Real Time Simulation of Solar Powered Cascaded Multilevel Inverter

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ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
Real Time Simulation of Solar Powered
Cascaded Multilevel Inverter
Shimi S.L, Dr. Thilak Thakur, Dr. Jagadeesh, Dr.S.Chatterji
Abstract— This paper deals with the design and simulation
of solar powered cascaded H-bridge multilevel inverter. The
Pulse Width Modulated (PWM) technique of switching pattern
is used to to improve the power quality of the supply voltage and
current and thus to reduce the Total Harmonic Distortion
(THD) . A detailed simulation has been carried out for the 11
level inverter and the validation of the system is verified
through MATLAB/SIMULINK and the results in terms of THD
are simulated.
Index Terms—Total Harmonic Distortion (THD), Solar
Powered Multilevel Inverter.
problem. The methods to solve such polynomial equations
using elimination theory are discussed in [8]. The solar
powered multilevel inverter introduces a lot of harmonics.
In this paper a PWM algorithm is used for the elimination
the higher order harmonics. To eliminate the low order
harmonics like 5th, 7th, 11th and 13th the fundamental
frequency switching scheme can be used. The knowledge of
harmonic elimination for multilevel inverter is very
necessary as it gives an idea about the switching pattern for
harmonic elimination in case of 11 level cascade multilevel
inverter [9].
II. MULTILEVEL INVERTER DRIVES (MLIDS)
I. INTRODUCTION
The industry has begun to stipulate higher power ratings.
The medium voltage applications require medium voltage
and megawatt power level. The solution for such an
application is the multilevel power converter structure. The
investigators in [1] have discussed the two topologies of
multilevel inverters for electric drive application. The high
VA rating of cascade multilevel inverter makes it fit for
large automotive electric drives and it uses several dc
voltage sources which would be available from batteries or
fuel cells [2]. One of the advantage of multilevel inverter is
that it enables the interface of renewable energy sources
such as photovoltaic, wind, and fuel cells in the dc
input portion of the multilevel inverter and can be used for
a high power application [1, 2]. Multilevel converters have
received more and more attention because of their
capability of high voltage operation, high efficiency, and
low electromagnetic interference (EMI) [3][1]. The
multilevel inverters use large number of power
semiconductor devices for their switching thus results in
more switching losses and is less reliable. But the
industrial applications such as industrial manufacturing are
more dependent on induction motors and their inverter
systems for process control. The IEEE 519 standard limits
of THD of the output voltage of the converter circuit should
be maintained for such applications [4]. In industries the
harmonics mitigation of multilevel inverter circuit is a very
important issue. In [5-7] the investigators have proposed
the elimination theory to determine the switching patterns
to eliminate the specific harmonics, such as 5th, 7th, 11th,
and the 13th. In case of 3 phase 11 level multilevel inverter
there are 15 dc sources, as the number of dc sources
increases the degrees of the polynomials in these equations
increases and thus it becomes difficult to solve such a
In industrial drives the conventional inverter drives are
most commonly used. They consist of six power switches
with pulse width modulation (PWM) switching. By using
such conventional converters the output voltage and current
waveform qualities has deteriorated. To overcome this
problem and improve the waveform quality the switching
frequency should be increased, but these results in higher
switching losses. Compared to the conventional two level
inverters the multilevel inverters have a number of
advantages from which some of them are listed below.
(i) As the number of levels of multilevel inverter is
increased the output staircase waveform is more
close to a sine wave thus very low distortion is
produced in the output.
(ii)
The dv/dt stress is reduced.
(iii) The stress in the motor bearings connected to a
multilevel motor drive is small as the commonmode (CM) voltage produced in the multilevel
inverters is very small. [10]
(iv) Low distortion input current.
(v) Multilevel inverter can work at both low and high
switching frequencies.
The investigator of [1] has mainly discussed two topologies
of multilevel inverters for electric drive application [1].
(a) The cascade MLID
(b) The back-to-back diode-clamped converter
The cascaded MLID is the main focus of this paper. The
Fig. 1 shows the single-phase structure of a m-level
cascaded inverter.
179
……(1)
ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
Rs
I
+
Rs
V
H
_
Fig. 2 Single Diode Model of a PV Cell
In literature a number of approaches and models can be
found to analyze the behavior of PVs [12-14]. The PV cell
model used in this work is based on the single diode cell .
The VI characteristics (in green) of a typical solar cell are
as shown in the
3 Fig. 3.
1
. PMPP
14
.
21
Cell current in A
IMP
P
MP
P
2
.
25
1
.
5
1
0
.
05
Cell voltage in V
V
oc
0
.
80
.
60
.
40
.
20
0
0
0
0
0
0
0
0
.
.
.
.
.
.
.
1
2
3 Curve
4 of 5Photovoltaic
6
7 Cell
Fig. 3 V-I and P-V Characteristics
When the voltage and the current characteristics are
multiplied we get the P-V characteristics (in blue) as shown
in Fig. 4. The point highlighted as MPP is the point at
which the panel power output is maximum [15]. The
equation (2) is the basic equation for the photovoltaic
current.
Fig. 1 Single-Phase Structure of a M-Level Cascaded
Inverter
III. PV MODELING
Modeling of a solar cell is done by connecting a current
source in parallel with an inverted diode along with a series
and a parallel resistance as shown in Fig.2. The series
resistance is due to hindrance in the path of flow of
electrons from n to p junction and parallel resistance is due
to the leakage current. The single diode model shown in
Fig. 2 [11] was adopted for simulating the PV module
under different irradiance and temperature levels. The
modeling of the PV cell was done in MATLAB/SIMULINK
by writing the code in the embedded block. The PV cell
subsystems were modeled and connected to the 11 level
cascade multilevel inverter.
…………………(2)
Where,
Ipv : photovoltaic current
I0 : saturation current
Vt : thermal voltage
Rs : equivalent series resistance
Rp : equivalent parallel resistance
a: diode ideality constant
IV. PROPOSED DESIGN
In this proposed method of the solar powered 11 level
cascade inverter, has five input stages, all the five stages are
alike in the construction module. All the modules are
180
Cell power in W
.
3
5
ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
connected as new hybrid with each module having power the FFT analysis tool and is shown in Fig.6 . The total
switches. The IGBT, MOSFET or any other power devices harmonic distortion is found to be 8.50 %.
can be used as the power switches in these modules. The
GTO’s are used in this system.
Fig. 5. Inverter Output Voltage
Fig. 4. Three-Phase Wye-Connection Structure for Solar
Powered 11 Level Cascade Inverter
In the switching mode of the power switches any two
switches are in operating conditions at a time and the other
two power switches remain in open condition. To attain
+Va, the switches S1 and S4 of Fig. 4 are turned on,
whereas to attain -Va switches S2 and S3 are turned on. If
power switches S1 and S2 or S3 and S4 are on , the output
voltage is 0, this method is adopted to protect the circuit
from short circuiting . Each H bridge module is connected
with a PV cell as shown in Fig. 4.
V. SIMULATED CIRCUITS AND WAVEFORMS
Figure 7. Shows the MATLAB/SIMULINK diagram of
the proposed three-phase wye-connection structure for solar
powered 11 level cascade multilevel inverter fed induction
motor. The subsystem of the solar powered 11 level cascade
multilevel inverter is shown in Fig 8. The Inverter’s phase
voltage and line voltage during simulation are shown in
Fig. 5. The FFT spectrum of the line voltage is found using
Fig. 6. FFT Spectrum
181
ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
Fig 7 Simulation Diagram Of Proposed System
Fig 8. Subsystem of the Solar Powered 11 Level Cascades Multilevel Inverter
VIII. CONCLUSION
A three-phase solar powered 11 level cascade inverter
has been proposed, and its principle of operation has been
conīŦrmed by simulation results. The PV cell modeling was
performed and the dc supply for all the H-bridges were
supplied through the PV cells. PWM switching pattern is
used to fire the GTOs of multilevel inverter for reducing the
Total Harmonic Distortion (THD) and to improve the
power quality of the supply voltage and current. The total
harmonic distortion is found to be 8.50 % for the proposed
model. Using the optimization and artificial intelligent
techniques and fractional order controllers in this proposed
model the THD can still be minimized.
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ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
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