International Journal of
Applied Sciences, Engineering and Technology
Vol. 02, No. 01, Jan-Dec 2013
Performance of a 5-Level Hybrid Multilevel power conversion System Fed
Induction Motor Drive
S. ANUSHA and P. V. V. RAMA RAO
Department of Electrical & Electronics Engg. Shri Vishnu Engg. College for Women, A.P., India
Email: s.anusha202@gmail.com, hodeee@svecw.edu.in
Abstract: The Multilevel inverters (MLI) are a new breed of power converter that is suited for high power
applications. This paper presents three-phase cascaded hybrid multilevel inverter for 5-level has been developed
from a conventional cascaded multilevel inverter. It consists of a standard 3-leg inverter (one leg for each phase) and
H bridge in series with each inverter leg with separate dc voltage source, the three-phase induction motor as a load.
Also the proposed topology can reduce the number of power switches compared to a traditional cascaded multilevel
inverter. The modified PWM technique is introduced to the hybrid multilevel inverter topology which reduces the
number of controlled switches used in the system. Due to the involvement of high number of switches thereby the
harmonics, switching losses, cost and the THD is increased. This proposed topology increases the level with less
number of switches. It dramatically reduces the switches for high number of levels that reduces the switching losses,
cost and low order harmonics. Simulation has been carried out in MATLAB/simulink to study the performance of
the proposed topology
Keywords: Cascaded H-bridge, Hybrid 5-level inverter, SPWM technique, Modified PWM technique.
Introduction:
Use of multilevel inverters has become popular in recent
years for high-power applications [1], and is very
promising in ac drives, when both reduced harmonic
contents and high power are required. A multilevel
inverter is a power electronic system that synthesizes a
desired output voltage from several levels of dc voltages
as inputs [2]. By synthesizing the AC output voltage
from several levels of DC voltages, staircase output
voltage waveform can be produced. This allows for
higher output voltage and simultaneously lowers the
stress on the semiconductor devices. Among the various
topologies of the multilevel inverters; cascaded H-bridge
and the hybrid inverter requires two DC sources [3]. The
number of power switches required for the multilevel
inverters is shown Fig.1. Several well known pulse
width modulation methods have been developed for the
multilevel inverter structures [4], which are as follows:
Selective Harmonic Elimination PWM (SHEPWM),
Space Vector PWM (SVPWM) and Sinusoidal PWM
(SPWM) [5]. Among these PWM methods the SPWM is
the most popular one and its popularity is partially due to
its simplicity.
Fig 1.One phase of a 5-level Inverter
a. Cascaded H-bridge b. Hybrid 5-level
inverter
inverter
Table I: Components of a Single-Phase 5-Level Inverter
Types of
No of
No of
multilevel
switches
capacitors
inverter
Cascaded H-bridge
8
-
Cascaded hybrid
6
2
The SPWM for multilevel inverters are categorized in to
two methods: Single Carrier SPWM (SCSPWM) and
Sub Harmonic SPWM (SHSPWM). The modified
PWM technique [6] requires a one reference and a
carrier signal, it is a combination of both sine and the
triangular wave.
Three-phase induction motors are commonly used in
many industries. Generally, DC motors were the work
horses for the Adjustable Speed Drives (ASDs) due to
their excellent speed and torque response [8]. But they
have the inherent disadvantages of commutator and
brushes, which undergo wear and tear. Most of the
cases AC motors are preferred due to its low cost, less
maintenance, lower weight and higher efficiency.
The advantages of multilevel inverters is their smaller
output voltage step, which results in high capability,
lower harmonic components, lower switching losses,
better electromagnetic compatibility and high power
quality [12]. Also it can operate at both fundamental
switching frequency and high switching frequency
PWM.
Today, multilevel inverters are extensively used in
medium voltage levels with high-power applications
IJASET 020102 Copyright © 2013 BASHA RESEARCH CENTRE. All rights reserved.
S. ANUSHA, P. V. V. RAMA RAO
[13]. The field applications include use in laminators,
pumps, conveyors, compressors, fans, blowers and
mills.
In this paper hybrid multilevel inverter is proposed
developed from a conventional cascaded H-bridge
inverter and a modified PWM technique is also
developed to generate the gate pulses.
Cascaded Five-Level Inverter:
A cascaded H-bridge inverter for five levels is shown in
Fig.2. Normally, each phase of a three-phase cascaded
multilevel inverter requires “n” DC sources for 2n+1
level. Each separate dc source is connected to a single
H-bridge inverter.
Vdc
Vdc
, 0,
. Therefore the output voltage of the
2
2
inverter is a combination of V1 and V2 that has 5
Vdc
Vdc
possible values 0,
, Vdc ,
, Vdc , the
2
2
to
switching pattern is given in table II. The model output
voltage as shown in Fig.3.
Fig.3. Output waveform of a 5-level inverter
Fig.2. Three-phase cascaded H-bridge multilevel
inverter
Table II Switching pattern at 8 switches
S.No
Switches
Output Voltage
Levels
1
0
2
V
Fig.4. Subsystem to generate gate pulses in Simulink
using SPWM technique
dc
3
4
5
2
Vdc
Vdc
2
Vdc
Fig.5.Generation of pulses using SPWM technique
A five-level cascaded H-bridge multilevel inverter has
two H-bridges for each phase. The output voltage of the
first H-bridge is denoted by V1 and the output of the
second H-bridge is denoted by V2 , so that the output
voltage of the cascaded multilevel inverter is the sum of
the two voltages Vo  V1  V2 . By opening and closing
of the first bridge appropriately the output voltage
V1
Vdc
Vdc
, 0,
.while the output
2
2
voltage of the second bridge V2 can be made equal
can be made equal to
Carrier based sinusoidal pulse width modulation
(SPWM) is a popular method in industrial applications.
SPWM is used to generate the PWM pulses. The
multicarrier PWM method uses several triangular carrier
signals, keeping only one modulating sinusoidal signal.
If an ‘n’ level inverter is employed, ‘n-1’ carriers will
be needed. The carrier will have the same frequency and
the same peak to peak amplitude as shown in Fig.5. At
every instant the reference is continuously compared
with each of the carrier signal, and then the active
device corresponding to that carrier is switched on, and
if the reference is less than a carrier signal, then the
active device corresponding to that carrier is switched
International Journal of Applied Sciences, Engineering and Technology
Vol. 02, No. 01, Jan-Dec 2013, pp 6-11
Performance of a 5-Level Hybrid Multilevel power conversion System Fed Induction Motor Drive
off. The simulink model to generate the PWM pulses is
shown in Fig.4.
Methodology:
The topology of the proposed hybrid multilevel inverter
is illustrated in Fig.6, includes a standard three leg
inverter (one leg for each phase) and H-bridge in series
with each inverter leg. Before continuing discussion, it
should be noted that the word main inverter is used to
refer to the six-switch three-phase inverter and the word
auxiliary inverter is referred to four-switch H-bridge
inverter. Since the low switching losses during PWM
operation is required, the main inverter will operate on
square wave mode and auxiliary inverter will operate on
PWM mode as depicted in Fig.8. The application of
hybrid multilevel inverter with DC source applied in
vehicle applications.
Hybrid Five-Level Inverter:
The topology of the proposed hybrid multilevel inverter
is shown in Fig.6 which includes a complete and a
simplified single-phase topology. It includes a standard
3-leg inverter (one-leg for each phase) and H-bridge in
series with each inverter leg. The bottom is one leg of a
standard 3-leg inverter with a dc power source ( ), the
top is a H-bridge is connected in series with a 3-leg
inverter use a separate dc power source (
).
achieve as shown in Fig.3, when the output voltage
Vo  V1  V2 is required to be zero, one can either set
Vdc
Vdc
and V2 
2
2
Vdc
.
V2 
2
V1 
or V1 
Vdc
2
and
Table III Switching Pattern at 6 Switches
S. No
On switches
Voltage levels
1
Sa1Sa 2 S6
0
2
Sa1Sa 3 Sa 5
3
Sa1Sa 2 Sa 5
4
5
Sa1Sa 3 Sa 6
Sa 3 Sa 4 Sa 6
Vdc
2
Vdc
Vdc
2
Vdc
Fig.7. Logical diagram
The referent sinusoidal PWM (SPWM) used for the
auxiliary inverter is modified by using equation (1)-(4).
The multiplexing signals from (3) and (4) are used to
fabricate PWM signals by using logic diagram as shown
in Fig.7.
Fig. 6.Topology of a five level three phase cascaded
hybrid multilevel inverter
The output voltage
S a 5 closed or
V1 of this leg is either
Vdc
when
2
Vdc
when S a 6 closed. This leg is
2
connected in series with a full H-bridge inverter, then
the output voltage V2 of the H-bridge inverter is either
Vdc
2
when S a1 , S a 4
when S a1 , S a 3 or S a 2 , S a 4 closed, or
closed,
0
Vdc
when S a 2 ,
2
S a 3 closed the switching pattern is given in table III.
An example output waveform that this topology can
f  t   ma .sin t 
 
1 1
2  f t    ;  f t   1

Tp  
2 2

Tc   1
1

2   f  t   ;0  f  t  
  2
2


1; f  t   0
A1  

0; f  t   0
1

1; f  t   2
A2  
0; f  t   1

2
International Journal of Applied Sciences, Engineering and Technology
Vol. 02, No. 01, Jan-Dec 2013, pp 6-11
(1)
(2)
(3)
(4)
S. ANUSHA, P. V. V. RAMA RAO
Where
is a referent signal,
is modulation index(0.0/1.0-1.0/1.0)
is a multiplexing signal 1,
is a multiplexing signal 2
is pulse width of PWM (0.0-1.0)
Fig.9. Three-phase cascaded H-bridge 5-level inverter
Fig.8. Modulating signals of both main and
auxiliary inverter
Table IV Fabricated PWM Signal for Proposed Hybrid
Multilevel Inverter
Sn
SA1
SA2
SA3
SA4
SA5
SA6
Hybrid PWM mixing operator
A1
Ā1
PWM * ((A2*A1) + (Ā2* Ā1))
PWM’ + ((A2*A1) + (Ā2* Ā1))
PWM * ((A2*A1) + (Ā2* Ā1))
PWM’ + ((A2*A1) + (Ā2* Ā1))
Simulation Results:
A three- phase cascaded H-bridge five level inverter
with dc source simulated and is shown in Fig. 9 and
corresponding five level output voltage waveform is
shown in the Fig.11. Similarly a three-phase cascaded
H-bridge five level inverter using sinusoidal PWM
technique is simulated and is shown in Fig.10 and the
corresponding five level output voltage wave form is
shown in the Fig.12.
Table V Voltages of 5-Level Inverter
Types of
Voltage
Voltage
Voltage
multilevel
V1
V2
V0=V1+V2
inverters
Cascaded H50
50
100
bridge
Cascaded
50
50
100
hybrid
Fig.10. Three-phase cascaded H-bridge 5-level
inverter using SPWM Technique
Fig.11. Output voltage waveform of a three-phase
cascaded H-bridge 5-level inverter
Fig.12. Output voltage waveform of a three-phase
cascaded H-bridge 5-level inverter using SPWM
technique
A three-phase cascaded hybrid 5-level inverter
simulated is shown in Fig.14 and corresponding 5-level
output voltage wave form as shown in the Fig. 16.
Similarly a three-phase cascaded hybrid 5-level
inverter using modified PWM technique simulated and
is shown in the Fig 15 and the corresponding 5-level
output voltage waveform as shown in the Fig. 17 and
the line-line output voltage waveform as shown in the
Fig.18.
International Journal of Applied Sciences, Engineering and Technology
Vol. 02, No. 01, Jan-Dec 2013, pp 6-11
Performance of a 5-Level Hybrid Multilevel power conversion System Fed Induction Motor Drive
motor. The speed of the rotor is nearly 155.3rad/sec as
per the results of speed-time curve, shown in Fig.19 and
the torque during simulation as shown in Fig.20.
Fig.14. Three-phase cascaded hybrid 5-level inverter
Fig.19. Speed-time curve
Fig.20. Torque with respect to time
Fig.15. Three-phase cascaded hybrid 5-level inverter
using Modified PWM technique
Fig.16. Output voltage waveform of a three-phase
cascaded hybrid 5-level inverter
Fig.17. Output voltage waveform of a three-phase
cascaded hybrid 5-level inverter using SPWM technique
Fig.18. Line-line output voltage waveform of a
cascaded hybrid 5-level inverter.
A three-phase asynchronous motor is connected to the
proposed circuit shown in the Fig.14. The circuit is
simulated to show the performance characteristics of
Conclusion:
A three-phase cascaded H-bridge 5-level inverter and a
three-phase cascaded hybrid 5-level inverter are
connected to a three-phase induction motor used as a
load to observe the performance characteristics of the
motor. This paper has demonstrated the state of the art
of modified multilevel inverter topologies with reduced
number of switches. This multilevel inverter structure
and its basic operations have been discussed. The
modified PWM technique has also been developed to
reduce the switching losses. From the simulation results,
several features of the proposed modulation strategy the
output waveform are observed. Also the proposed
topology can reduce the number of required power
switches compared to a traditional cascaded H-bridge 5level inverter to get the same output voltage waveform.
Thus the complexity and the cost of the circuit are
decreased.
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International Journal of Applied Sciences, Engineering and Technology
Vol. 02, No. 01, Jan-Dec 2013, pp 6-11