Simulation of direct torque and flux control strategy for an induction motor

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  • 1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME & TECHNOLOGY (IJEET)ISSN 0976 – 6545(Print)ISSN 0976 – 6553(Online)Volume 4, Issue 1, January- February (2013), pp. 145-152 IJEET© IAEME: www.iaeme.com/ijeet.aspJournal Impact Factor (2012): 3.2031 (Calculated by GISI) ©IAEMEwww.jifactor.com SIMULATION OF DIRECT TORQUE AND FLUX CONTROL STRATEGY FOR AN INDUCTION MOTOR USING MATLAB/SIMULINK SOFTWARE PACKAGE Deepak Kumar Goyal M.Tech from IIT Roorkee Assistant Professor, Department of Electrical Engineering, Govt Engg. College, Bharatpur, Rajasthan., India ABSTRACT This paper describes a control scheme for direct torque and flux control of in induction motor based on stator flux estimation, which has many of the desirable features of conventional constant v/f ratio. The use of simple equation to obtain the control algorithm makes it easier to understand and implement. Switching instant and low torque ripple are obtained using voltage space vector. Keywords : control strategy, direct torque and Flux control, induction motor, space vector. I. INTRODUCTION In recent year many studies have been developed to find out different solution for induction motor control having the feature of precise and quick torque response, Flux control and reduction of the complexity of field oriented algorithms. The Direct Torque and Flux Control (DTFC) technique has been recognized as viable solution to achieve these requirements. In principle the DTFC selects one of the six voltage vector and two zero voltage vectors generated by a VSI in order to keep stator flux and torque within limits of two hysteresis bands. The right application of this principle allows a decoupled control of flux and torque without need of speed or position sensor, coordinate transformation, PWM pulse generation and current regulator. However, the presence of hysteresis leads to a variable switching frequency operation. In [3]-[4] different method has been presented which allow constant switching frequency operation. In general, they require control schemes which are more complex with respect to the basic DTFC scheme. 145
  • 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEMEII. INDUCTION MOTOR MODEL The d-q axis dynamics equation for squirrel case induction motor with the referenceframe which rotating with ω speed are given by[7]vqs = Rs iqs + ωλ ds + pλqs − − − (1)vds = Rsids − ωλ qs + pλds − − − (2)vqr = Rr iqr + (ω −ω r )λ dr + pλqr − − − (3)vdr = Rr idr − (ω −ω r )λ qr + pλdr − − − (4)λqs = Lls iqs + Lm (i qs +iqr ) − − − (5)λds = Lls ids + Lm (i ds +idr ) − − − (6)λqr = Llr iqr + Lm (i ds +idr ) − − − (7)λdr = Llr idr + Lm (i ds +idr ) − − − (8) Because machine parameter is taken in per unit so it is convenient to express thevoltage and flux linkage in terms of reactance rather than induction. And now flux linkagebecome flux linkage per second.  ωb  ψ qs =   vqs −  ω ψ ds +  Rs ( mq −ψ qs ) − − − (9)     p  ω   X ψ      b  ls    ωb      ψ ds =   v ds −  ω ψ qs +  R s (ψ md − ψ ds ) − − − (10)  p   ω  X      b  ls    ωb  ψ qr =   vqr −  ω − ω r    R  ψ dr +  s ( mq − ψ qr ) − − − (11)  p     X ψ     ωb   lr    ωb  ψ dr =   v dr −  ω − ω r    R ψ qr +  s  (ψ md − ψ dr ) − − − (12 )  p   ω  X      b   lr   146
  • 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEMEand electromagnetic torque is given as  3  P  1  ( ds i qs − ψ qs i ds ) − − − (13) Te =      ψ  2  2  ω b   ψ ψ ψ mq = X aq  qs + qr  − − − (14) X   ls X lr  −1 ψ ψ   1 1 1 ψ md = X aq  ds + dr  − − − (15) Where X aq = X + X + X   X   ls X lr   ls lr m  1i qs = (ψ qs −ψ mq ) − −(16) X ls 1 i ds = (ψ ds −ψ md ) − − − (17 ) X ls 1 iqr = (ψ qr −ψ mq ) − − − (18) X lr 1i dr = (ψ dr −ψ md ) − − − (19) X lr As we require machine model in stator reference frame so put ω=0 and for squirrelcage induction motor vqr = 0 and vdr = 0 Rs and Rr are the stator and rotor resistance. Ls,Lr and Lm are the self and mutual induction. ωr is the rotor angular speed in electrical radian.III. THEORY OF DTFC[5]From eq. (1-2)λqs = ∫ (vqs − iqs Rs )dt − − − (20)λds = ∫ (vds − ids Rs )dt − − − (21)The stator flux is given by λs = (λ2 + λ2 )∠θ e − − − (22) qs ds 147
  • 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEMEThese v qs and v ds can be estimated as belowvqs = vas − − − (23)  1 vds =   (vcs − vbs ) − − − (24)  3And electromagnetic torque can be calculated as  3P Te =   (λds iqs − λqs ids ) − − − (25)  4 Fig 1 shows the block diagram of DTFC of an induction motor. As shown in Fig. 1, theinverter switching states are selected according to the error of the torque and flux, which areindicated by, ∆Te and ∆λs , respectively.∆Te = Te* − Te − − − (26)∆λs = λs* − λs − − − (27) + Vdc - ∆Te 1 HTe I Sa Te* + 0 VI II - -1 Sb VSI V Te III Sc IV ∆λs 1 Hλs * λ s - -1 λs Ia,Ib Torque and flux estimation Va,Vb Induction motor Fig. 1:Block diagram of DTFC of Induction motor induction motor Where Te* and λs* are reference torque and stator flux.The table II shows theassociated inverter switching states which are determined by the error of torque and flux, andposition of stator flux, which calculated as  λqs  θ e = tan −1   − − − (28)  λds  148
  • 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME θe S(k) (sector) п/3 <θe≤ 2п/3 S(1) 0 <θe ≤ п/3 S(2) -п/3 <θe ≤ 0 S(3) -2п/3 <θe ≤ -п/3 S(4) -п <θe ≤ -2п/3 S(5) 2п/3 < θe ≤ п S(6) Table I: Position (Sector ) of flux HTe Hλs S (1) S (2) S (3) S (4) S (5) S (6) 1 1 VI I II III IV V (1,1,0) (1,0,0) (1,0,1) (0,0,1) (0,1,1) (0,1,0) 1 0 VIII VII VIII VII VIII VII (1,1,1) (0,0,0) (1,1,1) (0,0,0) (1,1,1) (0,0,0) 1 -1 II III IV V VI I (1,0,1) (0,0,1) (0,1,1) (0,1,0) (1,1,0) (1,0,0) 0 1 V VI I II III IV (0,1,0) (1,1,0) (1,0,0) (1,0,1) (0,0,1) (0,1,1) 0 0 VII VIII VII VIII VII VIII (0,0,0) (1,1,1) (0,0,0) (1,1,1) (0,0,0) (1,1,1) 0 -1 III IV V VI I II (0,0,1) (0,1,1) (0,1,0) (1,1,0) (1,0,0) (1,0,1) Table II: Switching states for possible HTe, Hλs and S(k) Noting that an adjustable speed drives can obtain by adding a speed controller to generatetorque command. The phase voltage can be determined as V  vas =  dc  (2 S a − Sb − S c )  3  V  vbs =  dc  (2 Sb − S c − S a ) − − − (29)  3  V  vcs =  dc  (2 S c − S a − Sb )  3 Where vas , vbs , vcs are phase voltagesSa , Sb , Sc denote as inverter switching state, in which Si =1 (i=a,b,c), if the upper leg switch ison andSi =0 (i=a,b,c) if the upper leg switch is off.Vdc is the dc link voltage. 149
  • 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME q-axis VI VVI VII S(1) S(6) S(1) π/3 π/3 d-axis Reference S(5) π/3 S(3) S(4) VV VIII VIV Fig 2: Voltage Space Vector and Flux SectorIV. ADVANTAGE OF DTFC BASED DRIVES The field oriented control approach invokes the concept of transforming the stationaryquantities into synchronous ones and orienting the referred flux along the d-axis of thesynchronous frame while in contrast the DTFC does not invoke any such works.V. IMPLEMENTATION RESULT The figures (3 to 7) present simulation results based on model of a 10h.p. inductionmotor. Its main parameters are shown below. Rated power: 10 hp; rated voltage: 220V(line toline); rated frequency: 60 Hz; stator resistance Rs=.0453 p.u.; rotor resistance Rr =.0222 p.u.stator reactance Xls =.0775 p.u. rotor reactance Xlr = .0322 p.u.; mutual reactance Xm = 2.042p.u. and inertia H= .5 sec.VI. CONCLUSION In this paper, a direct torque and flux control scheme is presented. It based on theinduction motor model and space vector theory. As a result, both flux and torque can becontrolled separately without any transforming the stationary quantities into synchronousone. 150
  • 7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEMEVII. SIMULATION RESULTS 151
  • 8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEMEVIII. REFERENCES[1] Y.A.Chapuis, D.Roya, J.Davoine, “Principles and implementation of Direct Torque Control by stator flux orientation of an Induction Motor”, IEEE Applied Power Electronic conference and Exposition-Industry –Dallas, March 1995.[2] T.G.Habetler, “ Control Strategy for Direct Torque Control of Using Discrete pulse space Modulation”, IEEE Trans. Ind. App. , vol. 27, no. 5, pp.893-901, sept./oct. 1991[3] Yen-Shin Lai and Jian-Ho Chen, “ A New Approach to Direct torque control of induction motor for constant Inverter Switching Frequency and Torque Ripple Reduction”, IEEE Transaction on energy conversion, vol. 16, NO. 3, Sept. 2001[4] T.G.Habetler, “ Direct Torque Control of Using space Vector Modulation”, IEEE Trans. Ind. App. , vol. 28, no. 5, pp.1045-1053, sept./oct. 1992[5] R. Krishnan, “ Electric motor drives, modeling, analysis and control”, Prentice- Hall of india private limited, New Delhi-110001,2003[6] B.K. Bose, ”Modern Power electronics and AC Drives”, Published by Pearson Education (Singapore) pte, Ltd. Indian Branch, 2003[7] P. C. Krause, “Analysis of electric machinery”, McGraw-Hill, 2001.[8] P. Tiitinen, “The next generation motor control method, DTC direct torque control,” in Proceedingss of the IEEE Intl. Conf. on Power Electronics,Drives, and Energy Systems for Industrial Growth, 1996, pp.[9] Domenico Casadei, Giovanni Serra and Angelo Tani, “Improvement of Direct Torque Control Performance by using a Discrete SVM technique”, IEEE Trans. Ind. App. ,1998.[10] Vaibhav B. Magdum, Ravindra M. Malkar and Darshan N. Karnawat, “Study & Simulation of Direct Torque Control Method For Three Phase Induction Motor Drives” International Journal of Electrical Engineering & Technology (IJEET), Volume 2, Issue 1, 2011, pp. 1 - 13, Published by IAEME.[11] N. S. Wani and W. Z. Gandhare, “Voltage Recovery of Induction Generator Using Indirect Torque Control Method” International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 3, 2012, pp. 146 - 155, Published by IAEME.[12] Vishal Rathore and Dr. Manisha Dubey, “Speed Control of Asynchronous Motor Using Space Vector PWM Technique” International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 3, 2012, pp. 222 - 233, Published by IAEME.[13] Bhagirath Ahirwal and Prof. Tarun Kumar Chatterjee, “Effect of starting torque on the temperature rise and time tE of Increased Safety HT Induction Motor for Explosive Atmospheres” International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 2, 2012, pp. 223 - 235, Published by IAEME. 152