International Journal of Electrical Engineering & Technology (IJEET)
Volume 7, Issue 3, May–June, 2016, pp.117–125, Article ID: IJEET_07_03_010
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ISSN Print: 0976-6545 and ISSN Online: 0976-6553
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FUZZY LOGIC CONTROL BASED GRID
INTEGRATION OF PHOTOVOLTAIC
POWER SYSTEM USING 11 LEVEL
CASCADED H-BRIDGE INVERTER
Divya Singh Chouhan, Maya Buliwal, Priyambada Shahi, Vikramaditya Dave
Electrical Dept., College of Technology and Engineering, India
ABSTRACT
This paper discourse about design and modeling of distributed
Photovoltaic power system using a 11 Level Cascaded H-Bridge Inverter for
the purpose of grid integration. The MOSFET switches helps in power quality
improvement by decreasing the Total Harmonic Distortion using multilevel
inverter. The proposed grid connected Power System has been designed and
analyzed in MATLAB Simulink environment. Fuzzy Logic based Intelligent
Controller has been implemented for voltage regulation at Point of Common
Coupling of Grid connected PV Power System. Obtained results from
Simulation model and compared with IEEE Standard 1547 for endorsing the
effectiveness of the proposed system.
Key words: PV Power System, CHB Inverter, Fuzzy Logic, Grid Integration
Cite this Article: Divya Singh Chouhan, Maya Buliwal, Priyambada Shahi
and Vikramaditya Dave, Fuzzy Logic Control Based Grid Integration f
Photovoltaic Power System Using 11 Level Cascaded H-Bridge Inverter.
International Journal of Electrical Engineering & Technology, 7(3), 2016, pp.
117–125.
http://www.iaeme.com/ijeet/issues.asp?JType=IJEET&VType=7&IType=3
1. INTRODUCTION
Energy crisis leading to energy demand across the globe force us to switch to other
sources of energy. Renewable Energy sources prefer more due to their less carbon
emission. In the countries of the equatorial region solar energy is abundant, so
Photovoltaic Power Systems are the commonly used renewable energy. Considering
various different cases, Multilevel Inverters play major role in the Power Quality
improvement in renewable energy power systems [1 - 4]. For maximum utilization
distributed power systems are the most suitable in photovoltaic power systems.
Cascaded H-Bridge type multilevel inverters are the appropriate one for the
distributed photovoltaic power system. Fuzzy logic based intelligent controller is used
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Divya Singh Chouhan, Maya Buliwal, Priyambada Shahi and Vikramaditya Dave
in continuous monitoring of the grid connected photovoltaic power system and
controlling the cascaded H-bridge inverter.[5] Block diagram representing the grid
connected photovoltaic power system is shown in figure 1.
Figure 1 Block Diagram of grid connected PV power system
2. PHOTOVOLTAIC ARRAY
Photovoltaic cells are devices capable of converting the energy from the sun into a
flow of electrons by Photovoltaic effect. Combinations of PV cells provide module
and several modules together form a Photovoltaic Array. The energy produced by the
Photovoltaic Array is unswerving reliant on the Temperature and Irradiation of the
sunlight [22]. Based on these the open circuit voltage can be calculated as follows,
VOC ambient = Temperature Coefficient (TSTC - Tambient + Voc rated )
Where
VOC ambient = Open circuit voltage at module temperature
Temperature Coefficient = 0.12 V/C
(When the temperature decreases by one degree Celsius the voltage increases by 0.12)
TST C[°C]=Temperature at Standard test conditions (25°C and 1000 W/m2 )
Tambient [°C]=Module Temperature
VOC rated = Open Circuit voltage at standard test conditions
The simulation of the photovoltaic array in MATLAB, Simulink is shown in
figure 2. An irradiation of 1000G and ambient temperature of 25˚C is provided as the
input for the solar array. From figure 3 the output voltage waveform of the solar array
shows that the array takes a time of 0.03secs to reach its rated output voltage is
88.3volts. Since a distributed photovoltaic power system is proposed eight separate
photovoltaic arrays have been used [3],[4].
Figure 2 Simulation of Photovoltaic Array
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Fuzzy Logic Control Based Grid Integration Of Photovoltaic Power System Using 11 Level
Cascaded H-Bridge Inverter
Figure 3 Output voltage waveform of Photovoltaic Array
3. CASCADED H-BRIDGE INVERTER
Generally Multilevel Inverters requires more number of components for increasing
the number of levels in the output level. Increasing the components leads to high loss.
Power quality of Renewable energy power system can be increased by reducing the
components used and increasing the output levels [6-10]. There are three Multilevel
Inverter topologies: Diode Clamped, Flying Capacitor and Cascaded H-bridge
inverter. Each topology has its own advantages and disadvantages [11-14]. Cascaded
H-Bridge inverters are the most suitable topology for a distributed photovoltaic power
system. These type inverters require comparatively less components than other
topologies for higher levels. Figure 4 shows MATLAB Simulation of the 11 level
cascaded H-bridge inverter. The inverter is connected to eight different photovoltaic
arrays for distributed generation. MOSFETs M1 to M20 connected to the solar arrays
form the DC-DC converter provides summed up boosted DC voltage from the
photovoltaic arrays. MOSFET 1 to MOSFET 4 forms the H-bridge inverter.
Figure 4 11 Level Cascaded H-Bridge inverter
The output voltage waveform of the DC-DC converter and H-bridge inverter are
shown figure 5 & 6. Total harmonic distortions are usually high in multilevel inverters
so filters are used to reduce the THD value.
Figure 5 Output waveform of DC-DC converter
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Divya Singh Chouhan, Maya Buliwal, Priyambada Shahi and Vikramaditya Dave
Figure 6 THD Output waveform of 11 level CHB inverter without fuzzy
Allowed amount of total harmonic distortion of distributed renewable according to
IEEE standard 1547 and IEC 61727 are show in the table 1.
TABLE 1 THD VALUES AS PER IEEE STANDARD 1547 AND IEC 61727
IEEE 1547 and IEC 61727
Individual
Harmonic order (odd)
H<11
11<h <17
17<h<23
23<h<35
35<h
THD (%)
%
4.0
2.0
1.5
0.6
0.3
5.0
4. INTELLIGENT CONTROLLER
In the standalone applications of photovoltaic power systems the required output is
always constant, so general embedded system based microcontrollers are used for the
purpose of controlling the inverters. During the grid connected applications the output
is continuously variable and is dependent on the load side so a closed loop system
with intelligent controller must be implemented for continuous monitoring of the grid
connected output and controlling the inverter accordingly [15- 19]. Various intelligent
controllers are Fuzzy Logic controllers, Bayesian controllers, Neural network
controllers, Hybrid (Neuro-fuzzy) controllers. For continuously variable output with
respect to fuzzy logic controllers are the recommended intelligent controller. The
simulation of fuzzy logic controller is performed in MATLAB using the FIS Editor
consisting of the Mamdani fuzzy inference system. Two input parameters, grid
voltage and PV inverter voltage sensed from the operating system are provided as
input to the controller. Fuzzification and defuzzification are performed by the rules
provided by means of the membership functions using the rule editor. The controller
itself generates the nominal operating surface required for generating the output. Here
the output is the gate pulse to be provided for the operation of MOSFET in the 11
level cascaded H-bridge inverter [18 - 22]. The controlling of MOSFET in the inverter
affects the output from the inverter so the photovoltaic power system is synchronized
with the grid.
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Fuzzy Logic Control Based Grid Integration Of Photovoltaic Power System Using 11 Level
Cascaded H-Bridge Inverter
Figure 7 11 Level Cascaded H-Bridge inverter with intelligent controller
Figure 8 11 Levels Cascaded H-Bridge inverter with intelligent controller
5. GRID INTEGRATION OF PV POWER SYSTEM
Major issue during grid integration of the distributed photovoltaic power system is the
PV mismatch error, i.e., unequal generation of voltage from each panel. It occurs due
to various different reasons such as climatic conditions, accumulation of dust over
panels and manufacturing errors. The structure of cascaded H-bridge inverter
discussed above is designed such way to operate both symmetrically and
asymmetrically so the PV mismatch error is eliminated [21]. There should not be any
voltage sag in the output from the photovoltaic power system [7]. The output voltage
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Divya Singh Chouhan, Maya Buliwal, Priyambada Shahi and Vikramaditya Dave
of the photovoltaic power system should not exceed the main grid voltage at any
cause [5]. The PV power system must not be energized when the main grid is not
operating. Point of common coupling voltage (PCC) must not vary greater or lesser
than 5% the grid voltage [20]. To achieve these continuous monitoring of the grid
voltage is required and controlling of the inverter is necessary which is performed by
the intelligent controller. Figure 7 shows the MATLAB simulation of intelligent
controller based grid connected photovoltaic power system. In the simulation of the
grid, a two area system supplied by a generator along with the necessary transmission
and distribution equipment is utilized for effective study of the stability of the system
and effectual operation of the intelligent controller.
Figure 9 11 Level Cascade H – Bridge Photovltaic Cell Inverter Output Voltage
Figure 10 Grid connected 11 Level Cascade H – Bridge Photovltaic Cell Inverter Output
Voltage
Figure 11 THD Output waveform of 11 level CHB inverter with fuzzy Controller
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Cascaded H-Bridge Inverter
6. CONCLUSION
Thus a distributed photovoltaic power system using a 11 level cascaded H-bridge
inverter has been designed with MATLAB Simulink environment. H - bridged
MOSFET count helped in dipping the total harmonic distortions and the switching
losses, thereby increasing the efficiency of the system. Fuzzy logic controller based
multilevel inverter generate only THD is 1.08% as shown in figure 11 then this value
is compared with without fuzzy system THD value 20.77% as shown in figure 6. The
proposed model simulation value is validated with IEEE standard 1547 and
IEC61727.
ACKNOWLEDGEMENTS
We would like to express my heartfelt gratitutde and regards to my research guide Dr.
Vikramaditya Dave, Asstt. Professor, Department of Electrical Engineering, for being
the corner stone of my research work. It was his incessant motivation and guidance
during periods of doubts and uncertainities that has helped me to carry on with this
research work
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