International Journal of Communication and Computer Technologies
Volume 03 – No. 2 Issue: 06 June 2015
ISSN NUMBER : 2278-9723
DESIGN AND IMPLEMENTATION OF EFFICIENT MPPT FOR SOLAR
POWER GENERATION WITH SEVEN LEVEL INVERTER
1
2
J.Karthika, ME (PED), PG Student, Department of EEE, PGP College of Engineering and Technology
A.SenthamaraiKannan, Associate Professor, Department of EIE, PGP College of Engineering and Technology
ABSTRACT
Designing and Implementation of a new solar power
generation system, which is composed of a dc/dc power, MPPT
controller using Incremental Conductance Algorithm and a
seven-level inverter. The dc/dc power converter integrates a dc–
dc boost converter and a transformer to convert the output
voltage of the solar cell array into two independent voltage
sources with multiple relationships. This new seven-level
inverter is configured using a capacitor selection circuit and a
full-bridge power converter, connected in cascade. Number of
devices of the proposed seven-level inverter is fewer than that of
the conventional multi-level inverters.
The capacitor selection circuit converts the two output
voltage sources of dc–dc power converter into a three-level dc
voltage, and the full-bridge power converter further converts
this three-level dc voltage into a seven-level ac voltage. In this
way, the proposed solar power generation system generates a
sinusoidal output current that is in phase with the utility voltage
and is fed into the utility. The salient features of the proposed
seven-level inverter are that only six power electronic switches
are used, and only one power electronic switch is switched at
high frequency at any time.
I. INTRODUCTION
A cascade multilevel inverter is a power electronic
device built to synthesize a desired AC voltage from several
levels of DC voltages. Such inverters have been the subject
of research in the last several years, where the DC levels
were considered to be identical in that all of them were
batteries, solar cells, etc. In, a multilevel converter was
presented in which the two separate DC sources were the
secondary‟s of two transformers coupled to the utility AC
power. In contrast, in this paper, only one source is used
without the use of transformers. The interest here is
interfacing a single DC power source with a cascade
multilevel inverter where the other DC sources are
capacitors. Currently, each phase of a cascade multilevel
inverter requires n DC sources for 2n+1 levels in applications
that involve real power transfer In this work, a scheme is
proposed that allows the use of a single DC power source
(e.g., battery or fuel cell stack) with the remaining n - 1 DC
sources being capacitors. It is shown that one can
simultaneously maintain the DC voltage level of the
capacitors and choose a fundamental frequency switching
pattern to produce a nearly sinusoidal output.
II OPERATION AND DESIGN
The concept of utilizing multiple small voltage
levels to perform power conversion was patented by an MIT
researcher over twenty years ago. Advantages of this
multilevel approach include good power quality, good
electromagnetic compatibility (EMC), low switching losses,
and high voltage capability. The main disadvantages of this
technique are that a larger number of switching
semiconductors are required for lower-voltage systems and
the small voltage steps must be supplied on the dc side either
by a capacitor bank or isolated voltage sources. The first
topology introduced was the series H-bridge design . This
was followed by the diode clamped converter which utilized
a bank of series capacitors.
In this design, the semiconductors block the entire
dc voltage, but share the load current. Several combinational
designs have also emerged some involving cascading the
fundamental topologies. These designs can create higher
power quality for a given number of semiconductor devices
than the fundamental topologies alone due to a multiplying
effect of the number of levels. Recent advances in power
electronics have made the multilevel concept practical.
In fact, the concept is so advantageous that several
major drives manufacturers have obtained recent patents on
multilevel power converters and associated switching
techniques. Furthermore, several IEEE conferences now
hold entire sessions on multilevel power conversion. It is
evident that the multilevel concept will be a prominent choice
for power electronic systems in future years, especially for
medium-voltage operation.
III DC TO DC CONVERTER AND MPPT
The switching converters convert one level of
electrical voltage into another level by switching action. They
are popular because of their smaller size and efficiency
compared to the linear regulators. DC-DC converters have a
very large application area. These are electronic devices to
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DC distribution system has been considered as an
effective solution to Internet Data Centers (IDC) where
electronic loads which prefer dc-type power, account for
most of the energy consumption and battery-applied
Uninterruptible Power Supplies (UPS) are essential for
system reliability. In dc-interfaced IDC, the system efficiency
is improved streamlining the interfaces among the utility
source, dc loads and battery storage device. While ac gridconnected PV systems are well known due to their wide
application, the concept of the dc-interfaced PV systems
would be unfamiliar to the public.
EFFICIENCY
provide DC voltages. The wide variety of circuit topology
ranges from single transistor buck, boost and buck-boost
converters to complex configurations comprising two or four
devices and employing soft-switching or resonant techniques
to control the switching losses.
There are some different methods of classifying DCDC converters. One of them depends on the isolation
property of the primary and secondary portion. The isolation
is usually made by a transformer, which has a primary
portion at input side and a secondary at output side. Feedback
of the control loop is made by another smaller transformer or
optically by opto coupler. Therefore, output is electrically
isolated from input. However, in portable devices, since the
area to implement the bulky transformer and other off-chip
components is very big and costly, so non-isolation DC-DC
converters are more preferred.

Buck converter (step down DC-DC converter),

Boost converter (step up DC-DC converter),
COST

Buck-Boost converter (step
converter, opposite polarity),

Cuk converter (step up-down DC-DC converter).
The reduced number of power stages and
components, and availability of simple structure and control
would lead to cost reduction. In addition, maintenance cost
can also be reduced due to the improved reliability.
up-down DC-DC
BOOST CONVERTER
Depicts a step-up or a PWM boost converter. It is
comprised of DC input voltage source VS, boost inductor L,
controlled switch S, diode D, filter capacitor C, and load
resistance R. The converter waveforms in the CCM are
presented. When the switch S is in the ON state, the current
in the boost inductor increases linearly. The diode D is OFF
at the time. When the switch S is turned off, the energy
stored in the inductor is released through the diode to the
input RC circuit.
B.
RELIABILITY
Electrolytic capacitors are employed to decouple ac
side from PV side to guarantee high MPPT efficiency, but
their short lifetime heavily affects the reliability of a PV
generation system while the lifetime of PV panels
continuously.
Non-isolated DC/DC converters can be classified as follows:
A.
In addition to the streamlined power flow without
redundant stages, utilization of simple topologies and control
methods would additionally improve the conversion
efficiency. On the other hand, the ac counterpart requires
complicated structure and control for injecting sinusoidal
current. While the ac system requires PV power circuit be
designed for the peak instantaneous power, which is double
of average power, the dc PV system can be designed for the
rated power, which would also improve its conversion
efficiency. In addition, the elimination of ac fluctuation
reduces line frequency voltage ripple on PV side which can
contribute to achieving higher MPPT efficiency.
C.
CURRENT SENSOR-LESS BCM BOOST
CONVERTER
Various topologies can be utilized as a PV interface.
In this paper, a boost converter is selected for the interface
circuit due to its simplicity and high efficiency considering
the voltage and power rating of a BIPV module.
However, conventional boost converters in
Continuous Conduction Mode (CCM) suffer from high
voltage stress on its active switch and reverse recovery
problem of its diode.
DC DISTRIBUTION WITH PV GENERATIONS
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karthika and senthamaraikannan
To overcome these drawbacks, BCM is employed in
which Zero Voltage Switching (ZVS) can be achieved and
the diode reverse recovery problem is avoided by letting it
smoothly turn off at zero current.
analysis with the increasing attention to energy savings and
battery life in mobile devices, microprocessors and chipsets
integrate different functional blocks such as I/O, analog
circuits, memory, and graphics on the same die.
D.
For power efficiency, each block may operate at a
different DC supply voltage, resulting in multiple DC-DC
power converters on the same printed circuit board, which
occupy growing fraction of the board area. Integrated on-die
DC-DC converters may provide a solution for the PCB
resource issue, enabling a larger number of different on-chip
voltage supplies. Power efficiency is one of the most critical
parameters of on-chip DC-DC converters. These converters
require inductors which cannot be efficiently implemented on
die, but can be embedded inside the package. Typically, these
inductors have an air-core (no ferromagnetic materials are
used), and therefore exhibit a low inductance in the range of
few nH. A buck converter needs to operate at high switching
frequencies (hundreds of MHz) for the inductor to be
sufficiently small.
MATHEMATICAL ANALYSIS OF BCM
Voltage and current waveforms of the BCM boost
converter during a period are depicted in Fig. 5. It should be
noted that the third subinterval exists during which inductor
L and parasitic capacitor Cross of switch S resonate. This
negative current interval TR from T0 to T1 should be
considered for high reliability of current estimation especially
in light load conditions because it is independent of power
level. Considering this resonance interval, mathematical
analysis of the three operation modes is carried out and it is
utilized to estimate the PV current information in the
proposed algorithm.
E.
CONVERSION EFFICIENCY OPTIMIZATION
As the output power decreases, the converter
operates in QRM using valley skipping and low frequency
DCM to minimize the switching loss. As demonstrated in the
efficiency optimizer determines the operation mode. In
QRM, the ZCD signals are intentionally ignored and the
pulse width modulation (PWM) controller turns on the switch
at the next valley for high efficiency by achieving ZVS. In
DCM, the switching loss is further reduced by lowering the
switching frequency well below that of BCM.
To determine when the efficiency optimizer changes
the operation mode, loss analysis should be conducted for the
target application. Results of the loss analysis for the target
system specification and circuit parameters are well matched
with the previous discussions. The analysis considers
conduction, turn-on, and turn-off losses of the switch,
conduction loss of the diode, and copper and core losses of
the magnetic inductor. No reverse recovery loss of diode is
included because soft turn-off of diode is achieved in the
entire operation range.
It is clear that BCM is the most efficient from
medium to high power range, QRM is efficient from 20 to 40
W, and low frequency DCM is effective from 0 to 20 W due
to the ZVS operation and the minimized switching loss. It is
assumed that the converter operates at 20 kHz in DCM to
prevent audible noise generation. The number of valley
skipping operations affects the efficiency of QRM as shown
in Fig. 8. However, it is fixed at 1 in the target system, as the
power range where QRM with n = 2 has higher efficiency
than that with n = 1, is covered by DCM according to the loss
IV. SOLAR PANEL
A solar panel (photovoltaic module or
photovoltaicpanel) is a packaged, interconnected assembly of
solar cells,also known as photovoltaic cells. The solar panel
can beused as a component of a larger photovoltaic system
togenerate and supply electricity in commercial and
residentialapplications.Because a single solar panel can
produce only a limitedamount of power, many installations
contain several panels.A photovoltaic system typically
includes an array of solarpanels, an inverter, and sometimes a
battery andinterconnection wiring.
V. MPPT CONTROL TECHNIQUE
The weather and load changes cause the operation
of a PV system to vary almost all the times. Adynamic
tracking technique is important to ensure maximum power is
obtained from thephotovoltaic arrays. The following methods
are the most fundamental MPPT Technique, andthey can be
developed using micro controllers.
The MPPT Technique operates based on the truth
that the derivative of the output power (P) withrespect to the
panel voltage (V) is equal to zero at the maximum power
point. In the literature,various MPP algorithms are available
in order to improve the performance of photovoltaic
systemby effectively tracking the MPP. However, most
widely used MPPT Techniqueare consideredhere, they are:
1. Perturb and Observe (P&O)
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Design and implementation of efficient MPPT for solar power generation with seven level inverter
2. Incremental Conductance (InCond)
3. Constant Voltage Method.
A. Perturb and Observe (P&O) Method
The most commonly used MPPT Technique is P&O
method. This Technique uses simple feedbackarrangement
and little measured parameters. In this approach, the module
voltage is periodicallygiven a perturbation and the
corresponding output power is compared with that at the
previous perturbing cycle. In this algorithm a slight
perturbation is introduce to the system. Thisperturbation
causes the power of the solar module various. If the power
increases due to theperturbation then the perturbation is
continued in the same direction. After the peak power
isreached the power at the MPP is zero and next instant
decreases and hence after that theperturbation reverses as
shown in Figure 3.1.
When the stable condition is arrived the algorithm
oscillates around the peak power point. Inorder to maintain
the power variation small the perturbation size is remain very
small. Thetechnique is advanced in such a style that it sets a
reference voltage of the module correspondingto the peak
voltage of the module. A PI controller then acts to transfer
the operating point of themodule to that particular voltage
level and this technique is very popular and simple.
When the optimum operating point in the P-V plane
is to the right of the MPP, we have (dIPv/dvPv)+(IPV/VPV)<0,
whereas when the optimum operating point is to the left of
the MPP, we have (dIpv/dVpv)+(Ipv/Vpv)>0.
The MPP can thus be tracked by comparing the
instantaneous conductance Ipv/Vpvto the incremental
conductance dIpv/dVpv. Therefore the sign of the quantity
(dIpv/dVpv)+(Ipv/Vpv) indicates the correct direction of
perturbation leading to the MPP. Once MPP has been
reached, the operation of PV array is maintained at this point
and the perturbation stopped unless a change in dIpvis noted.
In this case, the algorithm decrements or increments Vrefto
track the new MPP. The increment size determines how fast
the Maximum power point is tracked.
Through the IC algorithm it is therefore theoretically
possible to know when the MPP has been reached, and thus
when the perturbation can be stopped. The IC method offers
good performance under rapidly changing atmospheric
conditions. There are two main different IC methods
available in the literature. The classic IC algorithm (ICa)
requires the same measurements shown in Fig.10, in order to
determine the perturbation direction a measurement of the
voltage Vpvand a measurement of the current Ipv.
The Two-Model MPPT Control (ICb) algorithm
combines the CV and the ICa methods: if the irradiation is
lower than 30% of the nominal irradiance level the CV
method is used, other way the ICa method is adopted.
Therefore this method requires the additional measurement of
solar irradiation S as shown in Fig.3.2
Figure 3.2.Block Diagram of Incremental
Conductance Algorithm
Figure 3.1. Graph Power versus Voltage for Perturb and
Observe Algorithm
B. Incremental Conductance Method
The Incremental Conductance (IC) algorithm is
based on the observation that the following equation holds at
the MPP.
[dIPV/dVPV] + [IPV/VPV]=0(1)
VI. BLOCK DIAGRAM OF PROPOSED SYSTEM
whereIPVand VPVare the PV array current and voltage,
respectively.
Volume 03 – No.2 Issue: 06
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theproposed solar power generation system generates a
sinusoidaloutput current that is in phase with the utility
voltage and is fedinto the utility, which produces a unity
power factor. As canbe seen, this new seven-level inverter
contains only six powerelectronic switches, so the power
circuit is simplified.
A. OUTPUT CHARACTERISTICS
Figure.6.1 Proposed Block diagram of the seven level
H-Bridge
S.No
Output
Voltage
ON switches
OFFswithces
Levels
1
2
3
4
5
S1,S2
S1,S2
S1,S2
S1,S2
S3,S4
S3,S4
S3,S4
S3,S4
S3,S4
S1,S2
+3Vdc
+2Vdc
+1Vdc
0
-1Vdc
6
S3,S4
S1,S2
-2Vdc
7
S3,S4
S1,S2
-3Vdc
Seven level inverter with new MPPT Technique
Figure.6.1shows the configuration of the proposed
solar power generation system. The proposed solar power
generation system is composed of a solar cell array, a dc–dc
power converter, anda new seven-level inverter. The solar
cell array is connected to the dc–dc power converter, and the
dc–dc power converter is a boost converter that incorporates
a transformer with a turn ratioof 2:1. The dc–dc power
converter converts the output power of the solar cell array
into two independent voltage sources with multiple
relationships, which are supplied to the seven-level inverter.
This new seven-level inverter is composed of a capacitor
selection circuit and a full-bridge power converter, connected
in a cascade. The power electronic switches of capacitor
selection circuit determine the discharge of the two
capacitors whilethe two capacitors are being discharged
individually or in series.Because of the multiple relationships
between the voltagesof the dc capacitors, the capacitor
selection circuit outputs athree-level dc voltage.
The full-bridge power converter furtherconverts
this three-level dc voltage to a seven-level ac voltagethat is
synchronized with the utility voltage. In this way,
Figure 6.4 Seven-level output phase voltage and each HbridgeOutput voltage.
B.
PERFORMANCE COMPARISON
Table 6.1 Performance comparison of Proposed system
with Existing system
VII. CONCLUSION
Design of an efficient solar power generation
system which converts the dc energy generated by a solar cell
array efficiently into ac energy that is fed into the utility is
obtained. The proposed solar power generation system is
composed of a dc–dc power converter and a seven level
inverter with Incremental Conductance MPPT. For nonvarying conditions, the two algorithms performed similarly,
Converters
Efficiency
Existing
Proposed
Input
Output
Input
output
Power in Watts 30.199
24.583
30.199
25.5424
230
201.5
230
208.8
0.1313
0.1120
0.1313
0.1228
Voltage in
Volts
Current in
Amps
Efficiency
81.15 %
84.58%
and both oscillated around the MPP. The incremental
conductance method has a slight advantage, and could
potentially oscillate lightly less due to turning around quicker
once passing the MPP. This reduces the switching power loss
and improves the power efficiency. The voltages of the two
Volume 03 – No.2 Issue: 06
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karthika and senthamaraikannan
dc capacitors in the proposed seven-level inverter
are balanced automatically, so the control circuit is
simplified. And concluding that the Incremental conductance
method has high power generation compare to perturb and
observer method which result in higher efficiency.
VIII. FUTURE ENHANCEMENT
The system can be extended for more voltage range
by increasing the step level. Increase in more voltage range
will increases the voltage gain and efficiency of the Proposed
system. When voltage and Current range increases
automatically Efficiency of the circuit also increases.
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