Development of Multilevel Inverters for Control Applications

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 03 Issue: 01 | Jan-2016 www.irjet.net p-ISSN: 2395-0072
© 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 1068
Development of Multilevel Inverters for Control Applications
Jaya Sree.Lavydya1, Farzana Sayeeda2
12 Asst Prof, Dept of EEE, Cristhu Jyothi Inistitute of Technology & Science, Telengana ,India
Abstract— In the aspect of industrial automation,
inverter plays a vital role in developing drives. With
two-level voltage source inverters to obtain a quality
output voltage or a current waveform with a
minimum amount of ripple content they require high
switching frequency along with various pulse width
modulation (PWM) strategies. In high power and high
voltage applications these two-level inverters have
some limitations in operating at high frequency
mainly due to switching losses and constraints. The
multilevel inverters have drawn tremendous interest
for high voltage and high power applications. This
paper proposes design and implementation of the
sinusoidal pulse width modulation (SPWM) and
multilevel technique to reduce the harmonics. In
developing this technique, intelligent systems is
proposed to improve their performance. The
performance of the proposed technique will be
compared with standard existing techniques. The
design and development of multilevel techniques will
be carried out in Matlab/Simulink environment.
Key words— CHMLI, SPWM, NN
1. INTRODUCTION
From last decades, the multilevel inverters have
drawn tremendous attention in the field of high voltage
and high power applications. In the researches on
multilevel inverters, determination of their respective
control strategies is the emerging topic. Modern power
electronics based devices have put a great effect on the
development of new powerful applications and
industrial solutions. But at the same time, these
advances have increased the harmonic problems in line
currents, which make distortion in the voltage
waveforms. Diode power rectifiers, thyristor converters
and static VAR
compensators (SVCs) are examples of power electronics
applications [6]. The series connection of several bridges
allows working with much higher voltages and the
stepped voltage waveforms to eliminate the voltage
stress in associated equipment, such as transformers [5].
Moreover, the bridges of each converter work at a very
low switching frequency which allows working with low
speed semiconductors and low switching frequency
losses.
Filters are used for compensation of
contaminating load with small power factor and to feed
the load during voltage dips. The multilevel inverters
perform power conversion in multilevel voltage steps to
obtain improved power quality, lower switching losses,
better electromagnetic compatibility and higher voltage
capability. Considering these advantages, multilevel
inverters have been gaining considerable popularity in
recent year.
2. MULTILEVEL INVERTERS
2.1 Types of Multilevel Inverters
Fig - 1: Classification of multilevel inverters

In Figure 1 different types of multilevel
inverters are given. Each multilevel inverter contains
different features and different control schemes and
different structures in themselves. Multilevel inverter
topologies are classified into three categories diode
clamped inverters, flying capacitor inverters and
cascaded inverters [1]. In Diode clamped inverters
clamping diodes per phase, DC bus capacitors, power
semiconductor switches are presented. In flying
capacitor inverters power semiconductor switches, DC
bus capacitors, balancing capacitors per phase are
presented. In cascaded inverters DC bus capacitors,
power semiconductor switches are presented.
2.2 Comparison of Multilevel Inverter Topologies
Total Harmonic Distortion of output voltage. Amplitude
of fundamental and dominant harmonic components.
Number of semiconductor devices used per phase leg.
Control complexity based on voltage unbalances and
power switches [2]. Number of balancing capacitors
used per phase leg. Number of DC bus capacitors used.
Cascaded inverter requires the least number of
components to achieve the same number of voltage
levels in comparison with diode clamped and flying
capacitor inverters. The implementation costs of the
FCMLI and CMLI are almost same but it is fifteen
percentages lower than that of DCMLI. It is found from
above comparison that the cascaded multilevel inverter
topology is the most promising one. Cascaded inverters
provide a compounding of voltage levels leads to lower
harmonic distortion avoids single isolated voltage
sources and constructed with the low rating power
devices which are commercially market ready [3].
2.3 Advantages of Multi Level Inverters
In general, multilevel power inverters can be
view as voltage synthesis in which the high output
voltage is synthesized from many discrete small
voltage levels, main advantages of this approaches are
summarized as follows.
The voltage capacity of the exciting devices can be
increased many times without the complication of
static and dynamic voltage sharing that occurs in
series connected devices. Spectral performance of
multilevel wave forms is superior to that of the two
level counter parts. Multilevel wave forms naturally
limit the problems of large voltage transient that occur
due to the deflections on cables, which can damage the
motor winding cause other problems. To decrease the
THD value [4].
3. CONVENTIONAL CONTROL OF MULTILEVEL
INVERTER
3.1 Five-level Cascaded H-bridge Multilevel
Inverter
This inverter is operated with Vdc = 2V. Figure 2 shows
the circuit diagram of five-level cascaded H-bridge
multilevel inverter simulation model. The pulse pattern
for the circuit is generated by using the sinusoidal pulse
width modulation.
The output responses of model which are voltage and
current waveforms and their THD spectrums are shown
in Figure 3,4,5 and 6 respectively.
4. NEURAL NETWORK CONTROL OF
MULTILEVEL INVERTER
CHMLI block as shown in Figure 7 consist of five H-
Bridges inverters. IGBT power electronic devices use as
the switching components. Hence in this CHMLI consist
twenty IGBT with similar type, and five separated DC
sources with equal amplitude. Input signals that
entrance to NN have to normalized, and for output signal
that exit from NN have to denormalized. Amount layers
and neurons in the each layer determined by
optimization, where the optimum condition occurs if the
NN system has little amount of neuron but have lowest
error rate.
The implementation of the feed forward neural network
based SPWM is interesting. The design of the feed
forward neural network proposed in this work consists
of three layers. The neural network used has one input
neuron. The feed forward neural network accepts
reference signal as input. Here we have twenty hidden
neurons which have to be tested and feed forward
neural network has tansigmoid characteristics. And the
neural network has five output neurons which gives
pulses as output the pulses which are generated are
given to CHMLI [7].

Fig -2: Five-level cascaded H-bridge multilevel inverter simulink model using SPWM
0 50 100 150 200 250 300 350 400 450 500
-10
-5
0
5
10
Time[ms]
Voltage[V]
Fig -3: Five-level CHMLI output voltaget waveform

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
-3
-2
-1
0
1
2
3
Time [us]
Current[A]
Fig -4: Five-level CHMLI output current waveform
0 500 1000 1500 2000
0
0.1
0.2
0.3
0.4
0.5
Frequency (Hz)
Fundamental (50Hz) = 9.076 , THD= 9.54%
Mag(%ofFundamental)
Fig -5: THD Spectrum of Five-level CHMLI output Voltage waveform
0 500 1000 1500 2000
0
0.1
0.2
0.3
0.4
0.5
Frequency (Hz)
Mag(%ofFundamental)
Fig -6: THD Spectrum of Five-level CHMLI output Current waveform

Fig -7: Block diagram of neural network controlled multilevel inverter
Fig -8: Five-level CMHLI using NN controller operating at Vdc= 2V

4.1 Five-level Cascaded H-bridge Multilevel
Inverter using NN Controller
The five-level CHMLI using NN controller
simulation model circuit diagram is developed as shown
in Figure 8 and the inverter is operated with Vdc = 2V.
CHMLI consist of five H-Bridges inverters circuit
as shown in Figure 8 uses IGBT power electronic device
as the switching components. Hence in this CHMLI
consist twenty IGBTs with similar type, and five
separated DC sources with equal amplitude. Input
signals to Neural Network have to be normalized, and
output signal of Neural Network have to be
denormalized. Total Amount of layers and neurons in the
each layer determined by optimization, where the
optimum condition occurs if the NN systems have little
amount of neurons but have lowest error rate. The NN
controller trained by their inputs. The output pulse
signals which are generated from this neural network
are given to CHMLI. Performance of training process in
the graph format is shown in Figure 9. This figure
indicate that training have small error.
Fig -9: Performance of training process
0 50 100 150 200 250 300 350 400
-10
-5
0
5
10
Time [ms]
Voltage[V]
Fig -10: Output voltage waveform of five level CHMLI using NN controller

0 200 400 600 800 1000 1200 1400 1600 1800 2000
0
0.1
0.2
0.3
0.4
0.5
Frequency (Hz)
Mag
Fig -11: THD spectrum of voltage waveform of five level CMHLI using NN controller
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
-3
-2
-1
0
1
2
3
Time [us]
Current[A]
Fig -12 : Output current waveform of five level CHMLI using NN controller
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
0
0.1
0.2
0.3
0.4
0.5
Frequency (Hz)
Mag(%ofFundamental)
Fig -13: THD spectrum of current wave form of five level CHMLI using NN controller

5. RESULTS
The corresponding output responses of the circuit are shown in figures 10 and 12 and the THD
spectrum of voltage and current waveforms are 8.77% and 2.76% respectivly as shown in Figure11 and 13
0 200 400 600 800 1000 1200 1400 1600 1800 2000
0
0.1
0.2
0.3
0.4
0.5
Frequency (Hz)
Mag
Table -1: Comparison of THD of multilevel Inverters with and without NN controller
Five-level MLI Voltage THD in % Current THD in %
Conventional CHMLI 9.54 3.33
CHMLI using NN controller 8.77 2.76
THD of CHMLI using NN controller is further more decreased than the conventional five-level inverter.
Here comparison of the conventional and neural network based multilevel inverter performances by considering
the THD parameters is given in table 5.1.
From the comparison table it can conclude that neural network based multilevel inverter has better performance
than conventional multilevel inverters.
6. CONCLUSION
In this paper multilevel inverter using intelligent technique has been developed namely artificial neural networks is used
to realize the proposed technique. The multilevel inverters simulink models are developed using matlab software. The
three-phase five level diode clamped multilevel inverter is developed using sinusoidal pulse width modulation. Three
phase five-level cascaded multilevel inverter is developed using sinusoidal pulse width modulation and five-level cascaded
multilevel inverter using neural network controller are developed and there results are compared. The multilevel inverter
which uses neural network has better performance than conventional one. From the results it is observed as the level
increases THD is decreased. Five-level cascaded multilevel inverter which is using neural network controller results in
2.76% THD. Neural based MLI compared with conventional MLI gives betterperformance.
REFERENCES
[1] F.Z.Peng, J.S Lai, “Multilevel Converters”,IEEE Transactions on Industry Applications,Vol.32
No.3,May/June, pp.509-517.
[2] A. Nabae, I. Takahashi, H. Agaki, “A New Neutral-Point-Clamped PWM, Inverter,” IEEE Transactions on Industry
Applicaitions. Vol.IA-17, No.5, Sep / Oct, 1981, pp.518-523.
[3] P. M. Bhagwat and V. R. Stefanovic, “Generalized Structure of a Multilevel PWM Inverter,” IEEE Transactions on
Industry Applications, Vol.IA-19, No.6 Nov.Dec., 1983, pp.1057-1069.
[4] Mohammed H. Rashid. “Power Electronics” Prentice-Hall of India Private Limited, Second Edition, 1994(Book).
[5] Richard Lund “Multilevel power electronic converters for electrical motor drives” Doctoral thesis at NTNU
2005:62.Trondheim April 2005.pp 19.

[6] J. Rodriguez, S. Bernet, B. Wu, J. Pontt and S. Kouro, “Multilevel voltage-source-converter topologies for industrial
medium-voltage drives,” IEEE Trans. Ind. Electron., vol. 54, no. 6, pp. 2930–2945, Dec.2007.
[7] Basil M. Saied , Qais M. Alias, “Intelligent Systems based Selective Harmonic Elimination (SHE) for Single Phase
Voltage source Inverter” University of Mosul Vol.16 No.3Aug.2008.

Development of Multilevel Inverters for Control Applications

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Development of Multilevel Inverters for Control Applications