Modeling and Analysis of Slip Power Recovery Controlled Induction Motor Drive

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 anti-disturbance capacity, fast response, low overshoot, so the system dynamic performance is improved.

Keywords-PI_PI controller; motor drive speed control; modeling and simulation.

1. INTRODUCTION

   The technology of slip power recovery controlled by chopper for slip ring induction motor has been widely applied in high-voltage large-capacity 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 proportional-integral-derivative (PID) controller to control the motor drive automatically.

   Figure1. Control scheme of slip power recovery with chopper for motor drive

   In this paper, a double-closed-loop 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.

2. 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 three-phase full-wave 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 three-phase-thyristor 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 three-phase 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 above-mentioned formula, the block diagram of open-loop 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 open-loop motor drive system

3. DOUBLE CLOSED LOOP CONTROL SYSTEM

   DESIGN

   1. 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

   2. 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 Ziegler-Nichols 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 Ziegler-Nichols 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 ZIEGLER-NICHOLS 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 Ziegler-Nichols 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 inner-closed-Ioop WCL_i(s) will be similar to a typical second-order system, which is given as:

   1. 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)

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 closed-loop is designed and the simulations are performed. The simulation results show that the PI_PI double-loop 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.

REFERENCES

1. E. O. Taylor, The performance and design of ac commutator motors, Wheeler publishing & Co Ltd, New Delhi, 2004.

2. 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 9-12, Changchun, China, 2009.

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

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

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

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