Design of Solar Power Generation System using Nine level Inverter
1
Aiyasamy V, 2Sathis Kumar M
1
M.E. Student of P.A. College of Engineering and Technology, Pollachi, aiyasamyv@gmail.com
2
HOD, Dept of PG-Electrical Science, P.A.College of Engineering and Technology, Pollachi.
Abstract— This paper generates a solar photovoltaic system with
dc-dc power converter and a nine level inverter, the nine level
inverter topology consists of less number of switches when
compared to conventional cascaded H bridge inverter the output
of solar PV panel system will be fed to a MPPT algorithm to
fetch a maximum amount of power from a photo voltaic system.
The P&O algorithm is used in MPPT technique for residential
renewable energy generation the output voltage of a solar PV
system is steeped up by use of dc-dc power converter. The nine
level inverter with reduced switches and a dc-dc power converter
with independent voltage sources for a inverter is used to reduce
harmonics generated from inverter. The harmonic reduction is
achieved by selecting appropriate switching angles. The proposed
method is implemented using MATLAB/SIMULINK.
However, they have the drawback of the required large
number of switching devices which equals 2(k-1) where k is
the number of levels. This number is quite high and may
increase the circuit complexity, and reduce its reliability and
efficiency. [2-5]
II. BLOCK DIAGRAM
Keywords: Photovoltaic, dc/dc power converter, inverter.
I. INTRODUCTION
Solar energy is becoming more important than fuel energy
because it produces less pollution and the cost of fuel energy
is rising, while the cost of solar arrays is decreasing. In smallcapacity distributed power generation systems using solar
energy may be widely used in residential applications in the
near future[1-2] Solar energy power conversion in grid
connected solar power generation system it converts dc power
by solar cell array into ac power and feed ac power in utility
grid .Inverter is necessary to convert the dc power to ac power
output of solar cell is low a dc-dc power converter is used in a
small capacity solar power system to boost the output voltage.
The three level converters was the first multi level inverter
introduced. A multilevel converter is a power electronic
system that synthesizes a desired output voltage from several
levels of dc voltages as inputs. With an increasing number of
dc voltage sources, the converter output voltage waveform
approaches a nearly sinusoidal waveform while using a
fundamental frequency-switching scheme.
The primary advantage of multi level inverter is their small
output voltage, results in higher output quality, lower
harmonic component, better electromagnetic computability,
and lower switching losses. While many different multilevel
inverter topologies have been proposed, the two most
common topologies are the cascaded H-bridge inverter and its
derivatives, and the Diode-clamped inverter. The main
advantage of both topologies is that the rating of the switching
devices is highly reduced to the rating of each cell.
Figure. 1. Block Diagram of Solar Power Generation System
Figure 1 shows the solar power generation system of
multilevel inverter. Its show the PV power module connected
to the dc-dc boost converter and MPPT is used to change the
duty ratio of the solar module. And then multilevel inverter to
convert the dc into requires ac sources to grid connected PV
system. [8]
III. STANDALONE PHOTOVOLTAIC SYSTEM COMPONENTS
A photovoltaic cell or photoelectric cell is a semiconductor
device that converts light to electrical energy by photovoltaic
effect. If the energy of photon of light is greater than the band
gap then the electron is emitted and the flow of electrons
creates current. However photovoltaic cell is different from a
photodiode. In a photodiode light falls on n channel of the
semiconductor junction and gets converted into current or
voltage signal but a photovoltaic cell is always forward
biased. Usually a number of PV modules are arranged in
series and parallel to meet the energy requirements. PV
modules of different sizes are commercially available
(generally sized from60W to 170W). For example, a typical
small scale desalination plant requires a few thousand watts of
power. A PV array consists of several photovoltaic cells in
series and parallel connections. Series connections are
responsible for increasing the voltage of the module whereas
the parallel connection is responsible for increasing the
current in the array. Typically a solar cell can be modelled by
a current source and an inverted diode connected in parallel to
it. It has its own series and parallel resistance. 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.[3-5]
Figure.3. Circuit Diagram of Boost Converter
Figure.2. Single Diode Model of a PV Cell.
In this model consider a current source (I) along with a
diode and series resistance (Rs). The shunt resistance (RSH)
in parallel is very high, has a negligible effect and can be
neglected. The output current from the photovoltaic array is
𝐼 = 𝐼𝑠𝑐 – 𝐼𝑑
𝑞𝑉𝑑
𝐼𝑑 = 𝐼𝑜 (𝑒 𝑘𝑇 − 1)
(1)
(2)
Where Io is the reverse saturation current of the diode, q is
the electron charge, Vd is the voltage across the diode, k is
Boltzmann constant (1.38 * 10-19 J/K) and T is the junction
temperature in Kelvin (K).
Figure .4. Mode 1 Operation of Boost Converter
When the switch is closed the inductor gets charged through
the battery and stores the energy. In this mode inductor
current rises (exponentially) but for simplicity we assume that
the charging and the discharging of the inductor are linear.
The diode blocks the current flowing and so the load current
remains constant which is being supplied due to the
discharging of the capacitor.
From equations. Simplify
𝐼 = 𝐼𝑠𝑐 – 𝐼𝑜 (𝑒
𝑞𝑉𝑑
𝑘𝑇
− 1)
(3)
Using suitable approximations,
𝐼 = 𝐼𝑠𝑐 – 𝐼𝑜 (𝑒 𝑞((𝑉 + 𝐼𝑅𝑠)/𝑛𝑘𝑇) − 1)
(4)
Where, I is the photovoltaic cell current, V is the PV cell
voltage, T is the temperature (in Kelvin) and n is the diode
ideality factor In order to model the solar panel accurately
using two diode model but in our project our scope of study is
limited to the single diode model.[5] Also, the shunt resistance
is very high and can be neglected during the course of our
study.
Figure.5. Mode 2 Operation of Boost Converter
In mode 2 the switch is open and so the diode becomes short
circuited. The energy stored in the inductor gets discharged
through opposite polarities which charge the capacitor. The
load current remains constant throughout the operation.
Output Current and Voltage Waveforms for A Boost
Converter. [5][7], [10-12]
IV. BOOST CONVERTER
The maximum power point tracking is basically a load
matching Problem. In order to change the input resistance of
the panel to match the load resistance (by Varying the duty
cycle), a DC to DC converter is required. It has been studied
that the efficiency of the DC to DC converter is maximum for
a buck converter, then for a buck-boost converter and
minimum for a boost converter but as we intend to use our
system either for tying to a grid or for a water pumping system
which requires 230 Vat the output end, so we use a boost
converter.
Figure.6.Output Current and Voltage Waveforms for A Boost
Converter
The simulation of solar PV cell with boost converter is shown
in figure
VI.
MULTILEVEL INVERTER
The multilevel inverters are used as voltage source inverters
(VSIs) in the static synchronous compensator (STATCOM), a
reactive power compensating device used for voltage
regulation in power systems.[9] There are mainly three types
of multilevel inverters, Diode- Clamped, Flying Capacitor and
Cascade Multilevel Inverter (CMLI). Among these three,
CMLI has a modular structure and requires least number of
components as compared to other two topologies, and as a
result, it is widely used for many applications in electrical
engineering. [12-15]To produce multilevel output ac voltage
using different levels of dc inputs, the semiconductor devices
must be switched on and off in such a way that the
fundamental voltage is obtained as desired along with the
elimination of certain number of higher order harmonics in
order to have least harmonic distortion in the ac output
voltage.[16-17] The proposed nine level inverter is simulated
using MAT LAB.
Figure.7.Simulation Diagram of Solar System and Boost
Converter
Figure.9.Simulation Diagram of nine level inverter
The output voltage waveform of solar PV cell and boost
converter are shown in
Figure.8. Solar Systems and Boost Converter Simulation
Result
The output voltage waveform of nine level inverter is shown
in the figure
Figure.10.Output Voltage Wave Form of Nine Level Inverter
TABLE 1 Comparison Of Different Multilevel Inverter Switches
Number of Switches
Inverter
Type
Cascaded
H Bridge
Proposed
method
%
Switching
Reduction
%
Harmonic
Reduction
5level
8
7level
12
9level
16
11level
20
6
8
10
12
25 %
33.3% 37.5% 40%
30.26 25.14
20.18
18.24
VII.
Conclusion
This paper proposes a solar power generation system to
convert the dc energy generated by a solar cell array into ac
energy that is fed into the utility. The proposed solar power
generation system is composed of a dc–dc power converter
and a nine level inverter. The nine-level inverter contains less
power electronic switches, which simplifies the circuit
configuration. This reduces the switching power loss and
improvesthepowerefficiency. Experimental results show that
the proposed solar power generation system generates a ninelevel output voltage and outputs a sinusoidal current that is in
phase with the utility voltage, yielding a power factor of unity.
In addition, the proposed solar power generation system can
effectively trace the maximum power of solar cell array.
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