COMPARISON OF VARIOUS MULTILEVL INVERTER CONFIGURATIONS
FOR SEVEN LEVELS
P. V. NARASIMHARAO1, PRABHAKARA SHARMA. PIDATALA2, B. S. S. G. PARDHU3 & P. ANEELA RANI4
1Assistant Professor, Department of Electrical and Electronics Engineering, Vishnu Institute of Technology,
Bhimavaram, West Godavari, Andhra Pradesh, India
2Assistant Professor, Department of Electrical and Electronics Engineering, Kallam Harnadhareddy Institute of
Technology, Prattipadu, Guntur Andhra Pradesh, India
3Assistant Professor, Department of Electrical & Electronics Engineering, Aditya Engineering College,
Peddapuram, East Godavari, Andhra Pradesh, India
4Assistant Professor, Department of Electrical & Electronics Engineering, Akula Sree Ramulu College of Engineering,
Tanuku, West Godavari, Andhra Pradesh, India
ABSTRACT
This concept mainly deals with the multilevel inverter to increase levels using cascade h-bridge concept.
This paper, dissimilar configuration based on different DC bus voltage for a cascade H-Bridge multilevel inverter have
been existing. Four different type techniques symmetrical, asymmetrical, Number of switches is minimised or reduced, and
multi string actions of a seven-level cascade H-Bridge inverters have been compare, in order to find an optimum bargain
with lower switching losses and optimized output voltage excellence. The similarity results show that an asymmetricalconfiguration can obtain more voltage levels in output voltage with same number of component compared with the
conservative seven-level inverter and this will lead to the less number of harmonic content of output voltage.
The compensation of this control method are simplicity and applicability for n-level multilevel inverters, without a major
change in the control circuit.
KEYWORDS: H-Bridge Multilevel Inverter, Total Harmonic Distortion and Switching Losses
INTRODUCTION
In future the power-handling capabilities of static switch devices such as IGBTs with voltage rating up to 4.5 kV
commercially available, has made the use of the voltage source inverters (VSI) possible for high-power applications.
High power and high-voltage changes systems have turn into very important issues for the power electronic manufacturing
handling the huge ac drive and electrical power applications at equally the transmission and sharing levels. For these
reasons, a new family of multilevel inverters has emerged as the solution for working with upper voltage levels.
Multilevel inverters include an array of power semiconductors and capacitor voltage sources, the output of which generate
voltages with stepped waveforms. Capacitor, batteries storage, and RES voltage sources are used as the several dc voltage
sources.
The switching frequency is limited by switching losses are used in the applications of high power and high
voltage applications, multilevel inverters have set up wide acceptance as they can reach low harmonic component with low
International Journal of Electrical and Electronics
2 P. V. Narasimharao, Prabhakara Sharma Pidatala, B. S. S. G. Pardhu & P. Aneela Rani
Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0
switching frequency. still low blocking voltage the main advantage is switching devices and the above switching device is
the other type of converters and minimum harmonic distortion (THD) and switching losses are increased.
Multilevel inverters are mainly used to produce a required voltage wave shape from so many levels of dc voltages.
Their major advantages are low harmonic distortion percent of the getting output voltage, low electromagnetic emissions,
high efficiency ability to perform at high voltages and modularity. The topology assumed for this concept is the cascaded
H-bridge multilevel inverter which requires so many separate dc sources.
In cascaded multilevel inverter each individual phase requires “n” dc sources for 2n+1 level. We getting the level
to use that dc sources, for so many applications, multiple dc sources are required difficult lengthy cables and this could
lead to voltage disturb among the dc sources. With an aim to lessen the number of dc sources required for the cascaded
multilevel inverter for a motor drive, in this paper the main concept is sources and focuses on difference between
asymmetric and symmetric cascade multi level inverter that uses same and unequal dc sources in each phase to generate a
seven level equal step multilevel output. It means less switching losses for the equivalent total harmonic distortion. It alsoimproves the dependability by decreasing the number of dc Sources when comparing symmetrical H-Bridge multi level
inverter.
The MLI modulation technique increases the output voltage and gives a low THD of a relative evaluation between
the VAIS pulse width modulation and the conventional modulation is also existing in terms of output voltage quality,
power circuitry complexity, and total harmonic distortion (THD), Both the MLI circuit topology and its new manage
format are described in detail and their performance is verified based on Matlab/simulation software.
MULTILEVEL INVERTER
Negligible number in multilevel converter topologies is three level voltage levels. Due to the bi-directional
switches, in both rectifier and inverter modes in these two modes the multilevel VSC can work. This is reason most of the
time it is preferred to as a converter instead of an inverter in this dissertation. A multilevel converter can switch either its
input or output nodes (or both) between multiple (more than two) levels of voltage or current. As the number of levels
reach infinity, the output THD reaches to zero. The number of the possible voltage levels, is limited by voltage unbalance
problems, voltage clamping requirements, circuit plan and covering constraints difficulty of the controller, and, of course,
capital and preservation costs. In industrial applications three different major multilevel converter structures have been
applied: cascaded H-bridges converter with different dc sources, diode clamped, and flying capacitors. The multilevel
inverter structures are the main focus of discussion in this chapter; however, the illustrated structures can be implementedfor rectifying operation as well. Although each type of multilevel converters share the advantages of multilevel voltage
source inverters, they may be suitable for specific application due to their structures and drawbacks. Operation and
structure of some important type of multilevel converters are discussed in the following sections.
In a multilevel voltage source inverter, the dc-link voltage Vdc is obtained from any equipment which can yield
stable dc source. Series connected capacitors constitute energy tank for the inverter provided that a few nodes to which
multilevel inverter can be connected. First and foremost, the series connected capacitors will be supposed to be several
voltage sources of the same value. Every one capacitor voltage Vc is given by Vc=Vdc/ (n-1) calculated this formulae,
where n denotes the number of level. The schematic diagram of one phase leg of inverters with dissimilar number of levels,
for which the action of the power semiconductors is represents by a perfect switch with a number of positions.
8/10/2019 1. Electrical - Ijeeer - Comparison of Various - Vamsi
4 P. V. Narasimharao, Prabhakara Sharma Pidatala, B. S. S. G. Pardhu & P. Aneela Rani
Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0
Table 1 shows the switching combinations that generated the seven output-voltage levels (Vdc, 2Vdc, 3Vdc,
0,-Vdc,-2Vdc,-3Vdc).
Asymmetrical Configurations
The seven - level cascaded multilevel inverter presents two H-Bridges in each bridge 4 switches presents total
8 switches are present. The upper bridge indicates H-Bridge H1consists of a separate DC source V dc and the second
H-Bridge H2consists of a dc source 2Vdc as shown in below figure. The output of H-Bridge-1 be denoted as V1 and the
output of H-Bridge-2 be denoted as V2 Hence the total output voltage is given by V (t) =V1 +V2 By one another ON and
OFF the switches S1, S4 and S2,S3 of H-Bridge-1 appropriately, output of H1 V1 can be made equal to +Vdc, 0 or -Vdc.
Similarly the output voltage of H-Bridge-2 V2 can be made equal to –2Vdc, 0 or 2Vdc by opening and closing the switches
of H2.
Figure 3: Asymmetric Cascaded Multilevel Inverter
The advantages of the topology are:
• Reduced number of dc sources.
• High speed capability
• Low switching loss
• High conversion efficiency.
Table 2: Output Voltage According to the Switches’ On–Off Condition
Vo S1 S2 S3 S4 S5 S6 S7 S8
Vdc On On Off Off On Off On Off
2Vdc On Off On Off On On Off Off3Vdc On On Off Off On On Off Off
0 On Off On Off On Off On Off
-Vdc Off Off On On On Off On Off
-2Vdc On Off On Off On On Off Off
-3Vdc On On Off Off On On Off Off
Reduced Number of Switches
The main objective is to improve the quality output voltage of the multilevel inverter with reduced number of
switches. An important issue in multilevel inverter design is that to generate nearly sinusoidal output voltage waveform
and to eliminate lower order harmonics. A key concern in the fundamental switching scheme is to determine the switchingangles in order to produce the voltage with fundamental frequency.
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There are three modes of operation for the proposed 7-level multilevel inverter. These modes are explained as
below.
Powering Mode
This occurs when together the load current and voltage have the same polarity. In the positive half cycle, when the
output voltage is Vdc, the current pass comprises; the below supply, D6, Switch-1, load, Switch-2, and back to the lower
supply. When the output voltage is 2Vdc, current pass is; the lower source, S5, the upper source, Switch-1, load, Switch-2,
and back to the lower source. When the output voltage is 3Vdc, the current pass comprises: top supply, Switch-1, load,
Switch-2, S7, lower supply. In the negative half cycle, Switch-1 and Switch-2 are replaced by Switch-3 and Switch-4
respectively.
Free-Wheeling Mode
This mode exist one of the main switches is turned-off while the load current needs to continue its pass due toload inductance. This is achieved with the help of the anti-parallel diodes of the switches, and the load circuit is no
connection from the source terminals. In this mode, the positive half cycle current pass comprises; Switch-1, load,
and Diode-2 or Switch-2, load, and Diode-3, while in the negative half cycle the current pass includes Switch-4, load,
and Diode-4 or Switch-3, load, and Diode-1. Regenerating Mode In this mode, part of the energy stored in the load
inductance is return back to the source. This happens during the intervals when the load current is negative during the
positive half cycle and similarly, where the output voltage is zero. The positive current pass comprises; load, Diode-2,
Switch-6, the lower source, and Diode-3, while the negative current pass comprises; load, Diode-1, Switch-6, the lower
source, and Diode-4.
Table 3: Output Voltage According to the Switches’ On–Off Condition
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