International Journal of Electrical Engineering & Technology (IJEET) Volume 7, Issue 3, May–June, 2016, pp.117–125, Article ID: IJEET_07_03_010 Available online at http://iaeme.com/Home/issue/IJEET?Volume=7&Issue=3 ISSN Print: 0976-6545 and ISSN Online: 0976-6553 Journal Impact Factor (2016): 8.1891 (Calculated by GISI) www.jifactor.com © IAEME Publication
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://iaeme.com/Home/issue/IJEET?Volume=7&Issue=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 http://iaeme.com/Home/journal/IJEET 117 [email protected] 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 (T STC - 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) 2 TSTC[°C]=Temperature at Standard test conditions (25°C and 1000 W/m ) 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
http://iaeme.com/Home/journal/IJEET 118 [email protected] 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
http://iaeme.com/Home/journal/IJEET 119 [email protected] 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 % 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. http://iaeme.com/Home/journal/IJEET 120 [email protected] 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 http://iaeme.com/Home/journal/IJEET 121 [email protected] 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 http://iaeme.com/Home/journal/IJEET 122 [email protected] Fuzzy Logic Control Based Grid Integration Of Photovoltaic Power System Using 11 Level 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 REFERENCE [1] S. Ahmad, S. H. Johari, A. Ahmad and M. F. M. A. Halim, Grid connected multilevel inverters for PV application, 2015 IEEE Conference on Energy Conversion (CENCON), Johor Bahru, 2015, pp. 181–186. [2] M. R. Reddy and J. Chelladurai, PV fed grid connected multilevel inverter with space vector control having over modulation, Circuit, Power and Computing Technologies (ICCPCT), 2014 International Conference on, Nagercoil, 2014, pp. 516–522. [3] Q. Huang, M. Wang, W. Yu and A. Q. 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