International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 5 - Mar 2014
Design and Implementation of PI
Controller for the Speed Control of DC
Motor in Cooling System
Aruna.K1, Pravin.M.R2, Ramachandran.J3, Sudheer.S4, Sathiyasekar.K5
1, 2,3
UG Student, 4Senior Lecturer, 5Professor, EEE department, S.A.Engineering College
Chennai, TamilNadu, India
Abstract— In recent days power consumption is
becoming one of the most important constraints. This
paper presents the design and implementation of PI
controller using FPGA for the speed control of DC
motor in the cooling system. In many industrial
applications like Transformer, diesel engine etc., there
is need to maintain the temperature to prevent the
system from damage. Here the PMDC (Permanent
Magnet DC) motor is used to drive the cooling fan in
cooling system because they offer several advantages
like no field winding, small in size, increase in
efficiency .This study includes real time temperature
control using a PI controller implemented on FPGA.
The terminal voltage of the motor is controlled by
using chopper, here MOSFET is used as a switching
device in which the on and off time depends on the
temperature variation. PI controller and PWM
technique are used to control the speed which is
described. The temperature variation and speed of
the motor can be monitored in LCD display. The
power saving can be done by automation in the speed
control of the motor. The controller is modelled and
the concept is proven using Mat Lab and the final
simulation results are presented as well.
displacement between the stator current and back
electromotive force (EMF).
But PMDC motors have the advantages like
no field winding, small in size, increase in
efficiency. Since the motor's field, created by the
permanent magnet, is constant, the relationship
between torque and speed is very linear. A
Permanent Magnet DC motor can provide
relatively high torque at low speeds and
permanent magnet field provides some inherent
self-braking when power to the motor is shutoff.
Due to decoupled nature of field and armature
mmf’s DC motors exhibit outstanding drive
performance characteristics. By using variable
battery tapping’s, variable supply voltage,
resistors or electronic controls we can achieve
speed control [1]. This paper presents the speed
control by PWM technique along with the PI
controller and the block diagram of proposed
system is shown in Fig. 1.
II.BLOCK DIAGRAM
Index
termsField
Programmable
Gate
Arrays(FPGA), MOSFET, Proportional–Integral (PI)
controller, Pulse Width Modulation(PWM).
I.INTRODUCTION
Energy consumption is becoming one of the
major constraints in all Electric Motor Driven
Systems (EMDS).In recent few decades all
countries are challenged with high energy prices
pressure. Both more developed and less
developed countries are facing constant energy
consumption growth trends along with industrial
production rise. Motors are consuming over 40%
of all global electricity. In such circumstances,
main goal is to control energy consumption
increase of the above mentioned electric motors
and drives. Over 5 billion motors are built every
year worldwide and these motors are used in
many of the real time applications [3].
Likewise the cooling system also uses the
motors to exchange the heat. The fact is that the
most of them are single phase induction motors or
PMDC motors. Single phase induction motors are
characterized by low efficiency because of the
ohmic loss in the rotor and due to the phase angle
ISSN: 2231-5381
Figure 1 Block diagram of speed control of DC Motor in cooling
system using PI controller
A. Chopper
This N-Channel enhancement mode silicon gate
power field effect transistor is an advanced power
MOSFET designed, tested, and guaranteed to
withstand a specified level of energy in the
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 5 - Mar 2014
breakdown avalanche mode of operation. All of
these power MOSFETs are designed for
applications such as switching regulators, switching
converters,
motor drivers, relay drivers, and drivers for high
power bipolar switching transistors requiring high
speed and low gate drive power. These types can be
operated directly from integrated circuits. So
MOSFET is used as chopper device.
Vemf = back emf voltage (V)
J = Inertial load (kgm2/s2)
C.FPGA-Field Programmable Gate Array
B.PMDC Motor
Permanent Magnet DC brushed motors (PMDC
motors) consist of permanent magnets, located in
the stator, and windings, located in the rotor. The
ends of the winding coils are connected to
commutator segments that make slipping contact
with the stationary brushes. Brushes are connected
to DC voltage supply across motor terminals.
Change of direction of rotation can be achieved by
reversal of voltage polarity. The current flow
through the coils creates magnetic poles in the rotor
that interact with the permanent magnet poles. In
order to keep the torque generation in same
direction, the current flow must be reversed when
the rotor north pole passes the stator south pole.
The equivalent circuit of dc motor is shown in
Fig 2.The torque, T is related to the armature
current, i by a constant factor KtT = KtIa . For the
separately excited DC motor, the back emf, e is
related to the rotational velocity by:
e = Kb uT..................................................... (1)
Figure 2 Equivalent representation of DC motor
In SI units Kt (armature constant) is equal to Kb
(motor constant).
V = input voltage (V)
R = nominal resistance (Ω)
L = nominal inductance (H)
Ia = armature current (A)
ISSN: 2231-5381
Figure 3 FPGA-Field Programmable Gate Array
The Spartan-3E family of Field-Programmable
Gate Arrays (FPGAs) is VLSI based hardware as
shown in Fig.3 which is specifically designed to
meet the needs of high volume, cost-sensitive
consumer electronic applications. The five-member
family offers densities ranging from 1 lakh to 1.6
million system gates. The Spartan-3E family builds
on the success of the earlier Spartan-3 family by
increasing the amount of logic per I/O, significantly
reducing the cost per logic cell. New features
improve system performance and reduce the cost of
configuration.
These
Spartan-3E
FPGA
enhancements, combined with advanced 90 nm
process technology, deliver more functionality and
bandwidth per dollar than was previously possible,
setting new standards in the programmable logic
industry. Because of their exceptionally low cost,
Spartan-3E FPGAs are ideally suited to a wide
range of consumer electronics applications,
including broadband access, home networking,
display/projection,
and
digital
television
equipment.
The Spartan-3E family is a superior alternative to
mask programmed ASICs. FPGAs avoid the high
initial cost, the lengthy development cycles, and the
inherent inflexibility of conventional ASICs [2][7].
Also, FPGA programmability permits design
upgrades in the field with no hardware replacement
necessary, an impossibility with ASICs.
D.Sensors
i) Temperature sensor
The AD590 is a two-terminal integrated
circuit temperature Transducer that produces an
output current proportional to absolute temperature.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 5 - Mar 2014
For supply voltages between +4 V and +30 V the
device acts as a high impedance, constant current
regulator passing 1 mA/K ,which has the wide
temperature range -55 to 150 ºc The inherent low
cost of a monolithic integrated circuit combined
with the elimination of support circuitry makes the
AD590 an attractive alternative for many
temperature measurement situations.
power consumption. Pulse Width Modulation
(PWM) is a dominant technique for controlling
analog circuits with digital signals [4][5][9].PWM
is a way of digitally encoding analog signal levels.
The duty cycle of a square wave is modulated to
encode a specific analog signal level, as shown in
this Fig. 4.
ii) Speed sensor
MOC7811 sensor is used to count the number of
rotations of the aluminium disc which is coupled
with shaft of the motor.MOC7811 is a slotted Opto
isolator module, with an IR transmitter & a
photodiode mounted on it. This is normally used as
positional sensor switch (limit switch). Actually it
has four legs. 2 legs for diode and 2 for transistor.
Both are inbuilt, no external connection required.
Of course, current limiting resistance is required.
E. PI motor control
Speed control of an Industrial motor is very
complicated.
This
thesis
presents
the
implementation of a Digital PI (Proportional,
Integral) controller on FPGA. A controller is a
device in the system to sense the error signal and to
produce the required control signal. An automatic
controller compares the real value of the output
with the desired value, determines the deviation,
and produces a control signal which will reduce the
deviation to zero or to a minimum value [8].
Controllers are classified as proportional (P),
integral (I), derivative (D) and their combinations
(PI, PD and PID)[6].
Figure 4 PWM Duty Cycle
The PWM signal is digital still because, at any
instant, it is either on or off. The relation between
the on time and the off time varies according to the
analog level to be represented. Given a sufficient
bandwidth, any analog value may be encoded with
PWM.
A proportional controller amplifies the error
signal by a quantity Kp, which produces a control
signal u(t), which is proportional to the input error
signal, e(t).
u(t) = Kp * e(t) .....................................................(2)
Where Kp = proportional gain or constant;
Integral control reduces the steady state error to
zero. This device produces a control signal u(t) that
is proportional to the integral of the input error
signal.
u(t) = Ki * integral {e(t)*dt}................................(3)
where Ki = integral gain or constant
F. Digital control with PWM
The PI Controller is functioning based on the
technique known as Pulse Width Modulation
(PWM). This technique allows an analog interface
that can be built without A/D or D/A converters,
and analog voltages and currents can be used to
control processes directly. Controlling analog
circuits digitally will reduce system costs and
ISSN: 2231-5381
Figure 5 PWM Signal Generation
PWM is used to generate the gating signals for
the chopper circuit. The speed of a DC motor can
be controlled by varying its input voltage.
G. RPM calculation and speed display
MOC7811 Sensor is used to sense the speed and
given it in the form of pulse. That is given to ADC
and the corresponding digital value is transmitted
and displayed in the appropriate display (LCD).
General RPM calculation is based on the signals
period count set in the counter due to the interrupt
produced by the timer.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 5 - Mar 2014
III.FUNCTIONAL BLOCK DIAGRAM
IV.SIMULATION RESULT
The Fig. 6 represents the functional block diagram
The Fig.7 shows the block diagram of
MATLAB Simulation modelling of the proposed
system.The upper parts are the switching device,
motor. The lower parts are PWM generator and PI
Controller.
Figure 6 Functional block diagram
TABLE I. Variation of Speed with respect to the
temperature
TEMPERATURE RANGE
RPM
Above 60°C
1500
40°-60°C
1200
30°-40°C
1000
Below 30°C
0
Figure 7 MATLAB Modelling
Fig. 8 shows the waveform of speed of DC
motor with respect to time and Fig. 9 shows the
waveform of switching time of MOSFET at 1500
rpm. Simulation results prove the effectiveness of
the proposed system.
The Table 1 shows the variation of speed of the
motor with respect to the temperature .When the
temperature of the system is high, consider above
60°C the motor will rotate at maximum speed of
1500 rpm for effective cooling. Similarly when the
temperature decreases and the speed of the motor
also decreases correspondingly. When the condition
of temperature reaches below30°C the motor is set
to shut down, which means that 0 rpm and the
power saving can be done successfully.
In this process the speed of the motor depends on
the terminal voltage which can be controlled using
chopper. All the above operations are performed
based on the PWM technique and PI control. In the
PI control, the reference value is taken from
temperature sensor output and the actual value is
taken from the speed sensor output. Moreover the
PI control has been one of the best control system
design methods which is extensively used now
because of its advantages like robustness, smooth
tuning, minimised transient response. The PI
control output is fed to PWM and the
corresponding pulses are given to chopper for the
speed control of the motor.
ISSN: 2231-5381
Figure 8 PI controller response (Time Vs Speed)
The response of Proportional Integral (PI)
controller is shown in Fig. 8 for a set value speed of
1500 rpm with PI control. It is inferred that the
actual set value of 1500 rpm is achieved with
settling time of 0.4 sec before reaching the set
point.
The terminal voltage of the motor can be
controlled by modulating the duty cycle and the
terminal voltage ( VDC) is calculated as,
VDC = V
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 5 - Mar 2014
[7]
[8]
[9]
Da Zhang, Hui Li and Emmanuel G. Collins“Digital
Anti-Windup PI Controllers for Variable-Speed Motor
Drives Using FPGA and Stochastic Theory”,
Proceedings of IEEE transactions on power electronics,
vol. 21, no. 5, september 2006.
Amit Vilas Sant , Nimit K.Sheth and Rajagopal. K.R
“Permanent Magnet Synchronous Motor Drive Using
Hybrid PI Speed Controller With Inherent and
Noninherent Switching Functions”, Proceedings of
IEEE transactions on magnetics, vol. 47, no. 10,
october 2011.
Chee Shen Lim, Emil Levi, Nasrudin Abd. Rahim and
Wooi Ping Hew “A Comparative Study of Synchronous
Current Control Schemes Based on FCS-MPC and PIPWM
for
a
Two-Motor
Three-Phase
Drive”,Proceedings of IEEE.
Figure 9 Waveform of switching time of MOSFET
V. CONCLUSION
In this work the speed control of DC motor based
on FPGA has been completed. The advantages,
simplicity of FPGA and reprogrammable capability
of the device can be used to design such a system
to control the motor speed. The PWM generation,
PI control strategy are realized and integrated in a
single FPGA which makes the system with very
flexibility and good real time control ability. So
controller designed using this system can be used to
gain high performance control of motor with fast
execution. The experiments are successfully
validated, and the experimental results show a good
performance.
VI. REFERENCES
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[6]
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