DIRECT TORQUE CONTROL OF THREE PHASE INDUCTION MOTOR USING FUZZY LOGIC SPEED CONTROLLER FOR STEADY/DYNAMIC STATE RESPONSE

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1 DIRECT TORQUE CONTROL OF THREE PHASE INDUCTION MOTOR USING FUZZY LOGIC SPEED CONTROLLER FOR STEADY/DYNAMIC STATE RESPONSE 1 C. MOHAN RAJ, 2 K.KEERTHIVASAN, 3 RANJITH KUMAR DINAKARAN, 4 N.PUSHPALATHA 1 (M.E), 2 M.E. (Ph.D), Karpagam Univerity, Coimbatore 3,4 Aitant Profeor, Sri Ehwar College of Engg, CBE c.mohanrajme@gmail.com, kdv1999@gmail.com, drk.ranjithkumar@gmail.com, puhpa_latha_88@yahoo.co.in Abtract- Thi paper preent a Space Vector-PWM baed DTC control of the three-phae Induction Motor uing a fuzzy logic controller (FLC) for good peed regulation and lower electromagnetic torque ripple. Induction Motor ha a three phae winding with the operating frequency of 50/60Hz and the operating voltage of 230VAC. DTC i achieved by comparing the motor actual torque and operating flux with the motor reference electromagnetic torque and flux value directly. Conventional DTC method ue the tatic PI controller in a peed regulation loop to generate the flux reference and torque reference value. The main drawback of the conventional DTC i high tator flux and electromagnetic torque ripple and the peed of Induction motor i reducing under tranient and dynamic tate of operating condition. Thee drawback were reduced in propoed DTC method. In propoed method, the tatic PI controller i replaced by the Fuzzy Logic Controller. Fuzzy logic peed controller generate the torque reference value and flux reference value baed on the peed error. Simulation reult how that the propoed DTC method give the better performance in the Induction Motor than conventional DTC method. Index Term- FLC- baed DTC, IGBT baed inverter, PI-Speed controller, Low torque ripple, dynamic repone I. INTRODUCTION The ytem employed for motion control i known a an electric drive. In general, electric drive are ued to control the motor peed and torque in both teady tate and dynamic tate operation. Now a day 75% of the utility power i conumed by the electric drive. Electric motor convert the electrical energy to mechanical energy. Mechanical energy i upplied to the load through the mechanical haft. There are two phyical quantitie decribe the tate of the mechanical haft: torque and peed. To control the mechanical power flow to the load, we mut control the any one of the two quantitie and we peak of peed control and torque control. In torque control mode, the motor peed i decided by the load. Likewie in Speed control mode, torque i decided by the load. There are two type of electric drive namely AC drive and DC drive. In early day DC drive were employed for peed control and torque control. Independent control of field and armature i poible in DC motor. Flux produced by the field winding i alway right angle to flux produced by the armature winding. Thi condition i called field orientation. In dc motor, field orientation i achieved by the mechanical commutator and bruh aembly poition. So the maximum torque i achieved irrepective of the rotor poition. Speed control and torque control i obtained by independent control of field and armature flux. The main drawback of DC drive i the reduced reliability of the DC motor; the fact that bruhe and commutator wear down and need regular ervicing; that DC motor can be cotly to purchae; and that they require encoder for peed and poition feedback.ac drive technology 2 nd International Conference On Emerging Trend in Engineering & Techno-Science (ETETS)-13 th Apr 2014 ISBN: eliminate thee drawback becaue of it rugged contruction, maintenance free due to abence of bruh and commutator aembly and Low cot. The DC motor performance can alo be obtained in AC Induction motor by implementing uitable AC drive control trategy. AC drive are mainly employed for controlling the Induction Motor peed and torque. Induction motor peed control i achieved by the two control method namely calar control and vector control hown in Fig.1. In calar control the operating quantity magnitude i alone controlled. But in vector control method, the operating quantity both magnitude and phae angle are controlled. In induction motor drive, the flux and torque depend on the tator current value. Induction motor will have a imilar to that of a DC motor if the tator current component namely flux producing and torque producing current are eparately controlled. In vector control method, tator current both magnitude and phae angle are imultaneouly controlled. Vector control improve the dynamic performance of the Induction motor. During acceleration, deceleration and peed reveral of operation the motor, the peed and torque value are controlled with low ripple. But the vector control method ha ome drawback, uch a; it require two co-ordinate tranformation (Clark- Park tranformation and Invere Clark-Park tranformation), current controller for controlling torque producing current and flux producing current and high motor parameter enitivity. Thee drawback were eliminated in propoed DTC control method. DTC doen t require co-ordinate tranformation ytem and motor torque and flux value are directly calculated from the powerful

2 Direct Torque Control of Three Phae Induction Motor Uing Fuzzy Logic Speed Controller for Steady/Dynamic State Repone motor mathematical model. In thi propoed DTC method SV-PWM technique i ued for controlling the inverter output voltage magnitude and phae. Hyterei controller i employed for torque and flux control. The main feature of the DTC i imple tructure and good dynamic behavior. It improve the motor tatic peed accuracy, dynamic peed accuracy, torque repone and peed repone [1-4]. Fig. (a) Fig. (b) Fig.2. Propoed DTC cheme (a) Schematic diagram of propoed DTC Scheme. (b) Fuzzy Logic Speed Controller. III. CALCULATION OF AN ELECTROMAGNETIC TORQUE Fig.1. Variou control method of induction motor. II. PRINCIPLE OF OPERATION OF PROPOSED SCHEME The baic block diagram of DTC i hown in Fig.2. In DTC the actual parameter are controlled directly. Here the control variable are motor magnetizing flux and electromagnetic torque. Like a dc machine, Independent peed control and torque control i poible in thi cheme [5]. The fuzzy logic control i one of the controller in the artificial intelligence technique. Fig. 2(a) how the chematic model of the DTC of Induction Motor Drive (IMD) uing Fuzzy Logic Controller (FLC) baed PI controller for Speed ripple and torque ripple control. In thi project, Mamdani type FLC i ued and the DTC of IMD uing conventional PI- Speed controller require the precie mathematical model of the ytem and appropriate gain value of PI controller to achieve high performance drive. The three phae and two level VSI i hown in Fig.4, it ha a ix witche namely S1, S2 S6. Eight poible voltage pace vector (V0-V7) are achieved by uitable witching poition of the Inverter. In eight voltage pace vector, V1 to V6 i active voltage vector and V0, V7 are zero voltage vector [6-7]. In VSI, the witche S1, S2, S3 are called upper witche and S4, S5, S6 are called lower witche. When the upper part of witche i ON, then the witching value i 1 and when the lower witch i ON, then the witching value i 0 according to the combination of the witching mode are Sa, Sb, and Sc. Therefore, unexpected change in load condition would produce overhoot, ocillation of the IMD peed, long ettling time, high torque ripple, and high tator flux ripple. To overcome thi problem, a fuzzy control rule look-up table i deigned from the performance of torque repone of the DTC of IMD. According to the peed error and change in peed error, the proportional gain value are adjuted online a hown in Fig. 2(b). 2 nd International Conference On Emerging Trend in Engineering & Techno-Science (ETETS)-13 th Apr 2014 ISBN: Fig.3. Schematic diagram of voltage ource inverter(vsi). The inverter output voltage are calculated from the following equation V a = (Vdc/3) * [2Sa Sb -Sc] (1) V b = (Vdc/3) * [-Sa +2Sb -Sc] (2)

3 V c Direct Torque Control of Three Phae Induction Motor Uing Fuzzy Logic Speed Controller for Steady/Dynamic State Repone = (Vdc/3) * [-Sa Sb +2Sc] (3) In general, the tator voltage vector i written a in equation (1) V = (2/3) *V dc *(a + b *e j. (2П/3) + c *e j. (2 П/3) ) (4) Where, V dc i the dc link voltage of the inverter. The tator voltage and current i obtained from the following equation: V = V d + jv q i = i d + ji q (5) (6) The inverter three-phae voltage vector can be converted to tationary d-q axi with repect to tator frame by the following equation, V d = (2/3) Sa + (-1/3) Sb + (-1/3) Sc (7) V q = (0) Sa + (-1/ 3) Sb + (1/ 3) Sc (8) The tator flux i calculated from the actual equivalent circuit of an Induction Motor a follow: λ q = (V q R S.i q ) t (9) λ d = (V d R.i d ) t (10) λ = λ 2 2 q + λ d (11) And the tator and rotor flux linkage are λ = L I + I r L m (12) λ r = L r I r + I L m (13) The electromagnetic torque developed on the motor haft i the vector (cro) product of the tator flux and rotor flux linkage a follow Te = (3/2) * (P/2) * (λ r λ ) (14) That i the magnitude of torque can be written a Te = (3/2) * (P/2) * λ r λ Sin (15) Where i the angle between fluxe. The electromagnetic torque angle i given by = tan -1 (λ d / λ q ). But the etimation of the rotor flux i omewhat difficult. So the electromagnetic torque i calculated from the tationary d-q frame with repect to tator a follow: * T e T e * λ λ = Reference electromagnetic torque = Actual electromagnetic torque = Reference motor flux = Actual motor flux IV. SWITCHING OF AN INVERTER The tator rotating magnetic field poition can be determined by the proper inverter witching. There are eight poible witching poition achieved in the two level VSI fed Induction motor drive. Each witching of the inverter hift the magnetic field poition 60degree from the current poition. The witching poition ha a ix active voltage poition and two zero voltage poition. The eight poible witching poition can be obtained from the following waveform: Conider an Induction motor with three phae tar connected tator winding. Aume that the three phae inuoidal upply i fed from VSI to the tator winding with 120 degree phae hift irrepective of the frequency. Fig.5. Show the Stator Rotating Magnetic field poition baed on the inverter witching. When AC voltage i applied to the tator, the current flow through the phae winding. Depending upon the direction of current flow, the magnetic field i developed inide the tator. It aume that the poitive current flow through the phae winding A1, B1 and C1 reult in a north pole [8-10]. The Electromagnetic torque of the motor i expreed a Te = 1.5*(P/2)*(i d *λ q i q *λ d ) (16) P i no of pole. The gloary of ymbol i ummarized a follow: d, q = Stationary reference coordinate. V d,v q = Stator voltage in d-q coordinate. i d, i q = Stator current in d-q coordinate. i dr, i qr = Rotor current in d-q coordinate. λ d, λ q = Stator flux in d-q coordinate. λ dr, λ qr = Rotor flux in d-q coordinate. L, L r = Stator and rotor elf-inductance. L m = Mutual inductance. I m = Magnetizing current R, R r = Stator & rotor reitance. ω ref = Reference Rotor angular peed. ω actual = Actual Rotor angular peed. Fig.4.Three phae tator winding with VSI Table 1.Magnetic field for induction motor phae current 2 nd International Conference On Emerging Trend in Engineering & Techno-Science (ETETS)-13 th Apr 2014 ISBN:

4 Direct Torque Control of Three Phae Induction Motor Uing Fuzzy Logic Speed Controller for Steady/Dynamic State Repone The actual motor flux i compared with the reference flux value. The flux error value i given a input to the flux hyterei controller. Flux error = reference flux actual motor flux λ = λ * - λ (17) The flux error value i compared with the hyterei flux band width ( φ). The flux error value i maintained within the allowable hyterei flux band width limit. Fig.5. Rotating Magnetic Field (RMF) Table 2. Space Voltage Vector for inverter witching poition Hyterei flux acceptable error value φ = φ upper - φ lower The output action of the flux hyterei controller i given in the following table: Table 3. Flux hyterei comparator output State Flux Comparator output (φ) λ > φ 1 (Increae the flux) λ < - φ -1(Decreae the flux) V. DIRECT FLUX CONTROL Motor actual flux i etimated from the equation (9),(10) and (11): λ q = (V q R S.i q ) t (9) λ d = (V d R.i d ) t (10) λ = λ 2 2 q + λ d (11) 2 nd International Conference On Emerging Trend in Engineering & Techno-Science (ETETS)-13 th Apr 2014 ISBN: VI. DIRECT TORQUE CONTROL The torque hyterei comparator ha a three level output. The actual motor torque i compared with the reference torque value. The reference torque value i generated from the PI-Speed controller baed on the peed error value. Electromagnetic torque error value T e = T e * - T e (18) Torque hyterei comparator acceptable error value i T = T upper - T lower (19) The actual motor torque in-term of tator flux linkage i calculated from the equation (16): Te = 1.5*(P/2)*(i d *λ q i q *λ d ) (16) Torque angle (k) =tan -1 (λ d / λ q ) (20) The output action of the torque hyterei controller i given below in the table: Table 4.Torque hyterei comparator output State Torque Hyterei comparator output (T) T e > T 1 (Increae the torque) T < T e 0 (Torque at zero) <- T T e <- T -1(Decreae the torque) The voltage vector i elected baed on the output of the torque and flux hyterei controller. So that the motor flux and electromagnetic torque value are maintained contant. The three digit binary number repreent the witching poition of VSI. The digit give the value of Sa, Sb and Sc. The voltage vector election i tabulated below [11-12]

5 Direct Torque Control of Three Phae Induction Motor Uing Fuzzy Logic Speed Controller for Steady/Dynamic State Repone Table 5.Voltage vector election table Hyterei Voltage ector Selection (k) controller φ T (1) (2) (3) (4) (5) (6) VII. MATLAB SIMULATION RESULTS OF PROPOSED DTC SCHEME Speed Controller Simulink Subytem: (a) The DTC principle ha been imulated uing MATLAB/Simulink oftware. The Simulink model of the DTC cheme for SV-PWM VSI fed IM drive ha been preented in Fig. 6. The parameter of the induction motor in thi imulation are a follow: Rated motor power (P r ) = 2 kva Rated motor voltage (V r ) = 230 V AC Rated motor frequency (f r ) = 50 Hz Stator reitance (R S ) = mω Rotor reitance (R r ) = 9.2 mω Stator elf-inductance (L ) = mh Rotor elf-inductance (L r ) = mh Mutual Inductance (L m ) = mh Number of Pole (P) = 2 Moment of Inertia (J) = 3.1 kg*m 2 Friction Factor (F) = 0.08 N-m- Reference flux (λ * ) = 0.8 Wb (b) Fig.8. (a) Simulation ubytem diagram of fuzzy logic peed controller block (b) Fuzzy logic controller imulation ubytem Simulation Waveform of Propoed Scheme: (a) Fig.6. Simulation diagram of DTC baed three phae induction motor control technique DTC Subytem: (b) Fig.7. Simulation ubytem diagram of DTC block (c) 2 nd International Conference On Emerging Trend in Engineering & Techno-Science (ETETS)-13 th Apr 2014 ISBN:

6 Direct Torque Control of Three Phae Induction Motor Uing Fuzzy Logic Speed Controller for Steady/Dynamic State Repone (d) (i) Fig.9.Simulation reult (a) Motor three phae current when load torque i 100 Nm. (b) Motor three phae voltage when peed i 100 rpm. (c) Motor peed when et-peed i 500 rpm. (d) Motor torque when et-point load torque i 100 Nm. (e) Motor torque at 0 N-m et-point load torque. (f) Speed reveral from 100 rpm to -100 rpm. (g) Motor torque with different load torque et-point value and peed reveral operation. (h) Stator flux. (i) Stator flux trajectory. CONCLUSION (e) (f) In thi paper, an effective control technique i preented for direct flux and torque control of threephae Induction Motor. In thi propoed control technique the tatic PI-Speed controller i replaced by Fuzzy logic controller thereby reducing the tator flux and torque ripple. The two independent torque and flux hyterei band controller are ued in order to control the limit of the torque and flux. It i clearly een that the locu of the tator flux of propoed cheme i within the circle boundary created by ix active vector. Whenever there i a change of tator flux, the pace vector witching are uch choen that the flux error remain within the band of the controller. The imulation reult of propoed technique wa carried out for DTC of three-phae Induction Motor, the propoed control technique i uperior for good peed regulator, low tator flux linkage, and torque ripple under tranient and dynamic tate operating condition. REFERENCES [1] ABB Technical Uer Guide (g) [2] Baem EI Badi, Badii Bouzidi, and Ahmed Mamoudi (2013) DTC Scheme for a Four-Switch Inverter-Fed Induction Motor Emulating the Six-Switch Inverter Operation IEEE Tranaction on Power Electronic, Vol.28,No.7. [3] B.K.Boe, Modern Power Electronic and AC Drive, Prentice Hall Indic, (h) 2 nd International Conference On Emerging Trend in Engineering & Techno-Science (ETETS)-13 th Apr 2014 ISBN: [4] Brahim Metidji, N abil Taib, Lotfi Baghli, Toufik Tekioua and Seddik Bacha (2012) Low-Cot Direct Torque Control Algorithm for Induction Motor Without AC Phae Current Senor IEEE Tranaction on Power Electronic, Vol.27, No.9. [5] Curino Brandao Jacobina (2010) Single-Phae to Three- Phae Drive Sytem Uing Two Parallel Single-Phae Rectifier IEEE Tranaction on Power Electronic, Vol. 25.

7 Direct Torque Control of Three Phae Induction Motor Uing Fuzzy Logic Speed Controller for Steady/Dynamic State Repone [6] F. Blachke (1988) The principle of field-orientation a applied to the tranvector cloed-loop control ytem for rotating-field machine, Siemen Rev., Vol. 34, pp [7] G.S. Buja, M.P.Kazmierkowki (2005) DTC of pwm inverter-fed AC motor A Survey, IEEE Tran. on Ind. Elec., Vol. 54, No. 4. [8] Hatua, K, Ranganathan, V.T (2005) Direct Torque Control Scheme for Split Phae Induction Machine IEEE Tranaction on Indutry Application, Vol.41, No.5, pp [9] M.N. Uddin, T. S. Radwan, and M. A. Rahman (2002) Performance of fuzzy logic- baed indirect vector control for induction motor drive, IEEE Tran. Ind. Appl. Vol. 38, No. 5, pp [10] N. R. N. Idri, A. H. M. Yatim (2004) Direct torque control of induction machine with contant witching frequency and reduced torque ripple. IEEE Tran. on IE, Vol. 51, No. 4, pp [11] Weijie Lin, Zhuo zheng (2006) Simulation and Experiment of Senor le Direct Torque Control of Hybrid Stepping Motor baed on DSP Proceeding of the 2006 IEEE International Conference on Mechatronic and Automation Luoyang, China. [12] Yen-Shin Laui, Juo Chuin Lin (2003) New Hybrid Fuzzy Controller for Direct Torque Control Induction Motor Drive IEEE Tranaction on Power Electronic, Vol. 18, No.5, pp nd International Conference On Emerging Trend in Engineering & Techno-Science (ETETS)-13 th Apr 2014 ISBN: