SPACE VECTOR BASED DECOUPLED PWM TECHNIQUES FOR OPEN END WINDING INDUCTION MOTOR DRIVE

International Journal of Electrical Engineering & Technology (IJEET) olume 8, Issue 6, Nov-Dec 2017, pp. 16 28, Article ID: IJEET_08_06_003 Available online at http://www.iaeme.com/ijeet/issues.asp?jtype=ijeet&type=8&itype=6 ISSN Print: 0976-6545 and ISSN Online: 0976-6553 Journal Impact Factor (2016): 8.1891 (Calculated by GISI) www.jifactor.com IAEME Publication SPACE ECTOR BASED DECOUPLED PWM TECHNIQUES FOR OPEN END WINDING INDUCTION MOTOR DRIE M. Ranjit Assistant Professor, Department of Electrical & Electronics Engineering, NRJIET, Hyderabad, Telangana, India T. Bramhananda Reddy Professor &Head, Department of Electrical & Electronics Engineering, GPREC, Kurnool, Andhra Pradesh, India M. Suryakalavathi Professor, Department of Electrical & Electronics Engineering, JNTUH, Hyderabad, Telangana, India. ABSTRACT In this article, space vector based decoupled bus clamping PWM techniques are proposed for open-end winding induction motor drive (OEWIMD) fed with conventional two level inverters on either side. The switching vectors for the conventional inverters are generated using instantaneous reference voltages along with the simple digital logic. All the proposed bus-clamped PWM techniques are generated by phase shifting the one inverter reference phase voltages by 180 degrees with respect to the other inverter. A common-mode voltage is identified in the OEWIM drive. The entire space vector based decoupled bus clamping PWM techniques proposed in this work are to reduce the CM by greater extent and also give less switching loss compared to center spaced space vector PWM technique. The performance of all the proposed decoupled PWM techniques are explored both theoretically and experimentally and the corresponding results are presented. Key words: Bus clamping, Common-mode voltage (CM), Decoupled, Space ector Modulation, Open-end winding induction motor (OEWIM), Pulse width Modulation(PWM). Cite this Article: M. Ranjit, T. Bramhananda Reddy and M. Suryakalavathi, Space ector Based Decoupled PWM Techniques for Open End Winding Induction Motor Drive. International Journal of Electrical Engineering & Technology, 8(6), 2017, pp. 16 28. http://www.iaeme.com/ijeet/issues.asp?jtype=ijeet&type=8&itype=6 http://www.iaeme.com/ijeet/index.asp 16 editor@iaeme.com

M. Ranjit, T. Bramhananda Reddy and M. Suryakalavathi 1. INTRODUCTION To control the output voltage and frequency of two-level voltage source inverters various pulse width modulation techniques are used in past decade [1-4].These PWM techniques are categorized as sine PWM, space vector PWM(Center spaced PWM),bus clamping PWM and double switching clamping PWM techniques[1-6].in center spaced PWM, each phase switches uniformly at carrier frequency. In bus clamping PWM methods each phase is clamped to either positive or negative DC bus [6-8].In double switching bus clamped PWM, each phase is clamped over a period of time, along with that it is switched twice at the nominal carrier frequency [6-10]. These PWM techniques are differing in such a way that the switching vectors are employed in a half-carrier cycle (Ts). In center spaced PWM switching vectors starts with one null state and ends with one null state. In bus clamping PWM, only one null state is used in the given sub cycle [5-10].Whereas, in double switching bus clamping PWM uses the one null state like bus clamping PWM, but active state is switches twice in each half of carrier-cycle [5-10].Compared to center spaced PWM, bus clamping PWM techniques reduce the harmonic distortion in output voltage along with the reduction of switching losses of the inverter. [5-10].This paper report the decoupled space vector bus- clamping PWM techniques along with the center spaced space vector PWM technique for OEWIM drive. These PWM techniques are generated using instantaneous reference phase voltages.i.e reference voltages of one inverter are phase shifted by 180 degrees with respect to the other inverter phase voltages. These PWM techniques also reduce the CM by great extent, which is a common problem in conventional inverter. This proposed work is explored experimentally using dspace 1104 control board and the corresponding results are compared for different decoupled PWM techniques. 2. OPEN-END WINDING INDUCTION MOTOR (OEWIM) DRIE A schematic of symmetrical dual inverter fed OEWIM drive is shown in Figure.1.WhereRX, YX and BX denote the pole voltages of Inv-I and R X, Y X and B X denote the pole voltages of Inv-II. In this configuration, two conventional two level inverters are fed with separate dc supply of magnitude dc /2 to avoid the flow of common mode currents into the motor. Figure 1 Symmetrical dual inverter fed OEWIM drive The effective phase voltage of this configuration is given by Where Z=R, Y, B ZX Z' X' ZX Z' X' (1) http://www.iaeme.com/ijeet/index.asp 17 editor@iaeme.com

Space ector Based Decoupled PWM Techniques for Open End Winding Induction Motor Drive PWM techniques are generally used to control the output voltage and frequency of the inverters. But PWM inverters are usually operated with high frequency, which excite the parasitic capacitances of the machine leads to CM across the motor phases [11].Hence, the CM across the terminals X and X is given by XX' RR' YY' BB' (2) 3 The switching states of Inv-I and Inv-II are shown in Figure.2.When switch is on represented with + (or) 1, when switch is off represented with - (or) 0. (a) (b) Figure 2 Space vector locations of Inv-I (a) and Inv-II (b) To control the output voltage and frequency of inverters in proposed symmetrical OEWIM configuration space vector based decoupled PWM approach is used. 3. PROPOSED DECOUPLED PWM TECHNIQUES The basic principle involved in the proposed decoupled bus clamping PWM techniques along with the centre spaced PWM technique is to analyze and control the two conventional inverters feeding on either side of OEWIM independently. To achieve this one inverter is operating in one sector, whereas the other inverter is operated in advanced or delayed by 180 ο with respect to the other inverter. All the proposed decoupled bus clamping techniques gives minimum switching loss over centre spaced PWM technique and also reduce the CM by enormous level. Let the instantaneous reference voltages of Inverter-I and Inverter-II are given in Eq. (3) and Eq. (4) respectively. R1 Y1 B1 m COS ωt m COS ωt 120 ο m COS ωt & 240 ο (3) R2 Y2 m COS m COS ωt 180 ο ωt 120 ο 180 ο (4) http://www.iaeme.com/ijeet/index.asp 18 editor@iaeme.com

M. Ranjit, T. Bramhananda Reddy and M. Suryakalavathi B2 m COS ωt 240 ο 180 ο 3.1. Center Spaced PWM (8-1-2-7-7-2-1-8) In centre spaced PWM, zero vector is applied twice in a half carrier cycle [5]-[10].The number of switchings in a sub-cycle is equal to three [5]-[10]. From Fig.3, it can be observed that switching instants of the two inverters is not same. i.e, switching instants of the Inv- II(S1,S3,S5 ) are delayed in one half of sampling period, whereas the other half of the sampling period switching instants of the Inv-II are advanced compared to Inv-I switching instants(s1,s3,s5). It results in the generation of CM of magnitude +dc/6 & -dc/6 in one sampling period (2TS).The reason for the generation of CM in the OEW configuration is that each inverter is switching twice and also it results in the deviation of common mode voltage from the expected for a small instant of time [11], as shown in Fig.3. Figure 3 Switching combinations and common mode voltage profile of centre spaced PWM The other reason for variation of CM is due to the dead instant effects and also the variation in voltage raise and fall instants of a switch. This results the small bearing current can flow during the switching transitions [11].In centre spaced PWM, each phase is switches once in a sub-cycle and two sub cycles constitute a switching cycle. Therefore, average switching frequency fs=1 / 2*T S [4-10]. 3.2. Decoupled Bus Clamping PWM (812/721) In decoupled bus-clamping PWM techniques (812/721) only one null state is applied in a half carrier cycle. [5-10]. In these PWM techniques, one of the phase is clamped to either positive or negative DC bus and the corresponding switching vectors for the individual inverters are shown in Fig.4 and Fig.5.From Fig.4, it can be observed that for the bus clamping sequence 721 Inv-I switches in sector-i, whereas Inv-II switches 180 ο advance with respect to Inv-I. From Fig.5, it is also observed that for Inv-I R-phase is clamped to positive DC bus, whereas Y-phase and B-phase are switches once in a half switching cycle [6]-[10]. In case of Inv-II,Bphase is clamped to positive DC bus, R-phase switches once in a half carrier cycle. But, Y- phase having some delay in switching due to switch dead band effects and also delay in switch voltage raise and fall times [11]. http://www.iaeme.com/ijeet/index.asp 19 editor@iaeme.com

Space ector Based Decoupled PWM Techniques for Open End Winding Induction Motor Drive Figure 4 Switching sequences of the individual inverters using positive bus clamping PWM From Fig.6, it can be observed that for the bus clamping sequence 812 Inv-I switches in sector-i, whereas Inv-II switches 180 ο advance with respect to Inv-I like 721 sequence. From Fig.7, it is also observed that for Inv-I B-phase is clamped to negative DC rail, whereas Y- phase and R-phase are switches once in a half switching cycle [6]-[10]. Figure 5 Switching combinations and common mode voltage profile of positive bus clamping PWM Figure 6 Switching sequences of the individual inverters using negative bus clamping PWM In case of Inv-II, R-phase is clamped to negative DC rail, B-phase switches once in a half switching cycle. But, Y-phase is delayed by small instant of time. Both the bus clamping PWM techniques (721/812) phase-y is delayed, which results the generation of common mode voltage of magnitude ± dc/6 is shown in Fig.5 and Fig.7. http://www.iaeme.com/ijeet/index.asp 20 editor@iaeme.com

M. Ranjit, T. Bramhananda Reddy and M. Suryakalavathi Figure 7 Switching combinations and common mode voltage profile of negative bus clamping PWM 3.3. Decoupled Double Switching Bus Clamping PWM In decoupled double switching bus clamping PWM techniques, such as 7212,8121,2721,1812 each active state is switches twice in a half carrier cycle. Like other bus clamping techniques (721/812) only one null state is used in a half carrier cycle [6]-[10]. In sequence 7212, R- phase is clamped to positive DC rail, Y-phase is switches twice and B-phase is switched once in a half carrier cycle.[8]-[10].switching sequences of individual inverters and the common mode voltage profile of 7212 sequence is shown in Fig.8 and Fig.9. Figure 8 Switching sequences of the individual inverters using double switching positive bus clamping PWM From Fig.9, it can be observed that both in Inv-I and Inv-II Y-phase are switches twice in one sub-cycle. But, there will be a CM because of delayed response of the switches during transition from off to on and on to off state in Inv-II Y-phase. In sequence 8121, B-phase is clamped to negative DC rail, Y-phase is switches twice and R-phase is switched once in a half carrier cycle.[8]-[10].switching sequences of individual inverters and the common mode voltage profile of 8121 sequence is shown in Fig.10 and Fig.11. In case of the sequence 2721, R-phase is clamped to positive DC rail, Y-phase is switches once and B-phase is switches twice in a half carrier cycle [9-10]. Similarly, in sequence 1812 B-phase is clamped to negative DC rail, Y-phase is switches once and R-phase is switches twice in a half carrier cycle [9-10].Table-I shows the number of switchings of each phase over a half sampling period (T S ) in first sector. http://www.iaeme.com/ijeet/index.asp 21 editor@iaeme.com

Space ector Based Decoupled PWM Techniques for Open End Winding Induction Motor Drive Figure 9 Switching combinations and common mode voltage profile of double switching positive bus clamping PWM Figure 10 Switching sequences of the individual inverters using double switching negative bus clamping PWM Figure 11 Switching combinations and common mode voltage profile of double switching negative bus clamping PWM http://www.iaeme.com/ijeet/index.asp 22 editor@iaeme.com

M. Ranjit, T. Bramhananda Reddy and M. Suryakalavathi Table 1 Switching periods of decoupled pwm techniques S.No PWM Technique Sequence Switching Period(T S ) 1 Center-Spaced 8-1-2-7 T S 2 Negative Bus Clamping 8-1-2 2/3 T S 3 Positive Bus Clamping 7-2-1 2/3 T S 4 Double Switching Negative Bus Clamping 1-8-1-2 T S 5 Double Switching Positive Bus Clamping 2-7-2-1 T S 4. RESULTS AND DISCUSSION To validate the proposed configuration of OEWIM drive using space vector based decoupled PWM techniques, arious simulations are performed on open loop control of induction motor.to validate the same experimentally, a prototype model is developed, and the control signals for Inv-I and Inv-II are generated using dspace 1104 board. The switching frequency is chosen as 1 khz. The 9.2 KA inverters fed on either side of OEWIM (1HP, 415, 1.8A, 50 Hz) along with uncontrolled rectifiers on front end. A DC voltage of 255 is applied to each inverter. To get the various observations from the set a Digital Storage Oscilloscope (500 to 3.3) regulator is used. All the proposed decoupled PWM techniques shown in Table 1 are explored experimentally with modulation index (Mi) = 0.8. Figure.12(a) and (b), shows the effective phase voltage and R-phase stator current along with the CM of OEWIM drive using centre spaced PWM technique (8127).In this PWM technique, both zero states(7,8) are used in a half carrier cycle and also number of switchings per half carrier cycle is equal to three. This results the more harmonic distortion in the output voltage and more switching loss over bus clamping PWM techniques. The harmonic spectrum of phase voltage is shown in Figure.12(c).It is identified that a large amount of samples around the multiples of switching frequency (around 20) for a given switching frequency1000hz.with an effective DC voltage of 510 is applied to the proposed configuration results the maximum magnitude of effective phase voltage is at 2dc/3(340) and CM of magnitude± dc/6(85) is shown in Figure.12 (a) and (b). It can be observed from Figure.13 (a), (b) and(c) & Figure.14 (a), (b) and (c), that the quality of effective phase voltage is improved over centre spaced PWM technique. This is due to the number of switchings per half carrier cycle is reduced in bus clamping PWM (812/721) than centre spaced PWM, which results the switching loss is reduced approximately by 33.33% over centre spaced PWM [10].In bus clamping PWM techniques one of the phase is clamped to either positive dc bus or negative dc bus, which results the reduction in switching loss. From Figure.13(c) and Figure.14(c), it is observed that the CM of magnitude ±dc/6(85) is maintained same as centre spaced PWM. In double switching bus clamping PWM techniques(2721/1812),one of the active state is switches twice unlike in center spaced PWM. It results the one of the phase is switches twice in a half carrier cycle (Ts), so that the improvement in effective phase voltage is shown in Figure.15 (a) and Figure.16 (a).but the CM magnitude is increased (± dc/3(170)) over center spaced PWM and bus clamping PWM techniques shown in Figure.15(b) and Fig.16(b). http://www.iaeme.com/ijeet/index.asp 23 editor@iaeme.com

Space ector Based Decoupled PWM Techniques for Open End Winding Induction Motor Drive (c) Figure 12 a)effective phase voltage and R-phase stator current b) CM c) Harmonic spectra of effective phase voltage with center spaced PWM at fs=1000hz. (c) Figure 13 a)effective phase voltage and R-phase stator current b) CM c) Harmonic spectra of effective phase voltage with negative bus clamping PWM at fs=1000hz. http://www.iaeme.com/ijeet/index.asp 24 editor@iaeme.com

M. Ranjit, T. Bramhananda Reddy and M. Suryakalavathi (c) Figure 14 a)effective phase voltage and R-phase stator current b) CM c) Harmonic spectra of effective phase voltage with positive bus clamping PWM at fs=1000hz. (c) Figure 15 a)effective phase voltage and R-phase stator current b) CM c) Harmonic spectra of effective phase voltage with double switching negative bus clamping PWM at fs=1000hz. http://www.iaeme.com/ijeet/index.asp 25 editor@iaeme.com

Space ector Based Decoupled PWM Techniques for Open End Winding Induction Motor Drive (c) Figure 16 a)effective phase voltage and R-phase stator current b) CM c) Harmonic spectra of effective phase voltage with double switching positive bus clamping PWM at fs=1000hz. (c) Figure 17 a)effective phase voltage and R-phase stator current b) CM c) Harmonic spectra of effective phase voltage with proposed decoupled PWM techniques at fs=1000hz. http://www.iaeme.com/ijeet/index.asp 26 editor@iaeme.com

M. Ranjit, T. Bramhananda Reddy and M. Suryakalavathi The corresponding harmonic spectrum is shown in Figure.15(c) and Figure.16(c).It observed that the harmonic samples around the switching frequency is less than in center spaced PWM and bus clamping PWM. It is also observed that as the CM magnitude increases in effective phase voltage, the quality of waveform is also improved. Hence, out of all proposed PWM techniques double switching bus clamping techniques are superior to other proposed techniques. From Figure.17(c), it is identified that the CM magnitude is reduced to zero. This is possible if the Inv-II phase voltages are phase shifted by 120 ο with respect to Inv- I phase voltages. Though CM is nullified completely, but the quality of effective phase voltage becomes poor as shown in Figure.17 (a) and(c). 5. CONCLUSIONS Decoupled space vector based bus clamping PWM techniques are proposed for OEWIM drive fed with two conventional inverters on either side. All the proposed PWM techniques are generated using the instantaneous reference phase voltages of the inverters. That is, Inv-I is operated in sector-i, while Inv-II is operated in sector-i (180 ο ).In all the PWM techniques except some double switching bus clamping sequences [2721, 1812] common mode voltage magnitude is reduced to ± dc/6.in case of the sequences [2721, 1812] it is around± dc/3.but, output voltage wave form is improved over remaining PWM techniques. Out of all proposed PWM techniques bus clamping PWM techniques gives less switching loss. This is because of number of switchings in these PWM techniques is only two in a half carrier cycle unlike other proposed PWM techniques. REFERENCES [1] J. Holtz, Pulse width modulation for electronic power conversion, Proc. IEEE, vol. 82, no. 8, pp. 1194 1214, Aug. 1994. [2] A. M. Hava and E. Un, Performance analysis of reduced common-mode voltage PWM methods and comparison with standard PWM methods for three- phase voltage-source inverters, IEEE Trans. Power Electron., vol. 24, no. 1, pp. 241 252, Jan. 2009. [3] A. M. Hava, R. J. Kerkman and T. A. Lipo, Simple analytical and graphical methods for carrier-based PWM-SI drives, IEEE Trans. Power Electron., vol. 14, no. 1, pp. 49-61, Jan. 1999. [4] G. Narayanan, H. K. Krishnamurthy, Di Zhao and R. Ayyanar, Advanced bus-clamping PWM techniques based on space vector approach, IEEE Trans. Power Electron., vol. 21, no. 4, pp. 974-984, Jul. 2006. [5] H. Krishnamurthy, G. Narayanan, R. Ayyanar and. T. Ranganathan, Design of spacevector based hybrid PWM techniques for reduced current ripple, in Proc. IEEE-APEC 03, Miami, Florida,pp. 583-588, Feb. 2003. [6] S.Das and G. Narayanan, Novel switching sequences for a space-vector modulated threelevel inverter, IEEE Trans. Ind. Electron., vol. 59, no.3, pp. 1477 1487, Mar. 2012. [7] A. R. Beig and. T.Ranganathan, Space vector based bus clamped PWM algorithms for three level inverters: Implementation, performance analysis and application considerations, in Proc. IEEE Appl. Power Electron.Conf. Expo, Feb. 2003, vol. 1, pp. 569 575. [8] G. Narayanan, D. Zhao, H. K. Krishnamurthy, R. Ayyanar, and. T. Ranganathan, Space vector based hybrid PWM techniques for reduced current ripple, IEEE Trans. Ind. Electron., vol. 55, no. 4, pp. 1614 1627, Apr.2008. http://www.iaeme.com/ijeet/index.asp 27 editor@iaeme.com

Space ector Based Decoupled PWM Techniques for Open End Winding Induction Motor Drive [9] Soumitra Das,G. Narayanan and M.Pandey Space vector based hybrid Pulse width Modulation techniques for a Three- Level inverter IEEE Trans. Power Electron.,vol.29,no.9,pp.4580-4591,Sep.2014. [10].S.S.Pavan Kumar Hari and G. Narayanan space-vector based hybrid PWM technique to reduce peak-to-peak Torque ripple in Induction motor Drives IEEE Trans. Ind. Applica, vol.52, no.2, pp.1489-1499, Apr.2016. [11] J. Kalaiselvi and S. Srinivas, Bearing Currents and Shaft oltage Reduction in Dual- Inverter-Fed Open-End Winding Induction Motor With Reduced CM PWM Methods in IEEE Trans. Ind. Electron, ol. 62, No. 1,pp-144-152, January 2015. [12] Khichada Bhavin A, K.J. Chudashma, yas Darshan M and Shiyal Jignesh D, 3- Phase Induction Motor Parameter Monitoring and Analysis Using Labview. International Journal of Electrical Engineering & Technology, 7(6), 2016, pp. 81 91. [13] Raichel Mathew, Aswathy Mohandas P, A Bridgeless CUK Converter Based Induction Motor Drive For PFC Applications, International Journal of Electrical Engineering & Te chnology, 5(12), 2014, pp. 191 196 [14] Sijitha Issac, Dr. Poorani S and Dr. M Jayan. Advancement of Imperialist Competitive Algorithm for the Design of Low Speed Single Sided Linear I nduction Motor. International Journal of Electrical Engineering & Technology, 8(1), 2017, pp. 72-79 http://www.iaeme.com/ijeet/index.asp 28 editor@iaeme.com