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Fuzzy Based Transformer less Grid Connected PV System

N.Nandhini 1, R.Sathish Kumar2
  1. Department Of Electrical and Electronics Engineering, Anna University Regional office, Madurai, India
  2. Department Of Electrical and Electronics Engineering, Anna University Regional office, Madurai, India
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Abstract

In this paper fuzzy based three phase single stage trasformerless grid connected PV system is proposed. Due to the energy demand and GHG emission, renewable energy sources are become more popular. Nowadays renewable energy sources are mostly used in Distributed generation. Solar power generation system become more popular due to the suitability in distributed power generation .Three phase single stage current source inverter based trasformerless grid connected PV system uses a single converter unit (DC/AC CSI). Fuzzy based MPPT used for maximum power extraction from solar system. PR control technique used in voltage and current control loops. The three phase single stage grid connected PV system is simulated using MATLAB/SIMULINK and experimental result are presented

Keywords
Current Source Inverter (CSI), Maximum Power Point Tracking (MPPT), Proportional Resonant control, Green House Gas (GHG)

INTRODUCTION
A two stage grid connected PV system uses two conversion stage: First stage is DC to DC conversion (using chopper circuit) for boosting and conditioning and the second stage is DC to AC interfacing to the grid. This tow stage technique suffers from reduced efficiency higher cost and large size. In this proposed method the chopper circuit is eliminated, instead of the chopper circuit a double tuned resonant filter is used. The overall efficiency of the system is increased by a Maximum Power Point Tracking (MPPT) system is controlled by fuzzy logic controller.Using of voltage source inverter increase the necessity of using a bulky of transformer. In proposed method instead of voltage source inverter a current source inverter is used. A modified carrier based modulation technique is used in current source inverter. The current source inverter eliminates the transformer. The elimination of the transformer reduces the size of the system. The two stage grid connected PV system shown in fig.1 and single stage grid connected PV system shown in fig.2In conventional method the Voltage source inverter was commonly used due the simplicity and availability but the voltage source inverter requires bulky of transformer [1] and Maximum Power Tracking system used perturbing and observing algorithm. For harmonics reduction the system used a large inductive filter. More multilevel inverter have been used to improve the ac-side waveform quality and reduce the electrical stress on the power switches and reduce the power losses due to a high switching frequency [2][3] but the this merits are achieved at the expense of a more complex PV system. They used large and bulky transformer which increase the losses and reduce the system efficiency and also increase the cost of the system. The transformer is eliminated by replacing the voltage source inverter by current source inverter this method was discussed in [4] but this system used two stage converter circuit the chopper and inverter circuit. This system fails to implement the MPPT system. In [5] the efficiency of the system improved by MPPT system and current source inverter but the filter circuit not effective only LC filter was used. The single stage transformerless PV system explained in [6] it used MPPT system with hill clamping algorithm but this algorithm also not effective in changing weather condition. For harmonics reduction it used a low pass filter this give high THD level. The three-Phase CSI for PV Grid connected system was used in [7] successfully delivered PV power output to the grid, with a total harmonic distortion of 4.5. In [7] MPPT with perturbing and observing method was used and this system only used a current control loop.
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phase current source inverter based residential PV system was discussed this system used parallel resonant circuit on the dc side harmonics elimination. Various grid connected inverter circuit discussed in [14] .The inverters are categorized by the number of power processing stages and the type of power decoupling between the PV module and the grid. Power loss comparison between the single stage and two stage system discussed in [15]. The single stage system has lot of merits compare to two stage system. In single stage system has merits of saving of components and reducing cost. A fuzzy logic controller for maximum power point tracking system for photo voltaic system discussed in [16]. In [16] fuzzy logic based hill-climbing method used which offers fast and accurate converging to maximum operating point during steady-state and varying weather conditions. A multilevel inverter for photovoltaic system with fuzzy logic controller discussed in [17] used low pass filter for harmonic reduction it produce 2% of THD.A single phase single stage transformerless grid connected PV system discussed in [18] In this method only single phase system was discussed and the THD value is 1.5% In the followings section II explain about the system description; section III explain about solar PV system; section IV contain double tuned resonant filter; section V contain CPWM based CSI; Section VI deals the fuzzy logic controller and proportional resonant controller ; section VII discuss the simulation modeling and Result

SYSTEM DESCRIPTION
Three phase grid connected CSI shown in Fig .3. The inverter circuit has 6 MOSFET .A dc link inductor is used to connect the double tuned filter and the CSI.
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Fig. 3 Three phase grid connected current source inverter

SOLAR PV SYSTEM
Solar power generating system operating under principle of photo voltaic effect When the solar radiation fall on the PV cell the electrons in the atoms moves from
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Fuzzy Based Transformerless Grid Connected PV system

CONCLUSION
Fuzzy based three phase single stage grid connected PV system has been proposed. The harmonics are eliminated by the double tuned resonant filter. The power extracted from the PV array increased by the fuzzy based MPPT which develop the system performance in varying weather condition. The THD of the grid-injected current was 0.32 % and the THD level of the voltage is 0.72%.

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