Reviews of Cascade Control of Dc Motor with Advance Controller

IJSRD - International Journal for Scientific Research & Development| Vol. 1, Issue 5, 2013 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 1121
Abstract-- The proportional- integral-derivative (PID)
control is the most used algorithm to regulate the armature
current and speed of cascade Control system in motor
drives. The controller uses two PID controllers. One PI
controller is for speed control and second PID controller for
current control in cascade structure. Inner loop is for the
current control which is faster than the outer loop. Outer
loop is for speed control. The output of the encoder is
compared with a preset reference speed. The output of the PI
controller is summed and is given as the input to the current
controller.
Keywords: DC motor, encoder, cascade control, speed
control, current control, PI controller and PID controller,
PIC18F microcontroller.
I. INTRODUCTION
Brushed DC Motors have been widely used in many
industrial applications such as electric vehicles, steel rolling
mills, electric cranes, and robotic manipulators due to
precise, wide, simple, and continuous control characteristics.
Small DC motors (in fractional power rating) are used in
control devices such as encoder for speed sensing and
servomotors for positioning. [4]
In this type of control there are two control loops, inner one
for controlling current and outer one for speed control. In
cascade control, two proportional-integral-derivative (PID)
controllers are used, which removes the delay and provides
fast control.
Fig. 1: Permanent magnet brushed dc motor
In this paper, section-1 is the fundamentals of the DC motor.
In section-2, cascade PID structure is explained. In section-
3, papers reviews are shown. In section-4, future scope is
explained and given the conclusion.
II. FUNDAMENTALS OF DC MOTOR
DC motor transfer function can be obtained by the following
equations
The armature circuit equation is:
(t)= +e (1)
Where
(t) is the armature voltage, e is the back EMF, is the
armature current, and are the armature resistance and
armature inductance respectively.[4]
The back EMF can be written as
e= (2)
Where
is a constant for the machine and w is the angular speed
of rotation.
The equation of mechanical part is:
(3)
Where J is the moment of inertia, b is the viscous friction
coefficient.
Developed torque is:
(4)
Taking Laplace transform of all forgoing equations assume
zero initial conditions for all variables, the DC motor
transfer function can be obtained as[4]
G ( ) ( )
(5)
So, DC motor is second order system. When there are no
parameters specifications of the system, system
identification is used to build mathematical modeling of the
dynamic system based on measured data. Overall system is
represented in block diagram form as shown in Figure-2, In
which voltage signal Va is applied to electrical system and
then by multiplying with K1-back emf, torque-T will go to
mechanical system. W is the output speed which is
measured by K2- speed sensor and then go back to the
reference signal.
-
Fig. 2: DC motor block diagram
III. CASCADE CONTROL STRUCTURE
In a cascade control system there is one or more control
loops inside the primary loop, and the controllers are in
cascade The (first) loop inside the primary loop is called the
secondary loop, and the controller in this loop is called the
secondary controller (or slave controller). The outer loop is
called the primary loop, and the controller in this loop is
called the primary controller (or master-controller). The
control signal calculated by the primary controller is the set
point of the secondary controller. The purpose of the
Reviews of Cascade Control of Dc Motor with Advance Controller
Bhavina Rathod1
1
PG Student, Applied Instrumentation
1
L. D. College of Engineering, Gujarat, India
T(s)
1
Electrical
system
K
1
Mechanical
system
𝑘 𝑡
𝑘
K2
W(s)
+
Va(s) Ia(s)

(IJSRD/Vol. 1/Issue 5/2013/021)
secondary loop is to compensate quickly for the disturbance
so that its response in the primary output variable of the
process is small. For this the secondary loop must have
register the disturbance. Cascade control can give
substantial compensation improvement. Cascade control can
also give improved tracking of a varying set point, but only
if the secondary loop has faster dynamics than the second
process.
IV. LITERATURE REVIEWS
Proportional-Integral-Derivative (PID) control is the best-
known controller in industries. PID offers simple structure
as well as robust performance for the dc motor system. PI
controller is always been compared to PID and PD
controller. PI controller is suited for dominant dead time
where constant>dead time and PID controller is suited for
dominant time constant and no noise from the transmitter.
Derivative, D is used when the loop has low noise and to
increase the stability. If the loop contains high noise, D will
increase the noise in high frequency and make the output
jittery. D is not suitable for pure dead time process. It will
cause the loop to become unstable.
From reference paper-3, it concludes that cascade PID is
better than single PID speed control. In paper-1&2, there is
used Anti-windup PID with limiter for current peak control
application and elimination of integral error in PI speed
control application. In paper-4 the PI current controller is
replaced by IMC-tuned PID controller to eliminate the
overshoot in current loop and then the overshoot in speed
loop.
In most applications improved compensation — not
improved tracking — is the main purpose of cascade
control.
Cascade PID is tuned as follow:
1. First the secondary controller is tuned, with the
primary controller in manual mode.
2. Then the primary controller is tuned, the secondary
controller in automatic mode.
There are so many methods available to find the PID
parameters. The P, I & D parameters can be found by using
relay feedback technique connected with system. By using
this we can calculate the ultimate time (Pu) and Ultimate
gain (Ku) from oscillations of output waveforms, then using
Z-N technique Kp, Ki, & Kd is found. Thus controller is
tuned for that system.[3] Finding the value of relay
amplitude (d) and output amplitude (a), we will get the
ultimate gain by computing these values in the following
equation
= (8)
V. FUTURE SCOPE
Cascade PID control will be used by making two loops,
inner for current control which is as secondary loop with
secondary PID type controller and outer one is for speed
control as the primary loop with master PID type controller
as shown in the figure-3. First current loop will be
controlled and find the PID parameters and then speed loop
will be controlled by making automatic current control loop.
Implementation of the cascade PID controller on the PIC18F
Fig. 3: Cascade control of the system
Microcontroller is as shown in figure-4. In that encoder
gives the PWM signals from the DC motor and send the
digital signals to microcontroller. Microcontroller gives the
low level digital signal (5V) which is converted by isolator
in high level digital signal (12V) sufficient for DC motor.
System implementation requires the basic equipments:
isolator, RS-232 USB driver, power supply.
Digital code low level code high level code
Figure 4: Implementation of the system
PID algorithm will be developed in PIC18F 2431
microcontroller.
PIC18F microcontroller has good features for dc motor
speed control. It includes:
1. 14-bit Power Control PWM Module
2. Motion Feedback Module
1.Three independent input capture channels:
2.Flexible operating modes for period and Pulse
3.Width measurement
4.Special Hall Sensor interface module
5.Special event trigger output to other modules
6.Quadrature Encoder Interface:
7.2 phase inputs and one index input from
encoder
8.High and low position tracking with direction
9.status and change of direction interrupt
10.Velocity measurement
3. High-Speed, 200 Ksps 10-bit A/D Converter
4. Flexible Oscillator Structure
5. Two Capture/Compare/PWM (CCP) modules
6. Enhanced USART module
7. Flash/data EEPROM.[10]
For interfacing, L298 chip as dc motor isolator is used. It is
a high voltage, high current dual full-bridge driver designed
to accept standard TTL logic levels and drive inductive
loads such as relays, solenoids, DC and stepping motors.
Two enable inputs are provided to enable or disable the
device independently of the input signals. [11]
SPEED
CONTR
OLLER
CURR
ENT
CONT
ROLL
ER
INN
ER
SYS
TEM
EXT
ERN
AL
SYS
TEM
Y u
u
1
y
2
y
INNER
LOOP
ENCODE
R
INTERFACING
CIRCUIT
DC
MOTOR
MICRO
CONTROLLE
R

(IJSRD/Vol. 1/Issue 5/2013/021)
VI. CONCLUSION
PID control method is accurate for output control with
disturbance rejection but it will give rise to produce high
starting current which can be dangerous for control circuitry
or motor for high capacity motor operation, while cascade
control method will give best set point tracking (Servo
response) and disturbance rejection (regulation) with
reduced starting current, which can be used for low as well
as high capacity motors. In cascade structure, for better
improvement tune the PID controller in good manner such
that it will give robust response in speed and current loop.
Implementation of PID control algorithm will make on
PIC18F microcontroller.
REFERENCES
[1] M.Nizam.Kamarudin and Sahazati Md.Rozali,
―Simulink Implementation of Digital Cascade control
DC motor model – A didactic Approach,2008‖ 2nd
International conference power and energy(PECon08)
December 1-3.
[2] Anirban Ghoshal and Vinod John, ―Anti-windup
Schemes for Proportional Integral and Proportional
Resonant Controller,2010‖ NATIONAL POWER
ELECTRONIC CONFERENCE.
[3] Lalit S. Patel, K.C.Dave. ―Cascade control Technique
for D.C.Motor Speed Control, 2011‖ International
Conference on Science and Engineering.
[4] Ibrahim K., Rateb Issa. ―Overshoot Elimination in
Cascade Control of Separately Excited DC Motors,
2012‖ European Journal of Scientific Research,
pp.98-104
[5] Mehmet AKAR, Mahmut HEKIM, Ismail TEMIZ,
Zafer DOGAN. ―The Speed and Torque Control of
Direct Current Servo Motors by using Cascade Fuzzy
PI Controller, 2012‖
[6] C. Agees Kumar, N. Kesavan Nair. ―Multi Objective
Cascade Control System Design for Speed Control of
Permanent Magnet DC Motor Drives,2012‖ European
Journal of Scientific Research
[7] Mohd Azri Bin Abd Mutalib. ―Speed control of DC
motor using PI Controller‖,2008.
[8] A.Purna Chandra Rao,Y. P. Obulesu, CH. Sai babu
―Robust internal model control strategy based pid
controller for bldcm,2010‖ International Journal of
Engineering Science and Technology.
[9] W.L. Soong. ―DC Machines : Parameter
Measurement
and Performance Prediction,2008‖ Power
Engineering Briefing Note Series.
[10] Microchip, PIC18F2331/2431/4331/4431Data Sheet.
[11] WWW.ALLDATASHEET.COM, L298, DUAL
FULL-BRIDGE DRIVER.
[12] USB MAX-232 datasheet.

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