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International Journal of Power Electronics and Drive System (IJPEDS)
Vol. 6, No. 4, December 2015, pp. 906~918
ISSN: 2088-8694  906
Journal homepage: http://iaesjournal.com/online/index.php/IJPEDS
Implementation of Space Vector Modulator for Cascaded
H-Bridge Multilevel Inverters
Syamim Sanusi, Auzani Jidin, Tole Sutikno, Kasrul Abdul Karim, Mohd Luqman Mohd Jamil,
Siti Azura Ahmad Tarusan
Faculty of Electrical Engineering, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka
Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia
Article Info ABSTRACT
Article history:
Received Jul 26, 2015
Revised Oct 30, 2015
Accepted Nov 16, 2015
The Space Vector Modulation (SVM) technique has gained wide acceptance
for many AC drive applications, due to a higher DC bus voltage utilization
(higher output voltage when compared with the SPWM), lower harmonic
distortions and easy digital realization. In recent years, the SVM technique
was extensively adopted in multilevel inverters since it offers greater
numbers of switching vectors for obtaining further improvements of AC
drive performances. However, the use of multilevel inverters associated with
SVM increases the complexity of control algorithm (or computational
burden), in obtaining proper switching sequences and vectors. The
complexity of SVM computation causes a microcontroller or digital signal
processor (DSP) to execute the computation at a larger sampling time. This
consequently may produce errors in computation and hence degrades the
control performances of AC motor drives. This paper presents a
developement of SVM modulator for three-level Cascaded H-Bridge
Multilevel Inverter (CHMI) using a hybrid controller approach, i.e. with
combination between the DS1104 Controller Board and FPGA. In such way,
the computational burden can be minimized as the SVM tasks are distributed
into two parts, in which every part is executed by a single controller. This
allows the generation of switching gates performed by FPGA at the
minimum sampling time 540 to obtain precise desired output
voltages, as can be verified via simulation and experimental results.
Keyword:
Cascaded h-bridge
CHMI
Multilevel inverter
Space vector modulation
Three levels inverter
Copyright © 2015 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Syamim Sanusi
Faculty of Electrical Engineering
Universiti Teknikal Malaysia Melaka
Hang Tuah Jaya, 76100 Durian Tunggal
Melaka, Malaysia
Email: syamisanusi@student.utem.edu.my
1. INTRODUCTION
The Space Vector PWM (or known as SVM) is one of the most popular PWM techniques because of
a higher output voltage and flexible to be implemented in advanced vector control of AC motors [1-3].
Technically, it was reported that the SVM is the most favorable modulation technique among PWM scheme
due to several advantages, higher output voltage, reducing harmonic ripple and able to optimized the
switching sequence [4]. Besides that, this modulation scheme also offer in optimizing the used of dc voltage
link utilization which means it can increase the ration of output magnitude voltage.
In general, the implementation of SVM involve with the used of DSP board and required sector
identification which brings into the formations of rotating space vector diagram. [5]. In the three phase
system, there are six fractions in the space vector diagram spinning 360° which each has equally divided by
60°. This space vector diagram is a transformation from a balance of three phase quantities into two phase
IJPEDS ISSN: 2088-8694 
Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi)
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system of α-β reference frame [4]. The SVM main operation is to used the nearest three vector recognition of
the reference voltage and determined the corresponding on-time using the principles of volt second
equivalent [6]
A multilevel inverter offers greater number of voltage vectors as compared to eight vectors for a
two-level inverter. Figure 1 illustrates the space vector diagrams for Sector I, in a two-level inverter and
three-level inverter. The space vector diagrams can be used to compare the implementation of SVM in two-
level and three-level inverters. As compared to two-level space vector diagram, the sector in three-level
inverter is divided into four identical smaller triangles (i.e. ∆ , ∆ , ∆ and ∆ ). To reduce THD (or ⁄ )
and switching losses in multilevel inverter (i.e. three-level), it is necessary to switching vectors which are the
nearest to the reference vector ̅∗
. Hence, three-level SVM switch the vectors ̅ , ̅ and ̅ for a given
reference vector.
The calculation of on-duration in multilevel SVM is quite complicated and different for various
triangles due to small triangles in the space vector diagram of three-level inverter in Fig.1 do not exactly
imitate the geometry of a sector of two-level inverter. In two-level SVM, the calculation of on-duration is
straightforward which is valid for every sector. However, the three-level SVM needs to modify the reference
vector with new origin point to apply the two-level based SVM for calculating on-duration. As shown by
Figure 1 (b), the modified reference vector ̅∗
with vector ̅ as origin point is determined such that the
calculation of on-duration is similar to that of two-level based SVM. The calculation becomes complicated if
the reference voltage vector ̅∗
lies in triangle	∆ , where the orientation of triangle is different among others;
as can be seen the triangles ∆ , ∆ and ∆ have the same orientation with a single triangle or Sector I in two-
level SVM, as shown in Fig.1. The complexity increases as number of level of inverter becomes higher, e.g.
in five-level inverter, there are six triangles among sixteen triangles, that have different orientation.
The implementation of SVM for multilevel inverters require some important parts which are as
follows; (1) detection of sector , (2) detection of triangle ∆ , (3) calculation of on-duration for switching the
nearest vectors, and (4) determination the switching sequence for every switching period.
As found in literature, there are two common methods to calculate the on-durations. The first method
is to detect the triangle and solve three simultaneous equations of the triangle to determine the on-times as
suggested in [7]. The second method is to detect the triangle and use particular on-duration equations stored
in a lookup table for this triangle, as proposed in [8]. Both of these methods however require complex
computations as the number of level increases.
Alternatively, the calculation of on-duration can be obtained using general algorithms [9] and [10].
Specifically, [9] uses a Euclidean vector system with several matrix transformation, provided that it does not
provide a systematic approach for real time SVM implementation. On the other way, [10] calculated on-
duration and obtained switching states by means of coordinate system, where the axes are 60 degrees apart.
However, the 60 degrees transformation leads to the complexity since the voltage reference is commonly
defined in the orthogonal coordinate system.
Recently, a simple SVM algorithm for multilevel inverters based on standard two-level SVM was
proposed in [11]. The two-level based SVM concept is initiated by [12-14], however, the calculation of on-
duration is based on origin modification and 60 degrees coordinate transformation, which cannot be extended
in implementing SVM for higher levels, i.e. greater than three. Unlike the former methods, the
Figure 1. Comparison Between (a) Two-Level Space Vector Diagram and (b) Three-Level Space Vector
Diagram, e.g. for Sector I.
(a) (b)
̅∗
̅∗
̅
̅
̅
̅
̅
̅
̅
̅
̅
∆
∆
∆
∆
̅∗
Sector I
Sector I
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implementation of SVM proposed in [11] that includes the detection of sector and triangle, and calculation of
on-duration were derived geometrically and systematically which suitable for any level of inverter.
.
2. TOPOLOGY OF THREE-LEVEL CASCADED H-BRIDGE MULTILEVEL INVERTER
The smallest number of level for Cascaded H-bridge Multilevel Inverter (CHMI) is three levels.
Figure 2 shows a topology circuit of 3-level CHMI, which consists of three full bridge inverters (or known as
H-bridge). Each bridge consists of two legs, 4 power switches, i.e. IGBTs and an identical isolated DC
voltage. The isolated DC voltage for three-level CHMI is designated as . The first leg of each bridge is
connected to its phase or winding of a three-phase induction motor, while another leg is shorten as a common
point which referred to as a neutral point, . In any H-bridge inverter, it can produce three states of output
voltage, i.e. , 0	or - , as given in (1).
. (1)
Where and are the respective switching states for the upper switches of the first and second legs of
the -phase H-bridge inverter. Note that the switching of upper and lower switches in the same leg must be
complimentary to each other to avoid short circuit conditions.
3. SPACE VECTOR MODULATION
3.1. Mapping Vector
Compare with the two-level inverter basic concept, the three-phase quantities of stator voltage vector
can be expressed into a space voltage vector form by substituting the basic algotithm of two levels phase
stator voltages with equation (1), the space voltage vector can also be written in terms of switching states and
DC link voltage. Then it can be express into - and -axis components of stator voltage, as follows:
3
2 (2)
1
√3 (3)
Fig. 3 shows voltage vectors available in the three-level CHMI. All voltage vectors are mapped on
the - and -axis plane by applying every switching state possibility in (2) and (3). From this figure, the
mapping of voltage vectors forms six sectors, where each sector contains four small of triangulars and the
voltage vectors can be categorized into four groups as follows: 1) long amplitude of voltage vectors, i.e. ̅ ,
̅ ,…, ̅ , 2) medium amplitude of voltage vectors, i.e. ̅ , ̅ ,…, ̅ , 3) short amplitude of voltage vectors
i.e. ̅ , ̅ ,…, ̅ , and 4) zero voltage vector, i.e. ̅ . It should be noted that each long or medium voltage
Figure 2. Topology Circuit of Three-Level Cascaded H-Bridge Multilevel Inverter
N
	
Induction
Machine
IJPEDS ISSN: 2088-8694 
Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi)
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vector has only a single of switching states, however, the number of switching states increases as the
amplitude of vector reduces toward the origin of the plane.
3.2. Determination of Sector and Triangle
From Figure 3, it can be noticed that the mapping of active vectors forms a hexagonal boundary, in
which the hexagonal can be equally divided into six sectors. This means the difference between the two
angles of adjacent active voltage vectors is 600
. It should be noted that the space voltage vector can also be
expressed into a polar form, as below:
̅∗ ∗
∠ (4)
Taking into account that the unit of is expressed in radian which varies between 0 and 	 rad.
The involvement of negative value in variation complicates the calculation. Therefore, a small
modification is made using a modulus technique, such that the equivalent variation obtained between 0° and
360°. The following equations need the transformation of in degrees and the modulus operation to have
the positive value variations, i.e. . The six sectors can be easily determined by substituting the positive
variations into (5), this yields:
60
	1
(5)
With the increasement number of level, the termination of sector for multilevel need to deals with
the existence of small segment of triangles (i.e. ∆ , where =0, 1, 2 or 3) inside each sector for calculating on-
duration of voltage vectors wihich its similar to the two-level based SVM [11]. In such way, the definition of
reference voltage vector is based at which triangle the vector is located, where the calculation of on-duration
of voltage vectors in a triangle is treated the same way as the vectors in a sector for two-level based SVM. To
obtain	∆ , at first, the angle within a sector needs to be obtained using (6).
Figure 3. Voltage Vectors in the Three-Level CHMI Obtained in Equantions (2) and (3) for Every Switching
State Possibility (Sa1Sa2Sb1Sb2Sc1Sc2)
(100110)
̅
(101001)(011001)
(011000)
(011010)
(010010)
(010110)
(100100)
(100101)
(100001)(101000)
(000001)
(100000)
(000101)
(000100)
(100010)
(000010)
(010100)
(010000)
(001010)
(001000)
(010001)
(101010)
(010101)
̅̅ 	
̅
̅ 		
̅ 		
̅
̅
(001001)
̅ 		
̅ 		 ̅̅
̅
̅
̅ 		
̅
̅
(000000)
(000110)
̅
√
Sec I
Sec II
Sec III
Sec VI
Sec V
Sec IV
̅
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, 60 (6)
Then, let the identification of triangle is made by considering the sector at which the reference
voltage vector is located. Based on the - and -axis plane, the components of reference voltage vector can
be written as:
∗
	 ∗
cos	 (7)
∗
	 ∗
sin	 (8)
Alternatively, the equivalent voltage vector ̅∗
based on - and -axis plane in a triangle is defined (as
illustrated in zoomed images in Figure 4(b) and (c)), hence the components of the vector can be calculated as:
̅∗
	 ∗ ∗
(9)
From the vector diagrams shown in Figure 4, it can be noticed that the definition of reference
voltage vector within a small triangle for triangle ∆ , ∆ and ∆ is similar to that defined in Sector I for the
case of two-level based SVM. Geometrically, the triangle ∆ (for =0, 1 or 3) and the vector components ∗
and ∗
can be calculated using the following equations [11]:
∗ ∗
2
2
3
(10)
∗ ∗
√3
(11)
∆ 2 (12)
where and are obtained using (13) and (14):
3
2
∗
∗
√3
(13)
√3
∗
(14)
On the other hand, the definition of reference voltage vector within a small triangle for triangle∆ is
similar to that defined in Sector IV for the case of two-level based SVM. It can be proved geometrically that
the triangle ∆ and the vector components ∗
and ∗
can be computed using (15), (16) and (17),
respectively [11].
∗
3
1 2 ∗ (15)
∗
√3
1 ∗
(16)
∆ 2 1 (17)
In Fig.4(a), k1 equation is represented by the vertical line which inclines at 120° to α axis. The result
of this equation will only produce two states, either k1= 0 or k1= 1. If k1=0, the reference vector is in the
region of ∆1. Indicate a blue colored parallel line between upper and below triangle to separated ∆3 from the
rest. This line is referrer as k2 has a distance value of 2 √3⁄ from α plane. Refer to previous Figure 2, the
value of 2 √3⁄ is a height of every small triangle from the based to the tips of triangle. To identify which
equations should be used in determining the triangle and vector components, it is necessary to evaluate the
condition below [11]:
∗
√3 ∗
(18)
where ∗
and ∗
are obtained using (19) and (20).
IJPEDS ISSN: 2088-8694 
Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi)
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∗
3
2
∗ √3
2
(19)
∗
√3
3 ∗
2 2
(20)
From (18), if the condition is satisfied, hence the triangle ∆ (for =0, 1 or 3) and the vector components ∗
and ∗
can be calculated using (10), (11) and (12). But, if the condition is not satisfied, the triangle ∆ and
the vector components ∗
and ∗
can be obtained using (15), (16) and (17).
3.3. Calculation of On-Duration for Switching Vectors
The general representation of vector diagrams as shown in Figure 4 (b) and Figure 4 (c) is necessary
for calculating the on-duration of application for each vector, ̅ , ̅ and ̅ . In general, the calculation of
on-duration can be obtained by considering the vector diagram ia applicable for any triangle in any sector.
The on durations for switching two adjacent voltage vectors of ̅∗
are calculated by the following equations
[11]:
	
3
2
∗
	
1
√3
∗
(21)
	
√3	 ∗
∙
(22)
(b)
Zoomed
image
̅∗
∗
∗
(c)
Zoomed
image
Figure 4. Definition of Reference Voltage Vector of Triangle
(∆ and ∆ )
̅∗
∗
∗
̅∗
∗ ∗
̅∗
̅∗
∗ ∗
̅
̅
̅
̅∗
∗ ∗
∗ ∗
̅
̅
̅
β
Sector 1
αr
Δ
2
Δ
1
Δ
0
Δ
3(a)
k2
k1
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It should be noted that the switching period, is the total summation of on-durations for applying two
adjacent voltage vectors and a vector which is defined as origin point to state the ̅∗
, i.e; ̅ , ̅ and ̅ .
Hence, the on-duration for applying the vector (as the origin point, as shown in Figure 4) can be simply
obtained as:
	 (23)
3.4. Calculation of Duty Ratios
Major consideration in generating proper switching states (or PWM signals) is to provide high
degrees of accuracy and linearity to obtain desired output voltages. At this stage, appropriate pulse width of
pre-switching states ( , ,	and for each phase are generated based on the comparison between their
respective duty ratio and the triangular waveform, as illustrated in Figure 4. Note that the pre-switching states
are defined to determine the on-durations of voltage vectors which are valid for every sector as well as
triangle.
Based on the definition of on-duration marked in Figure 5, the duty ratios, i.e. , and for each
phase in terms of on-durations in the case of three-level CHMI can be calculated using the following
equations:
	
2
4 (24)
	
2
4 2 (25)
	
2
4 2 2 (26)
3.5. Generation of Switching States
The switching operations of twelve IGBTs in the three-level CHMI are driven by the switching
status, , , , , and (and also their respective complimented status ̅ , ̅ , ̅ , ̅ , ̅ and
̅ ) which are generated from a look-up table. The look-up table requires information of number of sector,
triangle and pre-switching states. The switching status in the look-up table is mapped such that the switching
vector for every sector as well as triangle satisfies the criteria and the switching sequence. It should be taking
into account that the information of pre-switching states ( , ,	and ) will determine six switching states
to drive upper switching devices for each leg of three H-bridge inverters (while the lower switching devices
are driven by the complimented states).
Figure 5. Generation of Pre-Switching States
4
										
2 2 4
1
0
1
0
0
0
1
1
4 2 2
			
4
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4. DESCRIPTION OF EXPERIMENTAL SETUP
This section describes the tasks of circuits or components employed to set up the experimental
platform for verifying the effectiveness of SVM control algorithm for three-level inverters. From Figure 6, it
can be noticed that two controller boards are utilized to perform the tasks of SVM control algorithm. The
reason of using two controller boards is that to minimize the computational burden of the main controller
board which is DS1104 R&D Controller Board.
In implementing the SVM, its tasks are distributed into two parts, in which each part is performed by
a single controller board. In doing so, the burden of calculation can be minimized; this in turn allows the
computation in the main controller board performed at high sampling frequency.
4.1. DS1104 R&D Controller Board
The DS1104 R&D Controller Board is known as the most powerful controller board which is widely
used in industry and university for developing system and rapid control prototyping. The major tasks of SVM
algorithm are executed using the DS1104, which include:
 Determination of sector , triangle ∆ , vector components within a sector or triangle ∗
and ∗
.
 Calculation of on-duration and
 Calculation of duty ratios , and
All tasks listed above are implemented using MATLAB-Simulink block diagram with special Real-
Time Interface (RTI) Input/Output blocks. From Fig.6, the DS1104 R&D Controller Board provides
information of sector	 (3-bit), triangle ∆ (4-bit) and pre-switching states , and in digital output
form. In this case the decimal numbers of information are converted into Gray Code to prevent spurious
output by allowing only one bit of binary digit changes for two successive values.
Figure 6. Experimental Setup
DS1104 R&D
Controller Board
ALTERA Cyclone III FPGA
DEO Board
Gate Driver Circuits
Inverter
Three-Phase
Resistive-Inductive load
∆
Isolated DC
Supplies
4-bit 3-bit 1-bit 1-bit 1-bit
̅ ̅ ̅ ̅
̅ ̅ ̅ ̅
ControlDesk
Graphical Programming
Approach
Observation/analysis
via Oscilloscope
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4.2. Altera FPGA DEO Controller Board
The Altera Field Programmable Gate Arrays (FPGA) DEO Controller Board is known to have high-
speed clock which is superior to execute logical or digital operation. From Figure 6, it can be seen that the
FPGA receives information of sector (3-bit), triangle ∆ (4-bit) and pre-switching states , and in
digital Gray code. The FPGA is responsible to perform the task of selection of appropriate switching states
based on the information received.
In practice, it is compulsory to provide blanking time for upper and lower IGBTs switching
operation to avoid short circuit conditions. The blanking time is set approximately at 2	 by selecting
appropriate threshold value to be compared with counters, implemented in FPGA. For convenience, the
operation of blanking time generation for one leg of any or -phase is described, with the aid of the block
diagram and timing diagram, as illustrated in Figs. 7 and 8, respectively.
From Figure 7, it can be noticed that the signal is the switching state for -phase which is
obtained from the voltage vectors selection table, as mentioned above. The block of MOD18 is assigned to
divide the general clock frequency of FPGA 33.33 by 18, hence the new clock frequency becomes 1.85
(or the new period 540 ). The new clock frequency signal is designated as as shown in Figure 7.
The new clock frequency signal is used to count up the upper counter (or the lower counter) by 1 for every
540 when is active high (or active low), otherwise both counters will be reset to zero. Note the outputs
of upper and lower counter are designated by the respective signals and . By comparing signals a and d
with a constant value of 4, the blanking time is approximated to 2 . Increasing or decreasing the constant
value of 4 will enlarge or reduce the blanking time, respectively. Note that, the signals and ̅ are for the
upper and lower IGBTs of a leg of -phase of VSI. The blanking time generator is duplicated for the other
phases and legs to perform the same effect. Then the outputs of switching states from the blanking time
generator are then fed to the gate driver circuits.
540ns
h
a 4
d
				
				 ̅
4
Figure 8. Timing Diagram of Blanking Time Generation for -Phase and Any Leg
Clk
MOD
18
Upper
Counter
Clk
Clear1
Lower
Counter
Clear1
Comparator
ClkClock
h
a
16-bit
d
16-bit
Cout1
Cout4
Clkout
uc1
lc1
Cin1
Cin4 ̅
4Cinif
4Cinif
0
1
Cout






Figure 7. Block Diagram of Blanking Time Generation for -Phase and Any Leg
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4.3. Power Inverter and Gate Driver Circuits
Figure 9 depicts a gate driver and power inverter circuits which are used to produce desired output
voltages. The purposes of using gate driver circuits are to provide isolation between the electronic control
circuits and power inverter circuits and to provide sufficient power amplification for switching IGBTs. It can
be noticed from Figure 9, there are six units of H-Bridge inverter circuits to establish five-level CHMI. Each
H-Bridge inverter circuit is supplied by an isolated DC voltage supply. From this figure, it also shows that the
FPGA controller board and I/O interface DS1104 card.
4.4. Three-Phase and Series Connected Resistive and Inductive Loads
A three-phase and series connected resistive and inductive load is employed for analyzing the
performance of SVM for two-level, three-level and five-level of inverters. The load is represented by a load
reactor model MV 1101 from TERCO, where its specification and rated condition are given in Table 1.
Table 1. Load Reactor Parameters
Parameters Value
Rated Reactive Power 2.5kVAr
Frequancy 50-60Hz
Rated Voltage 380V Y, 220V Y/∆
Rated step regulation 287.81mH , 28.082 Ω
5. RESULT ANALYSIS OF TOTAL HARMONIC DISTORTION (THD) OF OUTPUT VOLTAGE
This section evaluates the total harmonic distortions (THD) of output voltage and the accuracy of
fundamental output voltage of three-level inverters. The evaluation is based on the simulation results (i.e.
the values of THD and fundamental output voltage are obtained using Fast Fourier Transforms (FFT)
analysis), as well as comparison with the experimental results.
The evaluation on THD of output voltage and the accuracy of fundamental output voltage
resulted in every level of inverter is also carried out at different modulation indices, 0.3 and 0.9. The
simulation results obtained from the evaluation are demonstrated in Figs. 10. From these figures, it can be
observed that the experimental results are in close agreements with the simulation results. Specifically, the
patterns of wave shape and frequency spectrum of output voltages in the experimental results are similar to
that obtained in the simulation results.
The similarities between simulation and experimental results, allow the results of THD and
fundamental output voltage obtained via simulation to be assumed similar with that of experimental results
with the error between the simulation and calculated values is insignificant and approximately less than 1 %.
Figure 9. Photograph of FPGA, Gate Driver Circuits and Cascaded H-Bridge Multilevel Inverter (CHMI)
FPGA
Gate
D i
CHMI
I/O Interface
DS1104
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6. CONCLUSION
This paper presented a technique to implementation the space vector modulator scheme for
multilevel inverters. The designs structure is built to minimize the mathematic algorithms in order to ease the
implementation in hardware. The scheme contains simple althorithm to interpret the on duration and duty
ratio which it all based on the two levels SVM. The implementation required less memory and can be
computationally fast. The scheme can perform very well for any reference vector with any modulation index
and can easily be extended to any levels. The simulation result with FFT analysis and experiment result has
verified the proposed SVM development.
ACKNOWLEDGEMENTS
The authors would like thanks the Ministry of Education Malaysia (KPM) and Universiti Teknikal
Malaysia Melaka (UTeM) for providing the research grant FRGS/2013/FKE/TK02/02/1/F00159 for this research.
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(a)
(b)
Figure 10: Simulation and Experimental Results of Phase Voltage and its Frequency Spectrum when
Modulation Index a 0.3 and (b) 0.9
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Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi)
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[7] Ishida, T., et al. A control strategy for a five-level double converter with adjustable DC link voltage. in Industry
Applications Conference, 2002. 37th IAS Annual Meeting. Conference Record of the. 2002.
[8] Mondal, S.K., J.O.P. Pinto, and B.K. Bose, A neural-network-based space-vector PWM controller for a three-level
voltage-fed inverter induction motor drive. Industry Applications, IEEE Transactions on, 2002. 38(3): p. 660-669.
[9] Celanovic, N. and D. Boroyevich, A fast space-vector modulation algorithm for multilevel three-phase converters.
Industry Applications, IEEE Transactions on, 2001. 37(2): p. 637-641.
[10] Sanmin, W., et al. A general space vector PWM control algorithm for multilevel inverters. in Applied Power
Electronics Conference and Exposition, 2003. APEC '03. Eighteenth Annual IEEE. 2003.
[11] Gupta, A.K. and A.M. Khambadkone, A General Space Vector PWM Algorithm for Multilevel Inverters, Including
Operation in Overmodulation Range. Power Electronics, IEEE Transactions on, 2007. 22(2): p. 517-526.
[12] Haoran, Z., et al., Multilevel inverter modulation schemes to eliminate common-mode voltages. Industry
Applications, IEEE Transactions on, 2000. 36(6): p. 1645-1653.
[13] Jae Hyeong, S., C. Chang Ho, and H. Dong-Seok, A new simplified space-vector PWM method for three-level
inverters. Power Electronics, IEEE Transactions on, 2001. 16(4): p. 545-550.
[14] Poh Chiang, L. and D.G. Holmes, Flux modulation for multilevel inverters. Industry Applications, IEEE
Transactions on, 2002. 38(5): p. 1389-1399.
BIOGRAPHIES OF AUTHORS
Syamim Sanusi was born in 1986 in Kuala Kerai, Kelantan, Malaysia. She received B.Eng.
degree (Hons) from the Universiti Teknikal Malaysia Melaka, Malaysia in 2011 and is currently
pursuing the M.Sc degree in the same University. Her area of research interest includes pulse
width modulation, space vector modulation and multilevel inverters.
Auzani Jidin received the B.Eng. degrees, M.Eng.degrees and Ph.D. degree in power
electronics and drives from Universiti Teknologi Malaysia, Johor Bahru, Malaysia, in 2002,
2004 and 2011, respectively. He is currently a Lecturer with the Department of Power
Electronics and Drives, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka,
Durian Tunggal, Malaysia. His research interests include the field of power electronics, motor
drive systems, field-programmable gate array, and DSP applications.
Tole Sutikno is an expert in the field of power electronics, Industrial Electronics & Informatics,
Embedded Systems and Electric Drives. Since 2001 he has been a lecturer in Electrical
Engineering Department, Universitas Ahmad Dahlan (UAD), Indonesia. He is an Associate
Professor at the above University since 2008. He is an Editor-in-Chief of TELKOMNIKA
Indonesian Journal of Electrical Engineering, and also acts as an Editor in some international
journals in electrical and computer engineering, power electronics, motor drive systems and
FPGA applications areas
Kasrul Abdul Karim received the M.Sc. from University of Bradford and Ph.D. degrees from
the University of Nottingham, UK, in 2003 and 2011, respectively. He is currently a Lecturer
with the Department of Power Electronics and Drives, Faculty of Electrical Engineering,
Universiti Teknikal Malaysia Melaka, Durian Tunggal, Malaysia. His research interests include
electrical machine design, power electronics, and electric vehicle.
 ISSN: 2088-8694
IJPEDS Vol. 6, No. 4, December 2015 : 906 – 918
918
Siti Azura Binti Ahmad Tarusan received B.Eng. degree (Hons) from the Universiti Teknologi
Malaysia, Malaysia and M.Sc. in Industrial Electronics & Control Engineering from University
Malaysia, Malaysia. She is currently a Lecturer with the Department of Power Electronics and
Drives, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka, Durian
Tunggal, Malaysia. Her research interests include power electronic & drive, electrical drive,
renewable energy.
Mohd Luqman Mohd Jamil received the M.Sc. from Newcastle university, UK and Ph.D.
degrees from the The University of Sheffield, UK, in 2003 and 2011, respectively. He is
currently a Lecturer with the Department of Power Electronics and Drives, Faculty of Electrical
Engineering, Universiti Teknikal Malaysia Melaka, Durian Tunggal, Malaysia. His research
interests include power electronics, design and analysis of electric machines and also motor
drives

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Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters

  • 1. International Journal of Power Electronics and Drive System (IJPEDS) Vol. 6, No. 4, December 2015, pp. 906~918 ISSN: 2088-8694  906 Journal homepage: http://iaesjournal.com/online/index.php/IJPEDS Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters Syamim Sanusi, Auzani Jidin, Tole Sutikno, Kasrul Abdul Karim, Mohd Luqman Mohd Jamil, Siti Azura Ahmad Tarusan Faculty of Electrical Engineering, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia Article Info ABSTRACT Article history: Received Jul 26, 2015 Revised Oct 30, 2015 Accepted Nov 16, 2015 The Space Vector Modulation (SVM) technique has gained wide acceptance for many AC drive applications, due to a higher DC bus voltage utilization (higher output voltage when compared with the SPWM), lower harmonic distortions and easy digital realization. In recent years, the SVM technique was extensively adopted in multilevel inverters since it offers greater numbers of switching vectors for obtaining further improvements of AC drive performances. However, the use of multilevel inverters associated with SVM increases the complexity of control algorithm (or computational burden), in obtaining proper switching sequences and vectors. The complexity of SVM computation causes a microcontroller or digital signal processor (DSP) to execute the computation at a larger sampling time. This consequently may produce errors in computation and hence degrades the control performances of AC motor drives. This paper presents a developement of SVM modulator for three-level Cascaded H-Bridge Multilevel Inverter (CHMI) using a hybrid controller approach, i.e. with combination between the DS1104 Controller Board and FPGA. In such way, the computational burden can be minimized as the SVM tasks are distributed into two parts, in which every part is executed by a single controller. This allows the generation of switching gates performed by FPGA at the minimum sampling time 540 to obtain precise desired output voltages, as can be verified via simulation and experimental results. Keyword: Cascaded h-bridge CHMI Multilevel inverter Space vector modulation Three levels inverter Copyright © 2015 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Syamim Sanusi Faculty of Electrical Engineering Universiti Teknikal Malaysia Melaka Hang Tuah Jaya, 76100 Durian Tunggal Melaka, Malaysia Email: syamisanusi@student.utem.edu.my 1. INTRODUCTION The Space Vector PWM (or known as SVM) is one of the most popular PWM techniques because of a higher output voltage and flexible to be implemented in advanced vector control of AC motors [1-3]. Technically, it was reported that the SVM is the most favorable modulation technique among PWM scheme due to several advantages, higher output voltage, reducing harmonic ripple and able to optimized the switching sequence [4]. Besides that, this modulation scheme also offer in optimizing the used of dc voltage link utilization which means it can increase the ration of output magnitude voltage. In general, the implementation of SVM involve with the used of DSP board and required sector identification which brings into the formations of rotating space vector diagram. [5]. In the three phase system, there are six fractions in the space vector diagram spinning 360° which each has equally divided by 60°. This space vector diagram is a transformation from a balance of three phase quantities into two phase
  • 2. IJPEDS ISSN: 2088-8694  Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi) 907 system of α-β reference frame [4]. The SVM main operation is to used the nearest three vector recognition of the reference voltage and determined the corresponding on-time using the principles of volt second equivalent [6] A multilevel inverter offers greater number of voltage vectors as compared to eight vectors for a two-level inverter. Figure 1 illustrates the space vector diagrams for Sector I, in a two-level inverter and three-level inverter. The space vector diagrams can be used to compare the implementation of SVM in two- level and three-level inverters. As compared to two-level space vector diagram, the sector in three-level inverter is divided into four identical smaller triangles (i.e. ∆ , ∆ , ∆ and ∆ ). To reduce THD (or ⁄ ) and switching losses in multilevel inverter (i.e. three-level), it is necessary to switching vectors which are the nearest to the reference vector ̅∗ . Hence, three-level SVM switch the vectors ̅ , ̅ and ̅ for a given reference vector. The calculation of on-duration in multilevel SVM is quite complicated and different for various triangles due to small triangles in the space vector diagram of three-level inverter in Fig.1 do not exactly imitate the geometry of a sector of two-level inverter. In two-level SVM, the calculation of on-duration is straightforward which is valid for every sector. However, the three-level SVM needs to modify the reference vector with new origin point to apply the two-level based SVM for calculating on-duration. As shown by Figure 1 (b), the modified reference vector ̅∗ with vector ̅ as origin point is determined such that the calculation of on-duration is similar to that of two-level based SVM. The calculation becomes complicated if the reference voltage vector ̅∗ lies in triangle ∆ , where the orientation of triangle is different among others; as can be seen the triangles ∆ , ∆ and ∆ have the same orientation with a single triangle or Sector I in two- level SVM, as shown in Fig.1. The complexity increases as number of level of inverter becomes higher, e.g. in five-level inverter, there are six triangles among sixteen triangles, that have different orientation. The implementation of SVM for multilevel inverters require some important parts which are as follows; (1) detection of sector , (2) detection of triangle ∆ , (3) calculation of on-duration for switching the nearest vectors, and (4) determination the switching sequence for every switching period. As found in literature, there are two common methods to calculate the on-durations. The first method is to detect the triangle and solve three simultaneous equations of the triangle to determine the on-times as suggested in [7]. The second method is to detect the triangle and use particular on-duration equations stored in a lookup table for this triangle, as proposed in [8]. Both of these methods however require complex computations as the number of level increases. Alternatively, the calculation of on-duration can be obtained using general algorithms [9] and [10]. Specifically, [9] uses a Euclidean vector system with several matrix transformation, provided that it does not provide a systematic approach for real time SVM implementation. On the other way, [10] calculated on- duration and obtained switching states by means of coordinate system, where the axes are 60 degrees apart. However, the 60 degrees transformation leads to the complexity since the voltage reference is commonly defined in the orthogonal coordinate system. Recently, a simple SVM algorithm for multilevel inverters based on standard two-level SVM was proposed in [11]. The two-level based SVM concept is initiated by [12-14], however, the calculation of on- duration is based on origin modification and 60 degrees coordinate transformation, which cannot be extended in implementing SVM for higher levels, i.e. greater than three. Unlike the former methods, the Figure 1. Comparison Between (a) Two-Level Space Vector Diagram and (b) Three-Level Space Vector Diagram, e.g. for Sector I. (a) (b) ̅∗ ̅∗ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ∆ ∆ ∆ ∆ ̅∗ Sector I Sector I
  • 3.  ISSN: 2088-8694 IJPEDS Vol. 6, No. 4, December 2015 : 906 – 918 908 implementation of SVM proposed in [11] that includes the detection of sector and triangle, and calculation of on-duration were derived geometrically and systematically which suitable for any level of inverter. . 2. TOPOLOGY OF THREE-LEVEL CASCADED H-BRIDGE MULTILEVEL INVERTER The smallest number of level for Cascaded H-bridge Multilevel Inverter (CHMI) is three levels. Figure 2 shows a topology circuit of 3-level CHMI, which consists of three full bridge inverters (or known as H-bridge). Each bridge consists of two legs, 4 power switches, i.e. IGBTs and an identical isolated DC voltage. The isolated DC voltage for three-level CHMI is designated as . The first leg of each bridge is connected to its phase or winding of a three-phase induction motor, while another leg is shorten as a common point which referred to as a neutral point, . In any H-bridge inverter, it can produce three states of output voltage, i.e. , 0 or - , as given in (1). . (1) Where and are the respective switching states for the upper switches of the first and second legs of the -phase H-bridge inverter. Note that the switching of upper and lower switches in the same leg must be complimentary to each other to avoid short circuit conditions. 3. SPACE VECTOR MODULATION 3.1. Mapping Vector Compare with the two-level inverter basic concept, the three-phase quantities of stator voltage vector can be expressed into a space voltage vector form by substituting the basic algotithm of two levels phase stator voltages with equation (1), the space voltage vector can also be written in terms of switching states and DC link voltage. Then it can be express into - and -axis components of stator voltage, as follows: 3 2 (2) 1 √3 (3) Fig. 3 shows voltage vectors available in the three-level CHMI. All voltage vectors are mapped on the - and -axis plane by applying every switching state possibility in (2) and (3). From this figure, the mapping of voltage vectors forms six sectors, where each sector contains four small of triangulars and the voltage vectors can be categorized into four groups as follows: 1) long amplitude of voltage vectors, i.e. ̅ , ̅ ,…, ̅ , 2) medium amplitude of voltage vectors, i.e. ̅ , ̅ ,…, ̅ , 3) short amplitude of voltage vectors i.e. ̅ , ̅ ,…, ̅ , and 4) zero voltage vector, i.e. ̅ . It should be noted that each long or medium voltage Figure 2. Topology Circuit of Three-Level Cascaded H-Bridge Multilevel Inverter N Induction Machine
  • 4. IJPEDS ISSN: 2088-8694  Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi) 909 vector has only a single of switching states, however, the number of switching states increases as the amplitude of vector reduces toward the origin of the plane. 3.2. Determination of Sector and Triangle From Figure 3, it can be noticed that the mapping of active vectors forms a hexagonal boundary, in which the hexagonal can be equally divided into six sectors. This means the difference between the two angles of adjacent active voltage vectors is 600 . It should be noted that the space voltage vector can also be expressed into a polar form, as below: ̅∗ ∗ ∠ (4) Taking into account that the unit of is expressed in radian which varies between 0 and rad. The involvement of negative value in variation complicates the calculation. Therefore, a small modification is made using a modulus technique, such that the equivalent variation obtained between 0° and 360°. The following equations need the transformation of in degrees and the modulus operation to have the positive value variations, i.e. . The six sectors can be easily determined by substituting the positive variations into (5), this yields: 60 1 (5) With the increasement number of level, the termination of sector for multilevel need to deals with the existence of small segment of triangles (i.e. ∆ , where =0, 1, 2 or 3) inside each sector for calculating on- duration of voltage vectors wihich its similar to the two-level based SVM [11]. In such way, the definition of reference voltage vector is based at which triangle the vector is located, where the calculation of on-duration of voltage vectors in a triangle is treated the same way as the vectors in a sector for two-level based SVM. To obtain ∆ , at first, the angle within a sector needs to be obtained using (6). Figure 3. Voltage Vectors in the Three-Level CHMI Obtained in Equantions (2) and (3) for Every Switching State Possibility (Sa1Sa2Sb1Sb2Sc1Sc2) (100110) ̅ (101001)(011001) (011000) (011010) (010010) (010110) (100100) (100101) (100001)(101000) (000001) (100000) (000101) (000100) (100010) (000010) (010100) (010000) (001010) (001000) (010001) (101010) (010101) ̅̅ ̅ ̅ ̅ ̅ ̅ (001001) ̅ ̅ ̅̅ ̅ ̅ ̅ ̅ ̅ (000000) (000110) ̅ √ Sec I Sec II Sec III Sec VI Sec V Sec IV ̅
  • 5.  ISSN: 2088-8694 IJPEDS Vol. 6, No. 4, December 2015 : 906 – 918 910 , 60 (6) Then, let the identification of triangle is made by considering the sector at which the reference voltage vector is located. Based on the - and -axis plane, the components of reference voltage vector can be written as: ∗ ∗ cos (7) ∗ ∗ sin (8) Alternatively, the equivalent voltage vector ̅∗ based on - and -axis plane in a triangle is defined (as illustrated in zoomed images in Figure 4(b) and (c)), hence the components of the vector can be calculated as: ̅∗ ∗ ∗ (9) From the vector diagrams shown in Figure 4, it can be noticed that the definition of reference voltage vector within a small triangle for triangle ∆ , ∆ and ∆ is similar to that defined in Sector I for the case of two-level based SVM. Geometrically, the triangle ∆ (for =0, 1 or 3) and the vector components ∗ and ∗ can be calculated using the following equations [11]: ∗ ∗ 2 2 3 (10) ∗ ∗ √3 (11) ∆ 2 (12) where and are obtained using (13) and (14): 3 2 ∗ ∗ √3 (13) √3 ∗ (14) On the other hand, the definition of reference voltage vector within a small triangle for triangle∆ is similar to that defined in Sector IV for the case of two-level based SVM. It can be proved geometrically that the triangle ∆ and the vector components ∗ and ∗ can be computed using (15), (16) and (17), respectively [11]. ∗ 3 1 2 ∗ (15) ∗ √3 1 ∗ (16) ∆ 2 1 (17) In Fig.4(a), k1 equation is represented by the vertical line which inclines at 120° to α axis. The result of this equation will only produce two states, either k1= 0 or k1= 1. If k1=0, the reference vector is in the region of ∆1. Indicate a blue colored parallel line between upper and below triangle to separated ∆3 from the rest. This line is referrer as k2 has a distance value of 2 √3⁄ from α plane. Refer to previous Figure 2, the value of 2 √3⁄ is a height of every small triangle from the based to the tips of triangle. To identify which equations should be used in determining the triangle and vector components, it is necessary to evaluate the condition below [11]: ∗ √3 ∗ (18) where ∗ and ∗ are obtained using (19) and (20).
  • 6. IJPEDS ISSN: 2088-8694  Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi) 911 ∗ 3 2 ∗ √3 2 (19) ∗ √3 3 ∗ 2 2 (20) From (18), if the condition is satisfied, hence the triangle ∆ (for =0, 1 or 3) and the vector components ∗ and ∗ can be calculated using (10), (11) and (12). But, if the condition is not satisfied, the triangle ∆ and the vector components ∗ and ∗ can be obtained using (15), (16) and (17). 3.3. Calculation of On-Duration for Switching Vectors The general representation of vector diagrams as shown in Figure 4 (b) and Figure 4 (c) is necessary for calculating the on-duration of application for each vector, ̅ , ̅ and ̅ . In general, the calculation of on-duration can be obtained by considering the vector diagram ia applicable for any triangle in any sector. The on durations for switching two adjacent voltage vectors of ̅∗ are calculated by the following equations [11]: 3 2 ∗ 1 √3 ∗ (21) √3 ∗ ∙ (22) (b) Zoomed image ̅∗ ∗ ∗ (c) Zoomed image Figure 4. Definition of Reference Voltage Vector of Triangle (∆ and ∆ ) ̅∗ ∗ ∗ ̅∗ ∗ ∗ ̅∗ ̅∗ ∗ ∗ ̅ ̅ ̅ ̅∗ ∗ ∗ ∗ ∗ ̅ ̅ ̅ β Sector 1 αr Δ 2 Δ 1 Δ 0 Δ 3(a) k2 k1
  • 7.  ISSN: 2088-8694 IJPEDS Vol. 6, No. 4, December 2015 : 906 – 918 912 It should be noted that the switching period, is the total summation of on-durations for applying two adjacent voltage vectors and a vector which is defined as origin point to state the ̅∗ , i.e; ̅ , ̅ and ̅ . Hence, the on-duration for applying the vector (as the origin point, as shown in Figure 4) can be simply obtained as: (23) 3.4. Calculation of Duty Ratios Major consideration in generating proper switching states (or PWM signals) is to provide high degrees of accuracy and linearity to obtain desired output voltages. At this stage, appropriate pulse width of pre-switching states ( , , and for each phase are generated based on the comparison between their respective duty ratio and the triangular waveform, as illustrated in Figure 4. Note that the pre-switching states are defined to determine the on-durations of voltage vectors which are valid for every sector as well as triangle. Based on the definition of on-duration marked in Figure 5, the duty ratios, i.e. , and for each phase in terms of on-durations in the case of three-level CHMI can be calculated using the following equations: 2 4 (24) 2 4 2 (25) 2 4 2 2 (26) 3.5. Generation of Switching States The switching operations of twelve IGBTs in the three-level CHMI are driven by the switching status, , , , , and (and also their respective complimented status ̅ , ̅ , ̅ , ̅ , ̅ and ̅ ) which are generated from a look-up table. The look-up table requires information of number of sector, triangle and pre-switching states. The switching status in the look-up table is mapped such that the switching vector for every sector as well as triangle satisfies the criteria and the switching sequence. It should be taking into account that the information of pre-switching states ( , , and ) will determine six switching states to drive upper switching devices for each leg of three H-bridge inverters (while the lower switching devices are driven by the complimented states). Figure 5. Generation of Pre-Switching States 4 2 2 4 1 0 1 0 0 0 1 1 4 2 2 4
  • 8. IJPEDS ISSN: 2088-8694  Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi) 913 4. DESCRIPTION OF EXPERIMENTAL SETUP This section describes the tasks of circuits or components employed to set up the experimental platform for verifying the effectiveness of SVM control algorithm for three-level inverters. From Figure 6, it can be noticed that two controller boards are utilized to perform the tasks of SVM control algorithm. The reason of using two controller boards is that to minimize the computational burden of the main controller board which is DS1104 R&D Controller Board. In implementing the SVM, its tasks are distributed into two parts, in which each part is performed by a single controller board. In doing so, the burden of calculation can be minimized; this in turn allows the computation in the main controller board performed at high sampling frequency. 4.1. DS1104 R&D Controller Board The DS1104 R&D Controller Board is known as the most powerful controller board which is widely used in industry and university for developing system and rapid control prototyping. The major tasks of SVM algorithm are executed using the DS1104, which include:  Determination of sector , triangle ∆ , vector components within a sector or triangle ∗ and ∗ .  Calculation of on-duration and  Calculation of duty ratios , and All tasks listed above are implemented using MATLAB-Simulink block diagram with special Real- Time Interface (RTI) Input/Output blocks. From Fig.6, the DS1104 R&D Controller Board provides information of sector (3-bit), triangle ∆ (4-bit) and pre-switching states , and in digital output form. In this case the decimal numbers of information are converted into Gray Code to prevent spurious output by allowing only one bit of binary digit changes for two successive values. Figure 6. Experimental Setup DS1104 R&D Controller Board ALTERA Cyclone III FPGA DEO Board Gate Driver Circuits Inverter Three-Phase Resistive-Inductive load ∆ Isolated DC Supplies 4-bit 3-bit 1-bit 1-bit 1-bit ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ControlDesk Graphical Programming Approach Observation/analysis via Oscilloscope
  • 9.  ISSN: 2088-8694 IJPEDS Vol. 6, No. 4, December 2015 : 906 – 918 914 4.2. Altera FPGA DEO Controller Board The Altera Field Programmable Gate Arrays (FPGA) DEO Controller Board is known to have high- speed clock which is superior to execute logical or digital operation. From Figure 6, it can be seen that the FPGA receives information of sector (3-bit), triangle ∆ (4-bit) and pre-switching states , and in digital Gray code. The FPGA is responsible to perform the task of selection of appropriate switching states based on the information received. In practice, it is compulsory to provide blanking time for upper and lower IGBTs switching operation to avoid short circuit conditions. The blanking time is set approximately at 2 by selecting appropriate threshold value to be compared with counters, implemented in FPGA. For convenience, the operation of blanking time generation for one leg of any or -phase is described, with the aid of the block diagram and timing diagram, as illustrated in Figs. 7 and 8, respectively. From Figure 7, it can be noticed that the signal is the switching state for -phase which is obtained from the voltage vectors selection table, as mentioned above. The block of MOD18 is assigned to divide the general clock frequency of FPGA 33.33 by 18, hence the new clock frequency becomes 1.85 (or the new period 540 ). The new clock frequency signal is designated as as shown in Figure 7. The new clock frequency signal is used to count up the upper counter (or the lower counter) by 1 for every 540 when is active high (or active low), otherwise both counters will be reset to zero. Note the outputs of upper and lower counter are designated by the respective signals and . By comparing signals a and d with a constant value of 4, the blanking time is approximated to 2 . Increasing or decreasing the constant value of 4 will enlarge or reduce the blanking time, respectively. Note that, the signals and ̅ are for the upper and lower IGBTs of a leg of -phase of VSI. The blanking time generator is duplicated for the other phases and legs to perform the same effect. Then the outputs of switching states from the blanking time generator are then fed to the gate driver circuits. 540ns h a 4 d ̅ 4 Figure 8. Timing Diagram of Blanking Time Generation for -Phase and Any Leg Clk MOD 18 Upper Counter Clk Clear1 Lower Counter Clear1 Comparator ClkClock h a 16-bit d 16-bit Cout1 Cout4 Clkout uc1 lc1 Cin1 Cin4 ̅ 4Cinif 4Cinif 0 1 Cout       Figure 7. Block Diagram of Blanking Time Generation for -Phase and Any Leg
  • 10. IJPEDS ISSN: 2088-8694  Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi) 915 4.3. Power Inverter and Gate Driver Circuits Figure 9 depicts a gate driver and power inverter circuits which are used to produce desired output voltages. The purposes of using gate driver circuits are to provide isolation between the electronic control circuits and power inverter circuits and to provide sufficient power amplification for switching IGBTs. It can be noticed from Figure 9, there are six units of H-Bridge inverter circuits to establish five-level CHMI. Each H-Bridge inverter circuit is supplied by an isolated DC voltage supply. From this figure, it also shows that the FPGA controller board and I/O interface DS1104 card. 4.4. Three-Phase and Series Connected Resistive and Inductive Loads A three-phase and series connected resistive and inductive load is employed for analyzing the performance of SVM for two-level, three-level and five-level of inverters. The load is represented by a load reactor model MV 1101 from TERCO, where its specification and rated condition are given in Table 1. Table 1. Load Reactor Parameters Parameters Value Rated Reactive Power 2.5kVAr Frequancy 50-60Hz Rated Voltage 380V Y, 220V Y/∆ Rated step regulation 287.81mH , 28.082 Ω 5. RESULT ANALYSIS OF TOTAL HARMONIC DISTORTION (THD) OF OUTPUT VOLTAGE This section evaluates the total harmonic distortions (THD) of output voltage and the accuracy of fundamental output voltage of three-level inverters. The evaluation is based on the simulation results (i.e. the values of THD and fundamental output voltage are obtained using Fast Fourier Transforms (FFT) analysis), as well as comparison with the experimental results. The evaluation on THD of output voltage and the accuracy of fundamental output voltage resulted in every level of inverter is also carried out at different modulation indices, 0.3 and 0.9. The simulation results obtained from the evaluation are demonstrated in Figs. 10. From these figures, it can be observed that the experimental results are in close agreements with the simulation results. Specifically, the patterns of wave shape and frequency spectrum of output voltages in the experimental results are similar to that obtained in the simulation results. The similarities between simulation and experimental results, allow the results of THD and fundamental output voltage obtained via simulation to be assumed similar with that of experimental results with the error between the simulation and calculated values is insignificant and approximately less than 1 %. Figure 9. Photograph of FPGA, Gate Driver Circuits and Cascaded H-Bridge Multilevel Inverter (CHMI) FPGA Gate D i CHMI I/O Interface DS1104
  • 11.  ISSN: 2088-8694 IJPEDS Vol. 6, No. 4, December 2015 : 906 – 918 916 6. CONCLUSION This paper presented a technique to implementation the space vector modulator scheme for multilevel inverters. The designs structure is built to minimize the mathematic algorithms in order to ease the implementation in hardware. The scheme contains simple althorithm to interpret the on duration and duty ratio which it all based on the two levels SVM. The implementation required less memory and can be computationally fast. The scheme can perform very well for any reference vector with any modulation index and can easily be extended to any levels. The simulation result with FFT analysis and experiment result has verified the proposed SVM development. ACKNOWLEDGEMENTS The authors would like thanks the Ministry of Education Malaysia (KPM) and Universiti Teknikal Malaysia Melaka (UTeM) for providing the research grant FRGS/2013/FKE/TK02/02/1/F00159 for this research. REFERENCES [1] Holtz, J., W. Lotzkat, and A.M. Khambadkone, On continuous control of PWM inverters in the overmodulation range including the six-step mode. Power Electronics, IEEE Transactions on, 1993. 8(4): p. 546-553. [2] Tripathi, A., A.M. Khambadkone, and S.K. Panda, Stator flux based space-vector modulation and closed loop control of the stator flux vector in overmodulation into six-step mode. Power Electronics, IEEE Transactions on, 2004. 19(3): p. 775-782. [3] van der Broeck, H.W., H.C. Skudelny, and G.V. Stanke, Analysis and realization of a pulsewidth modulator based on voltage space vectors. Industry Applications, IEEE Transactions on, 1988. 24(1): p. 142-150. [4] Adeel, M.S., T. Izhar, and M.A. Saqib. An efficient implementation of the space vector modulation based three phase induction motor drive. in Electrical Engineering, 2009. ICEE '09. Third International Conference on. 2009. [5] Mohamed, A.S.A. and M.R. Baiju. A Novel Space Vector PWM Scheme for Multilevel Inverters. in Applied Power Electronics Conference and Exposition, 2009. APEC 2009. Twenty-Fourth Annual IEEE. 2009. [6] Meng, Y., Z. Liu, and Y. Su. A novel SVM method for three-level PWM voltage source inverter. in Industrial Electronics Society, 2004. IECON 2004. 30th Annual Conference of IEEE. 2004. (a) (b) Figure 10: Simulation and Experimental Results of Phase Voltage and its Frequency Spectrum when Modulation Index a 0.3 and (b) 0.9
  • 12. IJPEDS ISSN: 2088-8694  Implementation of Space Vector Modulator for Cascaded H-Bridge Multilevel Inverters (Syamim Sanusi) 917 [7] Ishida, T., et al. A control strategy for a five-level double converter with adjustable DC link voltage. in Industry Applications Conference, 2002. 37th IAS Annual Meeting. Conference Record of the. 2002. [8] Mondal, S.K., J.O.P. Pinto, and B.K. Bose, A neural-network-based space-vector PWM controller for a three-level voltage-fed inverter induction motor drive. Industry Applications, IEEE Transactions on, 2002. 38(3): p. 660-669. [9] Celanovic, N. and D. Boroyevich, A fast space-vector modulation algorithm for multilevel three-phase converters. Industry Applications, IEEE Transactions on, 2001. 37(2): p. 637-641. [10] Sanmin, W., et al. A general space vector PWM control algorithm for multilevel inverters. in Applied Power Electronics Conference and Exposition, 2003. APEC '03. Eighteenth Annual IEEE. 2003. [11] Gupta, A.K. and A.M. Khambadkone, A General Space Vector PWM Algorithm for Multilevel Inverters, Including Operation in Overmodulation Range. Power Electronics, IEEE Transactions on, 2007. 22(2): p. 517-526. [12] Haoran, Z., et al., Multilevel inverter modulation schemes to eliminate common-mode voltages. Industry Applications, IEEE Transactions on, 2000. 36(6): p. 1645-1653. [13] Jae Hyeong, S., C. Chang Ho, and H. Dong-Seok, A new simplified space-vector PWM method for three-level inverters. Power Electronics, IEEE Transactions on, 2001. 16(4): p. 545-550. [14] Poh Chiang, L. and D.G. Holmes, Flux modulation for multilevel inverters. Industry Applications, IEEE Transactions on, 2002. 38(5): p. 1389-1399. BIOGRAPHIES OF AUTHORS Syamim Sanusi was born in 1986 in Kuala Kerai, Kelantan, Malaysia. She received B.Eng. degree (Hons) from the Universiti Teknikal Malaysia Melaka, Malaysia in 2011 and is currently pursuing the M.Sc degree in the same University. Her area of research interest includes pulse width modulation, space vector modulation and multilevel inverters. Auzani Jidin received the B.Eng. degrees, M.Eng.degrees and Ph.D. degree in power electronics and drives from Universiti Teknologi Malaysia, Johor Bahru, Malaysia, in 2002, 2004 and 2011, respectively. He is currently a Lecturer with the Department of Power Electronics and Drives, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka, Durian Tunggal, Malaysia. His research interests include the field of power electronics, motor drive systems, field-programmable gate array, and DSP applications. Tole Sutikno is an expert in the field of power electronics, Industrial Electronics & Informatics, Embedded Systems and Electric Drives. Since 2001 he has been a lecturer in Electrical Engineering Department, Universitas Ahmad Dahlan (UAD), Indonesia. He is an Associate Professor at the above University since 2008. He is an Editor-in-Chief of TELKOMNIKA Indonesian Journal of Electrical Engineering, and also acts as an Editor in some international journals in electrical and computer engineering, power electronics, motor drive systems and FPGA applications areas Kasrul Abdul Karim received the M.Sc. from University of Bradford and Ph.D. degrees from the University of Nottingham, UK, in 2003 and 2011, respectively. He is currently a Lecturer with the Department of Power Electronics and Drives, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka, Durian Tunggal, Malaysia. His research interests include electrical machine design, power electronics, and electric vehicle.
  • 13.  ISSN: 2088-8694 IJPEDS Vol. 6, No. 4, December 2015 : 906 – 918 918 Siti Azura Binti Ahmad Tarusan received B.Eng. degree (Hons) from the Universiti Teknologi Malaysia, Malaysia and M.Sc. in Industrial Electronics & Control Engineering from University Malaysia, Malaysia. She is currently a Lecturer with the Department of Power Electronics and Drives, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka, Durian Tunggal, Malaysia. Her research interests include power electronic & drive, electrical drive, renewable energy. Mohd Luqman Mohd Jamil received the M.Sc. from Newcastle university, UK and Ph.D. degrees from the The University of Sheffield, UK, in 2003 and 2011, respectively. He is currently a Lecturer with the Department of Power Electronics and Drives, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka, Durian Tunggal, Malaysia. His research interests include power electronics, design and analysis of electric machines and also motor drives