163

Proc. of Int. Conf. on Control, Communication and Power Engineering 2010

Performance Comparison Of Multi-Level Inverter Fed Induction Motor Drive G.Durgasukumar1, M.K.Pathak2, S.P.Srivastava2 1

Electrical Engineering Department, IIT Roorkee, India Email: durgadee@iitr.ernet.in {mukesfee, satyafee}@iitr.ernet.in

Abstract— Multi-level inverter has emerged as an important topology in the area of high power-medium voltage energy control applications due to their good harmonic rejection capability. This paper presents the application of simplified space vector pulse width modulation (SVPWM) method for three-level, five-level and seven-level diode clamped inverters feeding a threephase Induction motor. This paper compares total harmonic distortion values of voltage waveforms of Induction motor to the conventional two-level inverter drive using diode clamped multi-level inverter (Three, five and seven level).

inverter has presented. This method cannot identify the sector containing the reference space vector.

Although these methods propose general SVPWM algorithms for multilevel inverter, the coordinate transformations used in these algorithms are somewhat complicated. In [9], a new simplified space vector pulse width modulation (SVPWM) method for three-level inverter is proposed. In [10-11], a new 3-D SVM in natural coordinates is applied to conventional four-leg voltage source converters showing the advantages of using these coordinates. In [12-13], a novel threedimensional (3-D) space-vector algorithm for four-leg multilevel converters is presented. This technique greatly simplifies the selection of the 3-D region where a given voltage vector is supposed to be found. In this paper, a simple SVPWM method for three-level, above three-level inverter and comparison of total harmonic distortion presented. By using the new SVPWM strategy, effective time calculation and switching sequence selection are easily done like conventional two-level inverter. Simulation studies are carried out using 3-Phase, 50HP, 400V, 50Hz, and 1500RPM induction machine.

Index Terms— Multi-level inverter, SVPWM, Three-level inverter, Five-level inverter, Seven-level inverter, Induction motor, Total harmonic distortion (THD).

I. INTRODUCTION In high power applications, the switching frequency of the power device has to be restricted below 1 KHz unlike in conventional two level due to the increased switching losses and also the level of dc-bus voltage[1].

Many researchers have worked on the space vector modulation of multilevel inverters [2]-[11]. In [2], a method of SVPWM for high level inverters that represents output vector in three-dimensional Euclidean space is presented. The method is based on the fact that increasing the number of levels by one always forms an additional hexagonal ring. In [3], the hexagon representing space vector diagram is flatten and the reference voltage vector is normalized in order to reduce computations of the algorithm. In [4], a SVPWM with a predictive current control loop have presented. In the current error is calculated and the switching state is selected when the value of the error is less. In [5], a space vector modulation allows reduction in the inverter output voltage distortion due to turn-off, turn-on and dead times.

In [6], a simple space vector pulse width modulation algorithms for a multilevel inverter for operation in the over-modulation range have presented. In [7], a relationship between space-vector modulation and carrier-based pulse-width modulation for multilevel inverter has presented. In [8], a generalized method of space vector pulse-width modulation for multilevel

II. SIMPLIFIED SVPWM FOR MULTI LEVEL INVERTER A. Basic principle The space-vector diagram of any multi-level inverter is composed of six hexagons, which can be reduced insteps further into the space-vector diagrams of conventional two-level inverters. The space vector diagram three-level inverter and its two level hexagons are shown in Fig. 3(a) and 3(b). A multi-level spacevector plane is transformed to the two-level space-vector plane by using the two steps.

1) From the location of a given reference voltage, one hexagon has to be selected.

2) The original reference voltage vector has to be subtracted by the amount of the center voltage vector of the selected hexagon.

Determination of switching sequence and the calculation of the voltage vector duration time is done as in conventional two-level SVPWM method.

242 © 2009 ACEEE

Proc. of Int. Conf. on Control, Communication and Power Engineering 2010

ib(Amp)

ia(Amp)

Te(N-m)

Speed(RPM)

2) Performance parameters of induction motor

ic(Amp)

Fig. 3 Space vector diagram of three-level inverter, six twolevel hexagons and Change base vector of original reference voltage vector in three level

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Fig. 6 Two level inverter fed induction motor performance parameters

B. Correction of reference voltage vector By the location of a reference voltage vector, one hexagon is selected among the six small hexagons that comprise the multi-level space-vector diagram. The reference voltage vector should lie in the inner of the selected hexagon. This procedure divides the multi-level space-vector diagram into six regions that are covered by each small hexagon. If the reference voltage vector stays in the regions that are overlapped by adjacent small hexagons, the multi-level space-vector diagram can have multiple values that are possible. Once the value is determined, the origin of a reference voltage vector is changed to the center voltage vector of the selected hexagon. This is done by subtracting the center vector of the selected hexagon from the original reference vector, as shown in Fig.3(c). Similar procedure is adapted for more than three- level also.

In calculating the effective times, the only difference between the two-level SVPWM and the multi-level (Three, five and seven level) SVPWM is multiplying factor 2 ,4 and 6 appears respectively.

B.Multi-level inverter fed induction motor Fig. 7 shows the simulink model of Multi-level inverter fed induction motor drive. The corresponding line-line voltages Fig. 8 to Fig. 10 and the performance parameters of multi-level inverter fed induction motor for three, five and seven-level are shown in Fig. 11 respectively.

C.

Fig. 7 Multi-level inverter circuit fed induction motor simulink model

III. SIMULATION RESULTS

Three-level inverter fed induction motor drive

A. Two-level inverter fed induction motor Fig.4 shows the simulink model of two-level inverter fed induction motor drive. The corresponding line voltage and the performance parameters speed, torque (Te) and currents (ia, ib, ic) are shown in Fig. 5 and Fig. 6 respectively.

Line-Voltage

Fig. 8 Three -level inverter line voltage

D. Five-level inverter fed induction motor

Line voltage Fig. 4 Two-level inverter circuit fed induction motor simulink model

1) Line-Voltage

Fig. 9 Five -level inverter line-line voltages Fig. 5 Two-level inverter line voltage

243 © 2009 ACEEE

Proc. of Int. Conf. on Control, Communication and Power Engineering 2010

REFERENCES

E. Seven-level inverter fed induction motor Line voltage:

[1] X. Wu, Y. Liu, and L. Huang, “A Novel space vector modulation algorithm for three-level PWM voltage source inverter,” in Proc. IEEE Conf. Computers, Communications, Control and Power Engineering, Vol. 3, pp. 1974–1977, Oct. 2002.

[2] N. Celanovic and D. Boroyevich, “A fast space-vector modulation algorithm for multilevel three-phase converters,” IEEE Trans. Ind. Appl., vol.37, pp.637641, 2001.

[3] M.M. Prats, R. Portillo, J.M. Carrasco, and L.G. Franquelo, “New fast space-vector modulation for multilevel converters based on geometrical considerations,” in Proc. 28th Annual Conf. Industrial Electronics Society, Vol. 4, pp. 3134–3138, Nov. 2002.

[4] G.S. Perantzakis, F.H. Xepapas and S.N. Manias, “ Efficient predictive current control technique for multilevel voltage source inverters,” in Proc. 11th EPE European Conf. Power Electronics and Applications, Dresden, 2005.

[5] C.Attainese, V.Nardi, and G.Tomasso, “Space vector modulation algorithm for power losses and THD reduction in VSI based drives,” Electrical power components and systems, vol.35, pp.1271-1283, 2007.

[6] Amit Kumar Gupta and Ashwin M. Khambadkone,” A General Space Vector PWM Algorithm for Multilevel Inverters, Including Operation in Over-modulation Range,” IEEE Trans. power. Electron., vol. 22, pp.517526, March 2007.

[7] Wenxi Yao, Haibing Hu, and Zhengyu Lu, “ Comparisons of space-vector modulation and carrierbased modulation of multilevel inverter,” IEEE Trans.

Power. Electron., vol. 23, pp.45-51, Jan.2008.

[8] Aneesh Mohamed, A.S.Anish Gopinath, and M.R.Baiju, “A simple space vector pwm generation scheme for any general n-level inverter,” IEEE Trans. Ind. Electron., vol. 56, pp.1649-1656, May 2009.

[9] Jae Hyeong Seo, Chang Ho Choi, and Dong Seok Hyun, “A new simplified space–vector pwm method for threelevel inverters,” IEEE Trans. Power. Electron., vol. 16, pp.545-550, july 2001.

[10] M. A. Perales, M. M. Prats, R. Portillo, and L. G. Franquelo, “Threedimensional space vector modulation in abc coordinates for four-leg voltage source converters,” IEEE Power Electron. Lett., vol. 1, no. 4, pp. 104–109, Dec. 2003.

[11] G. Narayanan and V. T. Ranganathan, “Extension of operation of space vector PWM strategies with low switching frequencies using different overmodulation algorithms”, IEEE Trans. Power Electron., Vol.17, pp.788 -789, Sept. 2002.

[12] Leopoldo Garcia Franquelo, Ma. Ángeles Martín Prats, “ Three-Dimensional Space-Vector Modulation Algorithm for Four-Leg Multilevel Converters Using abc Coordinates”, IEEE Trans. Ind. Electron , vol. 53, no. 2, pp.458-466, April 2006.

[13] Yuen Fong Chan, M. Moallem and Wei Wang, ₃ Design and implementation of modular FPGA based PID controllers₄ , IEEE Trans. Ind. Electron. , vol.54, no.4, pp.1898 ⁺1906, Aug. 2007.

Fig. 11 Seven-level inverter line-line voltages

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F. Performance parameters of multi-level inverter fed induction motor 2000 0 -2000

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Fig. 12 Multi-level inverter fed induction motor performance parameters

IV. COMPARISON OF %THD TABLE .1 INVERTER LINE VOLTAGES

Parameters

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3 Level

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7 Level

Vab Vbc Vca

14.16% 13.29% 14.85%

3.91% 4.93% 4.54%

1.50% 0.84% 1.40%

1.41% 0.83% 1.32%

V. CONCLUSIONS A comparative study on THD of output line-line voltage and current waveforms of two-level, three-level, five-level and seven-level three-phase diode clamped inverters has been presented in this paper using simplified space vector modulation technique. It has been observed that as the level of inverter increases there is an improvement in the performance of induction motor compared to the conventional two-level inverter.

The THD of line-line voltages and phase currents decreases with the increase in number of levels of inverter.

ACKNOWLEDGEMENT The help and support of Mr.Abhiram and Mr.V.Karthik during the course of this work is acknowledged.

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