 Open Access
 Total Downloads : 17
 Authors : Saikat Majumdar, Ravi Raushan, Bidyut Mahato, Kartick Chandra Jana, Parashuram Thakura, Shio Kumar Singh
 Paper ID : IJERTCONV4IS02002
 Volume & Issue : CMRAES – 2016 (Volume 4 – Issue 02)
 Published (First Online): 24042018
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Comparative Study of Space Vector Pulse Width Modulation based TType Threelevel Inverter
Saikat Majumdar Dept. of Electrical Engg. ISM DHANBAD, INDIA
Ravi Raushan Dept. of Electrical Engg. ISM DHANBAD, INDIA
Bidyut Mahato Dept. of Electrical Engg. ISM DHANBAD, INDIA
Kartick Chandra Jana Dept. of Electrical Engg ISM DHANBAD, INDIA
Parashuram Thakura Dept. of Electrical Engg. BIT Mesra, Ranchi, INDIA
Shio Kumar Singh Chief, Capability Development TATA STEEL, JAMSHEDPUR
AbstractA threephase Ttype threelevel inverter configuration is demonstrated. Analysis of suggested threelevel inverter has been presented. An improved threelevel space vector pulsewidth modulation technique, which utilize the state redundancies has been explained and verified over recommended threelevel inverter and neutral point clamped inverter under linear range of operation. Modelling and simulation of Ttype threelevel inverter using presented space vector pulse width modulation is carried out in MATLAB/SIMULINK environment and results are presented. Proposed inverter is also compared with other configurations.
Keywords Space vector pulse width modulation; Ttype Inverter; total harmonic distortion; multilevel inverter.

INTRODUCTION
Multilevel inverter (MLI) was first introduced by Baker and Bannister in the year 1975 [12]. It came after the limitations of twolevel inverter such as higher total harmonic distortion (THD), high switching frequency, high dv/dt losses, higher commutation problem and higher rating devices. Multilevel inverter can produce any desired higher output voltage by incorporating small DC sources. Application of multilevel inverter includes industrial drive control, renewable energy system, HVDC, STATCOM etc. [37].
Some early introduced multilevel inverters such as Cascaded Hbridge (CHB) [2], Neutral Point clamped (NPC)

and Flying Capacitor (FC) [9] are termed as classical inverter due to.an extensive application in research and industries. A single cell of Hbridge inverter have a DC source with four switches, combination of such cell can produce any output voltage level by cascading the cells. Of H bridge inverter is popular for multilevel application with
modulation techniques such as sinusoidal pulse width modulation (SPWM) [1012], selective harmonic elimination [1314], hybrid modulation methods [1516] nearest level technique [17] have been proposed and analyzed depending of inverter configurations. Among the numerous pulse width modulation (PWM) techniques sinusoidal pulse width modulation and space vector pulse width modulation are most widely used modulation techniques. Space vector PWM [11, 18] enables the efficient use of DC voltages that smartly works with vector control hence contributes less THD, better power factor and less switching losses at higher frequencies.
In this paper, analysis of three phase Ttype inverter [19] configuration is done using a modified SVPWM as control strategy for providing switching pulses.


THREE LEVEL TTYPE INVERTER Threephase threelevel inverter configuration for
Cascaded Hbridge (CHB), Neutral Point Clamped (NPC)
and Flying Capacitor is shown in Fig.1. Present work is focused on a threephase Ttype inverter having comparatively reduced number of switches as depicted in Fig.2. Each phase of the threephase Ttype inverter constitutes two IGBT switches and one bidirectional switch. The IGBT switches (Sx1 and Sx2) x= (a, b, c), and the bi directional switch (Sx3) blocks only half of the DClink voltage. Whereas, the neutralpoint clamped (NPC) inverter uses two switches connected in series to block the full DC link voltage. Thus the conduction losses of Ttype inverter are considerably reduced compared to that of NPC inverter.
photovoltaic (PV) as it require isolated sources. Larger number of DC source for higher level is the limitation for H bridge multilevel inverter. An inverter where one DC source with extra diodes connected to the neutral point thus avoiding use of larger number of DC source as earlier and this structure named as neutral point clamped (NPC) inverter. Large number of Diode restricts the application of NPC with increase in
Sa1
VDC
Sa4
Sa3
Sa2
Sb1
VDC
Sb4
Sb3
Sb2
Sc1
VDC
Sc4
Sc3
Sc2
output voltage level. Flying capacitor inverter uses capacitors in place of diodes but the number of capacitors also limits it for higher level application.
Synthesizing a nearly sinusoidal output voltage is accomplished using various switching methods. Numerous

Threelevel Cascaded HBridge
VDC
VDC
2
Da1
D
Sa1
Sa2
Da4
Sa3
Da3
Db1
Sb1
Sb2
Db4
Sb3
Db3
Dc1
Sc1
Sc2
Dc3
Dc4


PRINCIPLE OF OPERATION
Each phase of threelevel Ttype inverter operates in three different modes and generates output voltage in threelevels.
ModeI: In this mode of three level Ttype inverter, switch Sa1 is turned ON and the phase current flows through the switch Sa1 and the output voltage becomes 0.5 VDC.
ModeII: In this mode of threelevel Ttype inverter, switch Sa3 is turned ON and the phase current flows through
VDC
a2 Da5
Db2
Db5
Dc2
Sc3
Dc5
the switch Sa3
and the output voltage becomes 0. In this mode
2
Sa4
Da6
Sb4
Db6
Sc4
Dc6
always two diodes conducts irrespective of the direction of current.
ModeIII: In this mode of threelevel Ttype inverter, switch Sa2 is turned ON and the phase current flows through

Threelevel Neutral point clamped
the switch Sa2 and the output voltage becomes 0.5 VDC.
VDC
VDC
2
VDC
2
Sa1
Sa2
Da4
Sa3
Da5
Sa4
Da3
Sb1
Sb2
Db4
Sb3
Db5
Sb4
Db3
Sc1
Sc2
Sc3 Sc4
Dc3
Dc4
Dc5
Vdc
2
Vdc
2
Da3
Sa3
Da6
Sa1
Da5
Da4
Sa2
Da1
Da2
Da6
Db6
Dc6

ModeI.

Threelevel Flying capacitor

Fig.1 Basic threelevel inverter topology.
Bidirectional switch in Fig.2 has only one IGBT switch and four diodes where two diodes connected in series for forward conduction and two of them used for blocking half of DClink voltage.
TABLE . 1. SWITCHING TABLE FOR PHASEA THREE PHASE TTYPE MLI
Vdc
2
Vdc
2
Da3
Sa3
Da6
Sa1
Da5
Da4
Sa2
Da1
Da2
Sa1
Sa3
Sa2
Output voltage
ON
OFF
OFF
0.5 VDC
OFF
ON
OFF
0
OFF
OFF
ON
– 0.5 VDC
Sa1
Sa3
Sa2
Output voltage
ON
OFF
OFF
0.5 VDC
OFF
ON
OFF
0
OFF
OFF
ON
– 0.5 VDC
2

ModeII.
Sa1
Da1
Threephase Ttype inverter generates three levels of output voltage of magnitude 0.5VDC, 0 and 0.5VDC with proper switching pulse. The switching table for PhaseA of T type inverter is shown in table 1. A delay must be introduced between the switching of switches to avoid the short circuiting of DC source.
Vdc
2
Da3
Sa3
Da6
Da5
Da4
S
Da2
Vdc
2
Sa1
Da3 D
Da1
D
Sb1
D
Db1 D
Sc1
D
Dc1

a2

a5
Sa3
b3 b5
Sb3
c3 c5
Sc3



ModeIII.
Fig.3. Modes of operations
Keeping in mind the cost and efficiency of the overall
Vdc
2
Da6
Da4
Sa2
Db6
Da2
Db4
Sb2
Dc6
Db2
Dc4 Sc2
Dc2
given systems, our keen interest in the reliability is increasing. Thus most of the modern research works are conducted keeping in mind the reliability of efficient power conversions particularly in the area of fault diagnosis and
Fig.2. Threelevel Ttype Inverter configuration.
fault tolerant control strategy.


CONTROL STRATEGY
The Space Vector Pulse Width Modulation (SVPWM)
The modulation index (Mi) depends on the magnitude of reference voltage Vref. The ideal relationship between modulation index Mi and Vref is defined as:
schemes are developed to find the three nearest nodes on the
voltage hexagon lattice with respect to the reference vector. The mathematical formulation of the early SVPWM were
M 0.907Vref
i 0.866VDC
(5)
complex, because the voltage hexagon lattice was used in the Cartesian coordinate system. The coordinates of the nodes on the lattice are fractional numbers, which made the node selection difficult. The idea was that the reference vector was transformed from the Cartesian coordinate system to the 60 degree coordinate system. The 60 degree coordinate system represents one sector on the lattice and its benefit is that the coordinates for the nodes can be represented as integers. Therefore determination of the nodes could be accomplished by simple rounding functions and integer calculation.
In linear modulation region (0 Mi .907):
Here a modified SVPWM technique is introduced for the threephase threelevel inverter. For a particular reference vector, the sector of operation (Pi) and the angle ( ) is
determined by using equations (1) and (2), respectively.
The location of reference vector in any particular triangle
( i) can be determined with the decomposition vector (Vr, Vr) of reference vector. According to NEAREST THREE VECTOR(NTV) method, every vertex of a triangle is considered as a switching vector and every switching vector is represented by many switching states for selected location in a particular triangle. For a threelevel inverter there are 27 switching states (n3 states for an nlevel inverter). The space vector pulse width modulation is determined by selecting and analyzing every switching state for the given triangle of their respective ontimes. Every switching state is responsible for the significant performance of the inverter.
The ontime is defined as Ts=Ta+Tb+Tc. The voltsec equation time averaging is followed:
VrefTs=VaTa+VbTb+VcTc (6)
60
60
Pi int 1
60
60
rem
(1)
(2)
n axis
[11 1]Where, is denoted as the angle of reference vector with respect to axis,int and rem indictes the function for integer and remainder respectively. The SVPWM diagram is divided into six sectors and each sector has four triangle depicted in Fig.4 with corresponding switching states.
4
[00 1] [110] [10 1]2 Vref
1
[111] [0 11]axis
[111] [1 1 1] [000] [111]3
0 1 1
100
m axi
[1 1 1] [110] [111] [010] [110][111] [10 1]
Vref
Where, V
ref
Fig.5. Triangles in sector one.
is the reference voltage and Ts
is the PWM
[111] [111] [011] [111] [111] [000] [100] [0 11]axis
[111]time. Here, two active vectors (Va, Vb) and zero vector is used as Vc.
For a threelevel inverter time T , T , T are defined as:
[10 1] [111] [001] [101] [111] [110]Ta Ts 1 2Mi sin
a b c
T T 2M sin
Linear Mode
b s i 1
[111] [0 11] [111]3
(7)
Fig. 4 Space vector diagram of a three level inverter.
T T 2M sin
c s 1 i 3
The reference voltage vector with magnitude Vref moves on a circular trajectory. The modulation index Mi can be controlled as the trajectory is laying inside the hexagon. The decomposition vector (Vr, Vr) of the reference voltage into – axis having 600 angle to each other, for an Nlevel inverter can be determined as
2N 1Vref

SWITCHING PATTERN GENERATIONS
A variable switchingpattern has been developed for better harmonics. The sevensegment switching patterns can be applied for triangle (or space vectors) having less number of switching redundancy and ninesegment for higher number
Vr
3Vdc
2 N 1V
sin
(3)
of switching redundancy. Depending on the redundancies of the switching states at the vertices of the triangles seven
Vr
3Vdc
ref sin
3
(4)
segment and nine segment time division is distributed for the threelevel inverter as shown in Fig. 67.
SECTOR 1 4 :
200
[00 1] [10 1] [110] [10 1] [00 1] Ta
Ta
Tb
Tc
Tb
Ta
[00 1] [10 1] [110] [10 1] [00 1] Ta
Ta
Tb
Tc
Tb
Ta
[11 1]
Va Vb
[11 1]0
200
Vab (V)
Vab (V)
0 0.02 0.04 0.05
Mag (% of Fund.)
Mag (% of Fund.)
Time (s)
Vc
Tc
4 2 2 2 2 2 4
Ts
Fig. 6 seven segment switchingdiagram.
Ninesegment switching pattern implementation is preferred to the sevensegment switching sequence, where redundancies of switching states are increased for triangle say
1 and 2 . The switching pattern for the sevensegment and the ninesegment is shown in table II.
SECTOR 1 2 :
[0 1 1][00 1] [10 1] [100] [110] [100] [10 1] [00 1][0 1 1]Fundamental (50Hz) = 179.8 , THD= 21.36%
10
5
0
0 2000 4000 6000
Frequency (Hz)

Output voltage waveform and THD of Ttype inverter with modlation index (Mi) =0.907 for seven segment implementation.
Vab (V)
Vab (V)
200
0
200
0 0.02Time (s) 0.04 0.05
Mag (% of Fund.)
Mag (% of Fund.)
Fundamental (50Hz) = 173.9 , THD= 30.30%
Va
Vb Vc
T T T T T
T T T T
10
5
0
0 2000 4000 6000
Frequency (Hz)
a c b a c
a b c a

Output voltage waveform and THD of NPC inverter with
6 3 2 3 3 3 2 3 6
Ts
Fig.7. Ninesegment switchingdiagram.
TABLE II. SWITCHING SEQUENCE PATTERN OF FOUR TRIANGLES IN SECTOR ONE
modulation index (Mi) =0.907 for seven segment implementation.
Vab (V)
Vab (V)
100
Seven Segmentation
Nine Segmentation
3 : 0 11 111
10 1 100 10 1
111 0 11
1 : 1 1 1 0 1 1
00 1 000 100
000 00 1 0 1 1
1 1 1
4 : 00 1 10 1
111 110 111
10 1 00 1
2 : 0 1 1 00 1
10 1 100 110 100
10 1 00 1 0 1 1
Seven Segmentation
Nine Segmentation
3 : 0 11 111
10 1 100 10 1
111 0 11
1 : 1 1 1 0 1 1
00 1 000 100
000 00 1 0 1 1
1 1 1
4 : 00 1 10 1
111 110 111
10 1 00 1
2 : 0 1 1 00 1
10 1 100 110 100
10 1 00 1 0 1 1
0
100
0 0.01 0.02 0.03 0.04 0.05
Mag (% of Fund.)
Mag (% of Fund.)
Time (s)
Fund. (50Hz) = 81.63 , THD= 55.01%
20
10
0
0 2000 4000 6000
Frequency (Hz)


SIMULATION RESULTS
Modified threelevel space vector pulse width modulation technique is applied on Ttype inverter and NPC and corresponding output voltage with total harmonic distortion is depicted in Fig. 5. It is observed that Ttype inverter have relatively reduced THD than NPC. The benefit for Ttype inverter is the requirement of number of switches which reduces the cost of the inverter and complexity of circuit. Table.3. represents the comparison of Ttype with classical configuration for component count.

Output voltage waveform and THD of Ttype inverter with modulation index (Mi)=0.454 for nine segment
implementation.
Vab (V)
Vab (V)
100
0
100
0 0.01 0.02 0.03 0.04 0.05
Time (s)

L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, M. A. M. Prats, The age of multilevel converters arrives, IEEE Ind. Electron. Mag., vol. 2, pp. 2839, 2008.

J. Wen, K. Ma. Smedley, Synthesis of multilevel converters based on single and/or threephase converter building blocks, IEEE Trans. Power Electron., vol. 23, pp. 12471256, 2008.

B. Mahato, P.R. Thakura, and K.C. Jana, "Hardware Design and
Mag (% of Fund.)
Mag (% of Fund.)
Fundamental (50Hz) = 79.49 , THD= 50.13%
20
10
0
0 2000 4000 6000
Frequency (Hz)


Output voltage waveform and THD of NPC inverter with modulation index (Mi)=0.454 for nine segment
implementation.
Fig.8. Output voltage waveform and THD for different modulation index (Mi).
TABLE 3. COMPARISON OF THREEPHASE MLIS WITH TTYPE MLI.
Inverter Type/ Number of Component
CHB MLI
(Symm.)
NPC MLI
FC MLI
TType MLI
IGBTS
/MOSFETS
12
12
12
6
Bidirectional controlled switches
0
0
0
3
Diodes
12
18
12
18
Separate Supply/DC link Capacitor
3
2
2
2
Flying Capacitor
0
0
3
0


CONCLUSION
The selection of Ttype inverter is made based on the benefits of reduced component count in the multilevel than the classical multilevel inverters. A modified space vector pulse width modulation is modelled that proposed variable switching patterns by using sevensegment for space vectors having less number of switching redundancy and nine segment for higher number of switching redundancy to reduce harmonics. The whole circuit is simulated using MATLAB/SIMULINK platform. The simulation results of line voltages of two different multilevel inverters are presented. It is observed that, for a Ttype inverter, there is a significantly improved harmonic profile than the neutral point clamped inverter for the same voltage level.
REFERENCES

R. H.BAKER, L. H.BANNISTER, 1975. Electric Power Converter, U.S. Patent 3 867 643.

S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo,
B. W. Bin Wu, J. Rodriguez, M. a. Perez, and J. I. Leon, Recent Advances and Industrial Applications of Multilevel Converters, IEEE Trans. Ind. Electron., vol. 57, no. 8, pp. 25532580, 2010.

Cheng, Y., Qian, C., Crow, M. L., Pekarek, S., Atcitty, S.: A comparison of diodeclamped and cascaded multilevel converters for a STATCOM with energy storage, IEEE Trans. Ind. Electron., vol. 53, pp. 15121521, 2006.

M. Malinowski, K. Gopakumar, , J. Rodriguez, , and M. A. Pe. Andrez, A Survey on Cascaded Multilevel Inverters, IEEE Trans. Ind. Electron., vol. 57, pp. 21972206, 2010.
Implementation of Unity Power Factor Rectifiers Using Microcontrollers," in Power Electronics (IICPE), 2014 IEEE 6th India International Conference on , vol., no., pp.15, 810 Dec. 2014.

A. Nabae, I. Takahashi, and H. Akagi, A New NeutralPointClamped PWM Inverter, IEEE Trans. Ind. Appl., vol. IA17, no. 5, pp. 518 523, 1981.

T. A. Meynard and H. Foch, MultiLevel Conversion: High Voltage Choppers and VoltageSource Inverters, in PESC `92 Record. 23rd Annual IEEE Power Electronics Specialists Conference, 1992, pp. 397403.

K. C. Jana, S. K. Chowdhury, and S. K. Biswas, Performance evaluation of a simple and general space vector pulsewidth modulationbased Mlevel inverter including overmodulation operation, IET Power Electron., vol. 6, no. 4, pp. 809817, 2013.

K. C. Jana and S. K. Biswas, Generalised switching scheme for a space vector pulsewidth modulationbased Nlevel inverter with reduced switching frequency and harmonics, IET Power Electron., pp. 19, 2015.

K. Gupta and A. M. Khambadkone, A general space vector PWM algorithm for multilevel inverters, including operation in overmodulation range, IEEE Trans. Power Electron., vol. 22, no. 2, pp. 517526, 2007.

H. Lou, C. Mao, D. Wang, J. Lu, and L. Wang, Fundamental modulation strategy with selective harmonic elimination for multilevel inverters, IET Power Electron., vol. 7, no. 8, pp. 21732181, 2014.

G. Hosseini Aghdam, Optimised active harmonic elimination technique for threelevel Ttype inverters, IET Power Electron., vol. 6, no. 3, pp. 425433, 2013.

K. Ding, Z. Yunping, W. Zhan, W. Zhichao, and Z. Yun, Novel hybrid diodeclamp cascade multilevel converter for high power application, Proc. Chinese Society of Electricl Engineering, 2004, vol. 24, pp. 6267.

C. Rech, and J.R. Pinheiro, Impact of hybrid multilevel modulation strategies on input and output harmonic performances, IEEE Trans. Power Electron., 2007, 22, pp. 967977.

S. Kouro, R. Bernal, H. Miranda, C. a Silva, and J. RodrÃguez, High performance torque and flux control for multilevel inverter fed induction motors, IEEE Trans. Power Electr., vol. 22 (6), pp. 2116 2123, 2007.

S. Vasudevamurthy and Swetha, Simulation And Comparison Of Space Vector Pulse Width Modulation For Three Phase Voltage Source Inverter, Int. J. Eng. Res. Technol.,vol. 2, no. 5, pp. 16911698, 2013.

U. Choi, K. Lee, and F. Blaabjerg, Diagnosis and Tolerant Strategy of an OpenSwitch Fault for TType ThreeLevel Inverter Systems, IEEE Trans. Ind. Appl., vol. 50, no. 1, pp. 495508, 2014.