 Open Access
 Total Downloads : 3612
 Authors : Pragnesh Patel, A. S. Sindekar
 Paper ID : IJERTV1IS5315
 Volume & Issue : Volume 01, Issue 05 (July 2012)
 Published (First Online): 03082012
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Modeling and Analysis of Slip Power Recovery Controlled Induction Motor Drive
Pragnesh Patel
PG Scholar Electrical Engg. Department Govt. College of Engg. Amravati Amravati, India
A. S. Sindekar
Head of Electrical Engg. Department Govt. College of Engg. Amravati Amravati, India
Abstract A control system based on PI_PI controller is used to improve the dynamic performance of slip power recovery motors, in which one PI controller is used as auto speed regulator (ASR) and second is used as auto current regulator (ACR). This controller tracks the need of speed and limit the stator current. The parameter values of PI controller are adjusted relaying on mathematical model value such as electromagnetic time constant and magnification factor. The simulation results of this control strategy for motor drive show that this system has high antidisturbance capacity, fast response, low overshoot, so the system dynamic performance is improved.
KeywordsPI_PI controller; motor drive speed control; modeling and simulation.

INTRODUCTION
The technology of slip power recovery controlled by chopper for slip ring induction motor has been widely applied in highvoltage largecapacity motor because of higher power factor, higher efficiency and lower control voltage than those without chopper. In this, both inner current loop and outer speed loop are designed with conventional proportionalintegralderivative (PID) controller to control the motor drive automatically.
Figure1. Control scheme of slip power recovery with chopper for motor drive
In this paper, a doubleclosedloop control system based on PI_PI controller is presented to improve the dynamic performance of slip power recovery drives. This
motor drive control system is shown in Figure 1, in which, one PI controller is used as auto speed regulator and second is used as auto current regulator.
We will further illustrate the designs steps and the effectiveness of this control scheme via simulation experiments in MATLAB/SIMULINK.

PROPOSED CONTROL SCHEME
This new type of double closed loop control system shown in Fig. 1 is proposed for the speed control of the nonlinear, time varying and complex motor system, in which one PI controller is used as auto speed regulator and second is used as auto current regulator.
A. Principle of speed regulation
From the slip power recovery circuit shown in Fig. 1, the threephase fullwave diode bridge rectifier connects to the rotor windings via slip rings, converters a portion of slip power into DC which in turn converted into line frequency AC by a threephasethyristor inverter and fed back to the AC mains. The inductor L1, L2 between rectifier and inverter are placed to reduce the DC current ripple. The diode between L1 and L2 is used to keep current when IGBT is off and isolate when IGBT is on. The capacitor C is used to store the energy in the loop by keeping voltage Uc at low ripples.
By using IGBT as chopper, the inverter is always fixed at the smallest inverter angle of about /6rad and the equivalent additional reverse electromotive force is obtained by changing the duty cycle of IGBT chopper. As a result, the electromagnetic torque and motor speed is changed. So the purpose of changing the motor speed can be achieved by adjusting the duty ratio of IGBT chopper.
Neglecting higher order harmonics and power losses in rectifier and converter, equivalent circuit combined with converter, DC link, IGBT chopper and inverter is shown in figure 2.
Where
d duty ratio of IGBT
T
Ts = sum of IGBT trigger pulse cycle and threephase bridge rectifier out of control time
Figure2. DC Equivalent Circuit
Where, UD is the rotor rectifier voltage, UB is the active
S n0 n n0
slip of induction motor drive
inverter DC voltage, Rd is the equivalent resistance of rotor rectifier circuit, Ld is equivalent inductance for the rotor rectifier, Rb is equivalent resistance of the inverter circuit, Lb is equivalent inductor for the inverter circuit.
R 2( Rs
d k 2
3X
Rr )
3X D S
A. Mathematical model
Mathematical model is the foundation of system analysis and correction. In engineering applications, the range of variation of capacitance voltage Uc is small. Let us assume that Uc is constant and the disturbance of Uc
L 2 D L
d 100 1
The mechanical motion equation of motor drive system is given as:
is approximately equal to 0. Using the average model method, the average value equivalent circuit is obtained as shown in Fig. 3.
Te TL
GD 2 dn
375 dt
(2.4)
Where
Electromagnetic torque Te
CM I d
2.34E20
3X D
I
d
Figure3. (a) The average value equivalent circuit and (b) waveform of back voltage
Then
Torque coefficient CM 2 f
p
In figure 3, considering the power switching device IGBT has lag aspect, the transfer functions of this circuit is given as follows:
n s
I d s I L
(s)
375CM 1
GD 2 s
1
Tm s
(2.5)
U (1 d )U c
From the abovementioned formula, the block diagram of openloop system is developed as shown in figure 4.
i
(2.1)
Ts s 1
U D 2.34E20 S
I d 1 Rd
K Lr
(2.2)
(2.3)
U D U I
Ld s 1
Rd
TLr 1
Figure4. Block diagram of openloop motor drive system

DOUBLE CLOSED LOOP CONTROL SYSTEM
DESIGN

Design of ACR_PI in inner current loop
In double closed loop design procedure, the first step is to design the controller for inner current loop and to tune the parameters. The current response is fast because the time constant of inner loop is small. According to a typical design method explain in [5], PI controller for auto current regulator (ACR) used for meeting the demand of servo performance is designed as follows.
The form of PI controller can be written as

Design of ASR_PI in outer speed loop
In double closed loop design procedure, the second step is to design the control1er for outer speed loop and to tune the parameters. This controller is designed by using ZieglerNichols rules for tuning PID controller. Ziegler and Nichols proposed rules for determining value of the proportional gain Kp, integral time Ti, and derivative time Td based on transient response characteristic of a given plant.
There are two methods called ZieglerNichols tuning rules, in second method we first set Ti = and Td
= 0. The proportional control action only increases Kp from 0 to a critical value Kcr at which the output exhibit sustained oscillations. Thus, the critical gain Kcr and the corresponding period Pcr are determined. Ziegler and Nichols suggested to set the values of the parameter Kp, Ti, and Td according to table 1.
Type of controller
Kp
Ti
Td
P
0.5Kcr
0
PI
0.45Kcr
1 Pcr
1.2
0
PID
0.6Kcr
0.5Pcr
0.125Pcr
TABLE.1 ZIEGLERNICHOLS TUNING RULE BASED ON CRITICAL GAIN KCR AND CRITICAL PERIOD PCR(SECOND METHOD)
WACR
(s)
Kic (
ic s 1)
ic s
Kic 1
1
ic s
(3.1)
The PID controller tuned by the second method of ZieglerNichols rules gives
The parameters of ACRcan be chosen as follow
Gc s
K p 1
1
Ti s
Td s
T K ic
ic
0.6Kcr 1
1
0.5P s
Pcr s
ic Lr
2Ts
*U C
* K Lr cr
2
s 4
Then the transfer function of innerclosedIoop WCL_i(s) will be similar to a typical secondorder system, which is given as:

K cr Pcr
Pcr
s
(3.3)
2
s
1 2T
Now, by using this method the ASR_PI controller
for outer speed loop is designed.
WCL _ i s
S 2 2 2 1
2
2Ts S 1
2
2Ts
The form of PI controller can be written as
1 WASR (s)
Kis (
is s 1)
1
Kis 1
2
2
2Ts S
2Ts S 1
(3.2)
is s
is s
(3.4)


SIMULATION AND EXPERIMENTAL RESULTS The simulation tests have done by using PI_PI
controller in double closed loop for motor drive speed regulation system.
Using MATLAB/SIMULINK, the simulation model of motor drive speed control is built. Figure5 shows the model of speed control system using PI_PI controller.
150
Motor Speed n (rad/sec)
100
50
0
0 1 2 3 4 5 6 7 8 9 10
Time(second)
Figure5. Simulation model
A slip ring induction motor of 500 kW, 2.3 kV and 50 Hz frequency is used for experiment. Parameters of this motor are given below.
Pole pair = 2
Stator resistance Rs = 1.115 Rotor resistance Rr = 1.085
Inductance of stator winding Ls = 0.005974 H Inductance of rotor winding Lr = 0.005974 H Magnetizing reactance Lm = 0.2037 H
That response curve of the motor speed is shown in Figure6, which shows that response having peak overshoot of 21.97 rpm and settling time of 1 second. Figure7 shows the speed curve of induction motor in which rotor speed is changed from 144 rad/sec to 100rad/sec.
150
Motor Speed n (rad/sec)
100
50
0
0 1 2 3 4 5 6 7 8 9 10
Time(second)
Figure6. Speed curve of dynamic response
Figure7. Speed curve of dynamic response when speed change from 144 rad/sec to 100 rad/sec.
V. CONCLUSION
In this paper, simulation of a double closed loop slip power recovery in induction motor, with chopper is obtained by using PI controller as both speed regulator and current regulator. The PI controller for double closedloop is designed and the simulations are performed. The simulation results show that the PI_PI doubleloop speed control system reduced the peak overshoot and obtained the rapid and smooth response against the modeling uncertainty and disturbance. So, it is an effective method to improve the robust and adaptability performance for induction motor.
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Ping Jiang, Bingshu Wang and Junwei Zhang, Simulation of a new method in double closed loop for slip power recovery motor with chopper Proc. in IEEE international conference on mechatronics and automation, Aug 912, Changchun, China, 2009.

P. C. Sen, Power electronics, Tata McGraw Hill Publishing Company, New Delhi, 2007.

Jai P. Agrawal, Power Electronic Systems Theory and Design, Pearson Education Asia, Delhi,2004

Zeguo Wei, The principle and Application of casecade speed control system with SCR, Metallurgical Industry Press, Beijing, 1985.

Katsuhiko Ogata, Morden control Engineering, Fifth Edition, PHI Learning Private Limited, New Delhi, 2010.