types of speed
control techniques are available for DC drives, such as,
armature voltage control, field flux control and armature
resistance control.
For controlling the speed and current of DC motor, speed
and current controllers are used [5]. The main work of
controller is to minimize the error and the error is calculated
by comparing output value with the set point. This paper
mainly deals with controlling the DC motor speed using
chopper as power converter and PI as speed and current
controller [6]. Now days Induction motors, brushless DC
motors and synchronous motors have gained widespread use
in electric traction system. Hence Dc motors are always a
good option for advanced control algorithm because the
theory of DC motor speed control is known more than other
types. The speed control techniques in separately excited DC
motor, by varying the armature voltage for below rated speed
[7]. The power semiconductor devices used for a chopper
circuit can be force commutated thyristor, power BJT,
MOSFET, IGBT and GTO based chopper are used. It having
very low switching losses that means total voltage drop has
0.5V to 2.5V across them [8]. The various controllers that
can be used in speed control operation are available.
Proportional plus Integral (PI) is the most preferred
controller, which are designed to eliminate the need for
continuous operator attention thus provide automatic control
to the system [9].
II. CHOPPER
A chopper is a high speed on-off switch which converts
fixed DC input voltage to a variable DC output voltage. A
Chopper is considered as a DC equivalent of an AC
transformer as they behave in an identical manner. The
Figure.1 shows the basic chopper circuit, output voltage and
current waveform The choppers are more efficient as they
involve one stage conversion [10], [11].
Figure 1: Chopper circuit, voltage and current waveform.
Average Voltage,
Vo = (Ton/ (Ton+Toff))*Vs (1)
= (Ton/T)*Vs

DOI: 10.18535/ijecs/v6i3.41
R.Nagarajan, IJECS Volume 6 Issue 3 March, 2017 Page No. 20629-20633 Page 20630
= αVs
Ton = on-time.
Toff = off-time.
T = Ton + Toff = Chopping period.
α=Ton/T.
Hence, the voltage can be controlled by varying duty cycle
α.
III. BUCK CONVERTER
A chopper is a static power electronic device, which
converts fixed DC input voltage to a variable DC output
voltage. It can be step up or step down. It also considered as a
DC equivalent of an AC transformer since they behave in an
identical manner. Due to its one stage conversion, choppers are
more efficient and now being used all the world for rapid
transit system, in marine hoist, in trolley cars, in mine haulers
an in shift trucks etc., [12]..
The circuit diagram of traditional buck converter is
shown in Figure 2. It consists of constant input voltage (Vs).
The buck converter is connected between the supply and the
load. To maintain constant output voltage a capacitor is
connected to the load. The feedback is provided by the
controller connected to the output of the buck converter.
Figure2: Buck converter
The power semiconductor devices used for a
chopper circuit can be force commutated thyristor, BJT,
MOSFET, IGBT and GTO. These devices are generally
represented by a switch. When the switch is OFF, no current will
flow in the circuit. The current flows through the load when
switch is ON. The power semiconductor devices have ON-state
voltage drop of 0.5V to 2.5V across them. For the sake of
simplicity, this voltage drop across these devices is generally
neglected [13]. During period Ton, Chopper is ON and load
voltage is equal to source voltage Vs. During the interval Toff,
chopper is OFF, load current flows through the freewheeling
diode FD. As a result, load terminals are short circuited by FD
and load voltage is therefore, zero during Toff. During Ton, load
current rises whereas during Toff load current decays.
IV. SEPARATELY EXCITED DC MOTOR
Separately excited DC motor has field and armature
winding with separate supply voltage. Field winding supplies
field flux to armature. When DC voltage is applied to motor,
current is fed to the armature winding through brushes and
commutator. Since rotor is placed in magnetic field and it is
carrying current also. So motor will develops a back emf and a
torque to balance load torque at particular speed [14], [15].
Figure 3 shows the equivalent circuit of separately Exited DC
motor
Figure 3: Equivalent circuit of separately Exited DC motor
When a separately excited DC motor is excited by a field
current of and an armature current of flows in the circuit,
the motor develops a back EMF and a torque to balance the
load torque at a particular speed. The field current is
independent of the armature current . Each winding is
supplied separately. Any change in the armature current has no
effect on the field current. The is generally much less than
the . In the above figure suppose is the armature voltage
in volt, is the armature current in ampere, is the motor
back emf in volt, is the armature inductance in Henry, is
the armature resistance in ohm [16].
(A)PI CONTROLLER
The proportional and Integral controller produces
an output signal, u (t) proportional to both input signal, Vi (t)
and integral of the input signal, Vi (t) and is given by,
From the comparator the reference speed is compared with
the actual speed and an error signal is obtained and is given
to the PI control. By properly selecting the proportional gain
(Kp) and integral gain (Ki) the desired response can be
obtained. Once buck converter is injected with the speed
from the reference and the PI controller starts function, it
varies the value of the duty cycle which will change the input
value that is sensed by the PI controller [17]-[19].
Figure 4: PI controller with DC motor (PI)
The Figure 4 shows the proportional band of the
controller. The process of selecting controller parameter to
meet given performance specification is known as controller
tuning. Ziegler and Nichols suggested rules for tuning PI
controller (mean to set the values of Kp and Ki) based on the

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R.Nagarajan, IJECS Volume 6 Issue 3 March, 2017 Page No. 20629-20633 Page 20631
experimental step response or based on the value of Kp that
result is marginal stability, when only proportional control
action is used. Ziegler-Nichols rules, which are briefly
presented in the following, are useful when mathematical
models of plans are not known. These rules can, of course, be
applied to design of system with known mathematical models.
Such rules suggest a set of values of Kp and Ki that will give a
stable operation of the system. However, the resulting system
may exhibit a large maximum overshoot in step response,
which is unacceptable [20], [21]. In such a case, we need
series of fine tunings until an acceptable result is obtained. In
fact, the Ziegler-Nichols tuning rules give an educated guess
for parameter values and provide a starting point for fine
tuning, greater than giving the final settings for Kp and Ki in a
single shot.[22].
Table I: Comparison of gain response of three Controllers
Parameter
Speed of
Response
Stability
Accuracy
increasing P
Increase
Deteriorates
Improves
increasing PI
Decrease
Deteriorates
Improves
increasing PID
Increase
Improves
No
impact
TABLE II: Effects on output parameter of P, PI and PID
Controller
Parameter
P
Controller
PI
Controller
PID
Controller
Rise time
Decrease
Decrease
Minor
Decrease
Overshoot
Increase
Increase
Minor
Decrease
Settling
time
Small
change
Increase
Minor
Decrease
Steady state
error
Decrease
Significant
change
No change
Stability
Worse
Worse
Small Better.
Table 1 and 2 show the effects of coefficients and
effects of changing in control parameters of the controllers.
From the table, it is observed that, if decrease in rise time in
the P and PI controller, the overshoot will be increase and
there is no change in settling time, and also in steady state
error. The PI controller gives better result than P and PID
controller.
From the performance analysis, it is to be noted that,
when gain is increases the speed of response is increases in P
and PID controller, but in PI controller gain of response is
decreases. In PI controller there is a significant change in
various parameter and there is no change in steady state error
which can see from Table 1 and Table 2. So, PI controller is
better than P and PID controller. The P controller can
stabilize only in 1st order unstable process and PID
controller can be used only when dealing with higher order
capacitive processes but PI controller is applicable in all
stages. The comparative study of P, PI and PID Controller is
carried out, in which PI controller gives good response than
any other controller.
V. SIMULATION RESULTS
In Figure 5 shows the simulation model of basic
buck converter. In that model the MOSFET is used as a
switch for the best performance of voltage control, fast
switching and low losses. Here initially given input supply
voltage is 5V. In that supply voltage will be maintain the
constant output voltage in load resistance. There are three
buck converter parameters are monitoring by using displays.
When the MOSFET switch is closed supply voltage is
connected to load and the load current starts to increase.
When the MOSFET switch is opened, the freewheeling
diode to maintain the continuous current path in the load.
Figure 5: Simulation diagram of buck converter
Figure 6: Simulation results of buck converter (a) PWM,
(b) Input Voltage, (c) Output Voltage and (d) Load Current
The simulation circuit is necessary to get the output
waveform. In input side we are giving 12V that voltage is
getting in output side as 5.63V. The scope has four signals for
PWM, Input voltage, output voltage, load current are shown
in Figure 6(a), (b), (c) and (d).
In Figure 7 shows the simulation model of separately
excited DC motor with PI controller. In that model the
MOSFET is used as a switch for the best performance of
voltage control, fast switching and low losses. Here initially
given input supply voltage is 230V. In that supply voltage
will be maintain the required output voltage to the load. In
that PI controller output is act as the modulation index of the

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R.Nagarajan, IJECS Volume 6 Issue 3 March, 2017 Page No. 20629-20633 Page 20632
converter. The relational operator can be comparing the
reference signal to the carrier signal. To set the maximum
reference value of PI controller output is 0.6V. When the
carrier signal voltage is more than reference voltage that time
MOSFET go to OFF or 0 states. Otherwise the MOSFET
maintain the ON or 1 state.
Figure 7: Simulation results of separately excited DC motor
(a) Speed, (b) Armature Current, (c) Electrical Torque and
(d) Field Current
Figure 8: PWM Generation (a) PI and Triangular multicarrier
and (b) PWM Pulses
The simulation circuit is necessary to get the output
waveform. For the PWM generation, there are two signals
given to the relational operator one from PI controller output
signal and other from triangular carrier signal and the
relational operator output is PWM signal, that signal is given
to the switch. The Figure 8 shows the PI controller output and
triangular multi carrier signal. The Figure 9(a), (b), (c) and (d)
show the Speed, Armature Current, Electrical Torque, Filed
Current of the separately excited DC motor.
Figure 9: Simulation results of separately excited DC motor
(a) Speed, (b) Armature Current, (c) Electrical Torque and
(d) Field Current
VI. CONCLUSION
The speed of a DC motor has been successfully
controlled by using Chopper as a converter and
Proportional-Integral type controller as a speed and current
controller based on the closed loop model of DC motor.
Initially a simplified closed loop model for speed control of
DC motor is considered and requirement of current
controller is studied. Then a generalized modeling of DC
motor is done. After that a complete layout of DC drive
system is obtained. The MATLAB/SIMULINK model
shows good results under below the rated speed during
simulation. The simulation output creates the constant
armature voltage and constant field current that time speed
and torque of DC motor also produced constant output. Here
using buck converters the switching losses will be reduced
and motor efficiency are reach approximately more than
95%.
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Controller with PSO Algorithm"International Journal Of Engineering
And Computer Science (IJECS), https://www.ijecs.in, Volume 6 Issue
3, March 2017, 20477-20484, DOI: 10.18535/ijecs/v6i3.14
R. Nagarajan received his B.E. in Electrical
and Electronics Engineering from Madurai
Kamarajar University, Madurai, India, in 1997.
He received his M.E. in Power Electronics and
Drives from Anna University, Chennai, India,
in 2008. He received his Ph.D in Electrical
Engineering from Anna University, Chennai,
India, in 2014. He has worked in the industry as
an Electrical Engineer. He is currently working as Professor of
Electrical and Electronics Engineering at Gnanamani College of
Technology, Namakkal, Tamilnadu, India. His current research
interest includes Power Electronics, Power System, Soft
Computing Techniques and Renewable Energy Sources.
S.Sathishkumar received his B.E. in Electrical
and Electronics Engineering from Anna
University, Tiruchirappalli, India, in 2011. He
received his M.E. in Power Electronics and
Drives from Anna University, Chennai, India,
in 2014. He has worked in the industry as an
Electrical Engineer. He is currently working as
a Assistant Professor of Electrical and
Electronics Engineering at Gnanamani College of Technology,
Namakkal, Tamilnadu, India.
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