DESIGNING A LARGE AUTOMOTIVE ELECTRIC VEHICLE BY USING T TYPE MULTILEVEL INVERTERS

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 10 Issue: 03 | Mar 2023 www.irjet.net p-ISSN: 2395-0072
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DESIGNING A LARGE AUTOMOTIVE ELECTRIC VEHICLE BY USING T
TYPE MULTILEVEL INVERTERS
1Mr. Ch. Sai Charan, 2Mrs. T. RAJESWARI
1PG scholar in Holy Mary Institute of Technology & Science, Bogaram (V), Medchal District, Hyderabad, India in the
Dept. of Electrical & Electronics Engineering.
2Assistant Professor in Holy Mary Institute of Technology & Science, Bogaram (V), Medchal District, Hyderabad, India
in the Dept. of Electrical & Electronics Engineering.
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Abstract - The major goal of this research is to develop a
bidirectional T-type multilevel inverter based on space
vector pulse width modulation (SVPWM) for electricvehicle
applications. A bidirectional multilayer dc-dc converter is
used in this project, which is a need in electric vehicles. To
balance the voltage of the T-type multilayer inverter (MLI)
capacitor across a complete drive cycle or at-faultsituations,
the proposed one simply needs two extra power switches
and a capacitor. Space vector pulse-width modulation
(SVPWM) is one of the most used modulation techniques for
a multilevel inverter. The SVPWM for a multilevel inverter,
on the other hand, is difficult to execute. The difficulty in
finding the location of the reference vector, calculating on-
times, and defining and selecting switching states
contributes to the complexity. Based on typical two-level
SVPWM, this study presents a general SVPWM algorithmfor
multilayer inverters. Thelargeelectrolytic capacitorsusedin
T-type MLI are replaced with more dependable, longer-life
film capacitors in this configuration due to the high-
frequency cycle-by-cycle voltage balance between CN and
CP. The converter's size and weight will be reduced by 20%
as a result of this. This frees up additional space in the
chassis' space envelope for the EV battery, allowing it to
grow in capacity. THD and line voltages are more rippled in
the current system. The SVPWM approach is used to reduce
these difficulties.
Key Words: (T-TypeMultilevel inverter,spacevectorpulse
width modulation (SVPWM), two-level SVPWM.
1. INTRODUCTION
To synthesizes its stepped output voltage levels, multilevel
inverters often use separated dc power sources or split
capacitors coupled to a single dc powersource.Thefirsttype
is more reliable, but it necessitates a greater number of dc
power sources and power switches, such as a cascaded H-
bridge multilevel inverter, as previously mentioned. Split
capacitor-based MLIs,suchastheneutral pointclamped NPC
MLI [4], flying capacitor FC MLI [5], and T-type MLI [6] [7],
on the other hand, required less power components.
However, because the voltage across each capacitorisbased
on an ideal natural balance, their voltages are vulnerable to
voltage drifting, resulting in voltage imbalance operations.
The three-phase inverter in thepropulsionsystemofelectric
vehicles is fed by a bi-directional DC-DC converter [8] [9]
[10]. It regulates the dc bus voltage to the level required to
allow power to flow to the electric machine in driving mode
over the designated modulation index range (mmmm). The
bi-directional converter stepped the DC voltage in breaking
mode (regenerative) to let power to flow in the opposite
direction from the electric machine back to the utilitygrid or
electrical storage units, as in an electric vehicle. The bi-
directional converter can be built as a boost converter in
motoring mode and a buck converter while braking, or vice
versa, depending on the power source connected to the
propulsion system.
The on-times can be obtained in one of two ways. The first
method is to find the triangle and then solve three
simultaneous equations for it to get the on times, as shown
in [4]. The second way, as shown in [5, is to determine the
triangle and then use the specific on-time equations
contained in the lookup for this triangle. Both of these
systems, however, become computationally costly as the
number of levels rises. The works [6] and [7] offered a
general approach for obtaining on-times for multilayer
inverter SVPWM in the linear modulation range [8].
Celanovic and Boroyevich [6] offer a Euclidean vector
system-based SVPWM technique that is rather complicated
due to the utilization of multiple matrix transformations.
Furthermore, neither [6] nor [7] give a systematic method
for finding the switching states, nor a real-time
implementation. Wei et al. [7] suggest a method that is a
modified version of the system in [6]. To calculate on-times
and determine switching states, this approach use the 60
coordinate system. The 60 transformation adds to the
complexity because most control methods supply a voltage
reference in coordinates. The SVPWM for a multilevel
inverter is performed using a simple approach proposed in
this paper. The technique is based on two-level SVPWM and
may be built for any level with just one counter. Using the
two-level approach, some studies [9]–[11] proposed
multilevel SVPWM. However, these methods have some
flaws that are addressed in the suggested strategy. Zhang et
al. [9] offer a method for on-time calculation based on two-
level simplification, in which the three-level space vector
diagram is reduced into six two-level space vectordiagrams.

A segregation of the three-level space vector diagram yields
the locations of the centers of six virtual hexagons. To
employ two-level on-time calculation, the origin is virtually
relocated to one of the six centers, and the axes are rotated
by 60 degrees. This strategy works effectively for three
levels because only three levels require segregation. Is it
possible to extend this strategy to higherlevels?Theon-time
calculation for level n > 3 is not included in [9].
This work takes a different approach than all of the previous
references and offers a general answer. It is based on a
traditional Cartesian coordinate system, therefore it may be
simply integrated with existing speed or torque outer
control loops. The key features of the proposed plan are
listed below.
1) Due to the usage of two-level SVPWM, the on-time
computation is straightforward. Because the on-time
calculation formulae do not change with the position of the
reference vector, as in the old approach [5], no lookuptables
are required.
2) The triangle where the reference vector is positioned in
the space vector diagram of an n-level inverter is identified
as integer j using a simple algebraic expression. The jth
triangle among the (n 1)2 triangles in a sector is referred to
as the triangle number j. With respect to triangle j, any
switching sequence can be implemented, resulting in ease
and flexibility in optimizing the switching sequence.
3) Without significantly increasing computations, the
proposed approach can be applied for any n-level (n 3)
inverter.
4) The proposed system is simple to implement using a
commercially available motion-control DSP or
microcontroller, which typically only supports two-level
modulation. The technique is described in detail for a three-
level inverter before being generalized to any level. For
three-level and five-level inverters, experimental findings
are reported.
Fig.1 Proposed configuration of a multilevel bidirectional
dc–dc converter connected to the T-type MLI
II. PROPOSED SCHEME
A. Proposed Method of On-Time Calculation for a
Multilevel Inverter
The core idea behind SVPWM is to use discrete switching
states and their on-times to compensate for the required
volt-seconds.Threesimultaneousequationsaretraditionally
solved to calculate the on-times for a triangle of an n-level
inverter.
However, a classical two-level space vector geometry canbe
used for on-time calculation for a multilevel SVPWM. Fig. 2
shows the space vector diagram of a two-level inverter. √
Every sector is an equilateral triangle of unity side and h(=
3/2) is the height of a sector.
Fig. 2. Space vector diagram for two-level inverter.
On-time calculation for any of the six sectors Si, i = 1, 2,..., 6 is
same, so let us consider the operation in sector 1. On-time
calculation is based on the location of the reference vector
within a sector. For the sector 1 in Fig. 3, the volt-second
balance is given by
Time balance is given by
Resolving (1) along the αo − βo axis, we obtain.
Solving (2)–(4), we obtain the following equations for the
calculation of the on-times:

Fig. 3illustrates the proposed method of the on-time
calculation for a three-level inverter. Each sector of a three-
level inverter can be split into four triangles j , where j = 0, 1,
2, 3. To simplify the on-time calculation, these triangles can
be categorized into two types; type 1 andtype2.Atriangleof
type 1 has its base side at the bottom, as shown in Fig. 3(b).
Triangles 0, 1, and 3 are of type 1. A triangle of type 2 has its
base side at the top, as shown in Fig. 3(d). Triangle 2 is of
type 2.
Fig3. Space vector diagram—virtual two-level from three-
level.
Let us assume that the side of a triangle is 1(unity) and h(=
√3/2) is the height of the triangle. In Fig. 4(a), v∗ is the
reference vector of magnitude |v∗| at an angle of γ with the
α-axis. We define a small vector vs,whichdescribesthesame
point in shifted system (αo, βo) [see Fig. 4(b) and (d)]. It
makes γs angle with the αo axis. The volt-seconds required
to approximate the small vector vs in the shifted system(αo,
βo) should be equal to those requiredfortheactual vectorv∗
in the original system (α, β). Hence, we can obtain the on-
times for any reference vector by finding the on-times of the
respective small vector vs.
To achieve the volt-seconds for any reference vector in a
sector of a three-level inverter, we have to identify the
triangle in which the required reference is located and then
find (vs αo, vs βo). The on-time calculations can be
performed using the geometry shown in Fig. 3(b) or (d),
which would result in the same on-time equations as those
for a classical two-level SVPWM (5)–(7). A triangle of type 1
is similar to a sector 1 of a virtual twolevel inverter.
For example; In Fig. 3(a), triangle 3 can be assumed similar
to sector 1 of a two-level inverter if A2 is taken as zero
vector of the virtual two-level sector as shown in Fig. 3(b).
Vector A2P defines the small vector vs(vs αo, vs βo). On-
times ta (tA4 ), tb (tA5 ), and to (tA2 ) are calculated byusing
(5)–(7), where the multiplication operations are required
only for (5) and (6). A triangle of type 2 is similar to a sector
4 of a virtual two-level inverter. For example; In Fig. 3(c),
triangle 2 can be considered similar to sector4ofa two-level
inverter if A4 is assumed to be zero vector [see Fig. 4(d)]. In
this example, A4P represents small vector vs(vs αo, vs βo).
On-times ta (tA2 ), tb (tA1 ), and to (tA4 ) are calculated by
using (5)–(7).
Fig. 4. Block diagram of SVPWM control
Since the triangles within any sector of an n-level inverter
are analogous to a sector of two-level inverter, the idea can
be extended to any level.Thus,multilevel on-timecalculation
problem is converted to a two-level on-time calculation
problem. The on-times ta, tb, and to are a function of (vs αo,
vs βo) for any triangle, using (5)–(7). Therefore, the on-time
calculation for one triangle can also be used for any other
triangle.
Block-Diagram Explanation of the Scheme Block diagram in
Fig. 5 gives an overview of the proposed method. It consists
of two basic units, namely primary unit (PU) and secondary
unit (SU), respectively. The PU consists of a preprocessing
unit and two-level SVPWM unit. The PU is basically a DSP or
microcontroller. The preprocessing unit does two main
tasks: 1) determination of small vectorvscoordinates(vsαo,
vs βo) and 2) determination of the sector Si and thetrianglej
of the small vector vs. Two-level SVPWMunitobtainsthe on-
times to, ta, and tb by using (5)–(7). The SU is basically a
mapping unit and uses memory. It fires the three-phase
inverter's pre-stored switching sequence based on sector Si,
triangle j for the on-times obtained from the PU. A vertex of
any triangle can have many redundancies for a multilayer
inverter (two or more possibleswitchingstates).Aswitching

sequence for a triangle is created by combining the most
appropriate switching states from all potential switching
states at the vertices. With respect to the triangle and sector
number, the resulting switching sequence is mapped. The
on-times collected from the PU are then used to fire the
switching sequence. Because the suggested technique
considers the triangle to be the fundamental unit and the
mapping eliminates redundancies,anysuitablevertexcan be
chosen as the zero vector.Redundanciesatothervertices are
also used in this process. The order in which the on-timesta,
tb, and to must be employed is determined by the order in
which the switching states are selected. As a result, any
redundancy for any vertex of the triangle can be used by the
suggested technique. In contrast, when the two-level
hexagon is employed to simulate two-level modulation, just
two zero vector redundancies are considered. As a result, at
a higher level, where middle vectors have moreredundancy,
such an approach will be ineffective.
III. Results
Fig. 5. single-phase line-to-line output voltage.
Fig. 6. Inverter currents
Fig. 7. Motor current in regenerative mode
Fig8. Motor Speed varies from 900rpm to 1500rpm at
t=0.45 sec and again drops to 300rpm at t= 0.75s.
As shown in generalized multilevel inverter configuration
with the SVPWM technique it controls the motor THDs and
the inverter switching pulse.
Conclusion
This research describes a new integration of a modified bi-
directional dc-dc multilevel converter with a five-level T-
type multilevel inverter for electric car applications. In
comparison to a traditional voltage source inverter, the T-
type MLI uses more power switches. It uses power switches
with half the peak inverse voltage to provide a greater
variety of output voltage levels. A simple SVPWM algorithm
based on a regular two-level inverter has beenpresented for
a multilevel inverter. Level has no effect on the
computations. A commercially availablemotion-control DSP
or microcontroller, which generally only supports two-level
modulation, can simply implement the proposed technique.
The suggested technique has the benefit over previous
approaches in that it can be employed with an existing
torque or speed control technique based on two-level
geometry. Because such systems give a voltage reference in
coordinates, the suggested method makes extensive use of
two-level calculations and may be applied to any n-level
inverter. Furthermore, the peak inverse voltage of all power
switches and the rated voltage of all capacitors are both
limited to half of the peak ac outputvoltage, reducing voltage
stress, and allowing higher efficiency power switches in the
dc-dc side, similar to those in the T-type MLI side, to be
implemented.
REFERENCES
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AUTHOR DETAILS’:
Mr. Ch. Sai Charan received a B. Tech
Degree in Electrical and Electronics
Engineering from JNTUH College of
Engineering Manthani, Pannur(V),
Ramgiri(M), Peddapalli(D), Telangana,
India, and is Studying M. Tech in Power
Electronics at Holy Mary Institute of
Technology and Science, Bogaram(V),
Medchal (D), Hyderabad, India.
Mrs. T. RAJESWARI received the
B.TECH degree in EEE from Sridevi
women’s engineering college,
V.N.Pally, College Rd, Gandipet,
Telangana, INDIA, from JNTU
University and MTECH in Electrical
Power Systems in Tirumala
engineering college, Bogaram (v), Medchal(D), Hyderabad,
Telangana, INDIA. She has 1-yearindustrial experienceand5
years of teaching experience. Currently pursuing Ph.D in SR
University and working as an Assistant professor at Holy
mary Institute of Technology and sciences, Bogaram,
Medchal District, Hyderabad, Telangana, INDIA in EEE
department. Her interest areas are FACTS, Computer aided
power system analysis, electrical distribution systems,
Power electronics etc.

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