 Open Access
 Total Downloads : 625
 Authors : Preetha.S.L, J. Merry Geisa
 Paper ID : IJERTV2IS90357
 Volume & Issue : Volume 02, Issue 09 (September 2013)
 Published (First Online): 12092013
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
A New PWM Generation Scheme for Multi Level Inverter
space vector is move along with circular trajectory. In general, the SVPWM implementation involves the sector identification, switchingtime calculation, switchingvector determination, and optimum switchingsequence selection for the inverter voltage vectors.[12][13].
This paper proposes a new approach to generate SVPWM signals for multilevel inverters. The
space vector is move along with circular trajectory. In general, the SVPWM implementation involves the sector identification, switchingtime calculation, switchingvector determination, and optimum switchingsequence selection for the inverter voltage vectors.[12][13].
This paper proposes a new approach to generate SVPWM signals for multilevel inverters. The
International Journal of Engineering Research & Technology (IJERT)
ISSN: 22780181
Vol. 2 Issue 9, September – 2013
Preetha.S.L 1
M.E Student, Dept. of EE, St.Xaviers Catholic College of Engineering , Nagercoil, Tamil Nadu
J. Merry Geisa 2 ,
Assistant Professor Dept. of EEE, St.Xaviers Catholic College of Engineering , Nagercoil, Tamil Nadu
Abstract
This paper proposes new SVPWM technique has been presented for multilevel inverters. It is a generalized method for the generation of space vector pulse width modulation (SVPWM) signals for multilevel inverters. The switching vectors and optimum switching sequence are automatically generated by the principle of mapping. In the proposed method, the actual sector containing the tip of the reference space vector need not be identified. A method is presented to identify the center of a sub hexagon that contains the tip of the reference space vector. Using the center of the sub hexagon, the reference space vector is mapped to the inner sub hexagon, determination of the duration of switching vectors and optimum switching sequence corresponding to a twolevel inverter is determined. The twolevel vectors are translated to the vectors of the multilevel inverter by the principle of reverse mapping proposed in this paper. Switching vectors of the multilevel inverter by adding the center of the Sub hexagon to the two level vectors. The proposed method can be extended to any multilevel inverter. The scheme is explained for three level and results are presented for three level with and without load conditions.
Key wordsMultilevel inverter, reverse mapping, space vector pulse width modulation (SVPWM),Switching sequence, Candidate vector.
1.Introduction
The most widely used techniques for implementing the pulse width modulation (PWM) strategy for multilevel inverters are sinetriangle and space vector PWM (SVPWM).In the SVPWM [1][2] scheme
reference space vector is rotated ,tip of the voltage
Proposed method uses sector identification only at the twolevel. In the proposed method, the actual sector (where the tip of the instantaneous reference space vector lies) in the space vector diagram of a multilevel inverter [9] is not required to be identified. A method using the principle of mapping is proposed for generating the switching vectors corresponding to the actual sector and the optimum switching sequence of a multilevel inverter from that of the twolevel inverter. An algorithm is proposed for generating SVPWM for any multilevel inverter. The proposed method can be used for an inverter with an even number of levels also. The scheme is explained with a threelevel inverter, and simulation results for threelevel and the current wave forms of three level under load condition are presented.
II. Principle Of The Proposed Method
Fig. 1shows the space vector diagram of three level inverter. The small triangles formed by the adjacent voltage space vectors are called sectors. Such six sectors around a voltage space vector forms a hexagon called sub hexagon [3]. Fig.1 consist of two subhexagons. The are represented as subhexagonI(referred as inner sub hexagon) having the vector 000 as the center and subhexagonII having the vector 110 as center The inner sub hexagon can be viewed as a space vector diagram of a two level inverter whose inverter voltage vectors switch between the lower most levels.
Subhexagon1 can be also viewed as a space vector diagram of a twolevel inverter [3][5],[7], whose voltage vectors involve higher levels. The shifting of subhexagon11 in the space vector diagram of multilevel inverter towards zero vectors 000 involves
the mapping of the sectors of sub hexagon II to the sectors of the inner sub hexagon. This is done by subtracting the vector at the center of subhexagonII from its other vectors .Consider voltage space vectors 000, 001, 101, and 111 associated with sector 5 of inner sub hexagon and voltage space vector 010
inner sub hexagon, by adding these vectors with the vector located at the center of the sub hexagon, the actual switching vectors 220,210,200 for the reference space vector can be generated
which is the vector at sub hexagonal. Adding 010 to the voltage space vector associated with sector5 of the inner sub hexagon gives the vectors 010 (000+010), 011(001+010), 111(101+010) which are
100+100=200
B
020
120
2 T
3
220 C
1
the vectors associated with sector 5 of sub hexagon
010+010=020 010 110o

The mapping of the inner sub hexagon to any other sub hexagon is used to generate the vectors
001+001=002
4 T 6
2 5
210
associated with any sector in the space vector diagram of the threelevel inverter.
.
3
A 011
4
000 1
O
111 6
100
200
A
020 120
220
5
001
101
010
021
110
210
002 B
C
022
012
011
000
111
222
001 101
100
201
200
Fig.2. Generating switching vectors through reverse mapping

Identifying The Center Of Subhexagon
s2
020 120
220
002 102
202
s3 021
010
110
s1
210
Fig. 1. Space vector diagram of Threelevel inverter
Fig. 2 shows the instantaneous space vector OT. The tip of the reference space vector OT lies in the sector I of the sub hexagon II which contains the tip of the reference space vector. The vector 110 at the center of the sub hexagon III which contain the tip of the reference space vector. The vectors 000,100, and110
022
012
s4
011
002
000
111
222
001 101
102
s5
100
202
201
s6
200
are associated with sector I of the inner sub hexagon. Subtracting the center of the sub hexagon II to the
Fig. 3.: Layers in the space vector diagram of threelevel inverter
Fig.3.also shows the six 60 regions S1, S2, S3, S4, S5, and S6.In this paper, these candidate vectors are automatically generated from the vectors of the inner subhexagon, and the candidate vector which is closest to the tip of the reference space vector is chosen as the center of the sub hexagon.
A.Identifying the layer of operation
The instantaneous reference space vector can be resolved into the axes, ja, jb, and jc. Where va,vb, and vc are the instantaneous amplitudes of the three reference phase voltages
Vja=3/2(vavc) (1)
Vjb=3/2(vbva) (2)
B.Generating Candidate Vectors for the Sub hexagon Center
Let the vectors on the inner side of layer 2 for any 60 region be (a1, b1, c1) and (a2, b2, c2) and the end vectors on theinner side of layer m be (am1, bm1, cm1) and (am2, bm2, cm2). Then, the end vectors on the inner side of layer m can be generated as
(am1, bm1, cm1) = (m 1) Ã— (a1, b1, c1)
(am2, bm2, cm2) = (m 1) Ã— (a2, b2, c2) (5)
Vjc=3/2(vcvb) (3)
Let vjmax be the maximum magnitude among the three resolved components. It may be noted that the
2*(a2,b2,c2) 020
120
L2
220 2*(a1,b1,c1)
width of each layer in the case of an nlevel inverter is ( (3/2) (Vdc/(n1)). Therefore, the layer number can be easily obtained as in Fig.4
m=1+int(Vjmax/(3/2Vdc/(n1))) (4)
(a2,b2,c2)
010
110 (a1,b1,c1)
L1
vref
(110)(100)=010 110+010=120
vc
Vb 220
000
100

JB
020
010
L2 T
110
L1
JA 3/2
3/2
( am1,bm1,cm1) = (m1)(a1,b1,c1 )
(am2,bm2,cm2) =( m1)(a2,b2,c2)
va
022
011
001
0 000
101
100
200 Va
=(a2,b2,c2)(a1,b1,c1)
Fig.5. : Generating candidate vectors for the center of the sub hexagon
If (a0, b0, c0) is the instantaneous switching vector
002 202
Vc JC
vb
corresponding to the twolevel inverter and (ac, bc, cc) is the vector at the center of the sub hexagon, then the actual switching vector of the multilevel inverter is explained in Fig 6
Fig.4. ja,jb and jc axis and width of each layer for three level inverter
(am, bm, cm) =(a0, b0, c0) +(ac, bc, cc) (6)
B
120
2 T
220 C
V.Results And Discussion
3 1
010 110o
210
2
2
4 T 6 di
5
3
A 011
4
000 1
O
111 6
5
100 A
001
C
101
B
Fig 7: Pole voltage waveforms of three level inverter
Fig 6: reverse mapping


Control Of Induction Motor
The speed control of the induction motor has evolved over the years from the simple stator voltage control where in the stator voltage is varied to achieve a small speed range. How ever the stator voltage control is very inefficient as the flux decrease with decrease in voltage. The generated torque is the product of the flux and the stator current. If the flux decreases with reduction in stator voltage, the generated torque reduces. Next in the evolution of the induction motor control is the flux control. Depending on the type of the flux control , where based on the steadystate flux control, the scalar(v/f) control and the vector control strategies has evolved.
Fig. 8: Instantaneous duty ratio three level inverter for modulation index .5
Fig 9: Three phase current Va,Vb,Vc
Fig 9. Shows the three phase voltages obtained by the application of current control scheme.
CONCLUSION
The work brings out direct and simple approach to generate space vector PWM (SVPWM) for multilevel inverter. The switching vectors and switching sequence are automatically generated by the principle of mapping. The vector at the center of the sub hexagon containing reference space vector was directly identified, The reference space vector is mapped to the innermost sub hexagon and switching vectors for the two level inverters are generated. The two level inverter vectors are translated to multilevel inverter vectors by the principle of reverse mapping. The algorithm does not require any lookup table nor any complex mapping technique to generate a SVPWM. The algorithm can be extended to any general multilevel inverter without any complexity. The algorithm has been simulated in a MATLAB/SIMULINK for threelevel, and validate the performance of the algorithm driven under load condition. Current wave form of the given load condition is presented here.
REFERENCES

WenxiYao, Haibing Hu, and Zhengyu LuComparisons of SpaceVector Modulation and CarrierBased Modulation of Multilevel InverterIEEE transactions on power electronics, vol. 23, no. 1, pp.4551,2008.

E. G. Shivakumar, K. Gopakumar, S. K. Sinha,

Pittet, and V. T. Ranganathan Spacevector PWM control of dual inverter fed openend winding induction motor drive, in Proc. IEEE APEC, 2001, pp. 399405,2001.


B. P. McGrath, D. G. Holmes, and T. Lipo
Optimized spacevector switching sequences for multilevel invertersIEEE Trans. Power Electron., vol. 18, no. 6, pp. 12931301,2003.

A. Gopinath, A. Mohamed A. S., and M. R. BaijuFractal based spacevector PWM for multilevel inverters A novel approachIEEE Trans. Ind. Electron., vol. 56, no. 4, pp. 1230.1237,2009.

K. Zhou and D. WanRelationship between spacevector modulation and threephase carrier based PWM: A comprehensive analysis IEEE Trans. Ind. Electron., vol. 49, no. 1, pp. 186.196,2002.

A. K. Gupta and A. M. KhambadkoneA general spacevector PWM algorithm for multilevel inverters, including operation in over modulation rangeIEEE Trans. Power Electron., vol. 22, no. 2, pp. 517526,2007.

J. Rodriguez, J.S. Lai, and F. Z. PengMultilevel inverters: A survey of topologies, controls, and applicationsIEEETrns. Ind. Electron., vol. 49, no. 4, pp. 724738,2002.

BlaskoVAnalysis of a hybrid PWM based on modified spacevector and trianglecomparison methods Industry Applications, IEEE Transactions on Volume:33, PP.75676,1997.

Amit Kumar Gupta, and Ashwin M. Khambadkone A Space Vector PWM Scheme for Multilevel Inverters Based on TwoLevel Space Vector PWMIEEE transactions on industrial electronics, vol. 53, no. 5, pp.1631 1639,2006.

Sifat Shah, A. Rashid, MKL Bhatti(2012) Direct Quadrate (DQ) Modeling of 3Phase Induction Motor Using MatLab / Simulink. Canadian Journal onElectrical and Electronics Engineering Vol. 3, No. 5.

Emmanuel delaleau, JeanPaul Louis,Romeo Ortega(2001) modeling and controlof induction motors,Int. J. Appl. Math. Comput. Sci, Vol.11, No.1, 105129.

E.G.Shivakumar, K. Gopakumar, S. K. Sinha, A. Pittet, and V. T. Ranganathan,(2001) Space vector PWM control of dual inverter fed open endwinding induction motor drive,in Proc. IEEE APEC, 2001, pp. 399405 [14]