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چكيده انگليسي :

Improving Flyback Inverter for Photovoltaic Application Samaneh Sharifzadeh s sharifzadeh@ec iut ac ir 23 February 2012 Isfahan University of Technology Isfahan 84156 83111 Iran Department of electrical and computer engineeringDegree M Sc Language PersianMohammad Madani madani104@yahoo comEhsan Adib e adib@cc iut ac irAbstract In recent years applying renewable energy in order to produce the required energy has become moreurgent Photovoltaic PV cells among various sources of renewable energy are widely used due to directconversion of solar power to electrical energy Many kinds of inverter circuits and control schemes forphotovoltaic power generation systems are studied in literature From noise reduction and safety viewpoints the ability to ground and isolate the load from the renewable power sources is one of the most importantissues for designing and implementing the interface circuit A conventional photovoltaic system has powerlosses due to mismatch between the photovoltaic modules shadow issues and other obstacles that partiallycover the modules The AC module system is recognized as a useful method for resolving these problems The AC module is the integration of the inverter and PV module into one electrical device in which aDC AC grid connected inverter is used in each individual PV module and the inverter operates to providethe maximum power point for PV module Flyback inverter has been widely used in industrial products forlow power applications The power switch applied in yback inverter converter operates under hardswitching Thus the voltage across the active switch suffers from high voltage spike due to the transformerleakage inductance The high peak voltage results in the low efficiency and high switching losses Thus softswitching yback inverters were proposed to increase system efficiency and reduce the switching losses ofthe active switch In this thesis a new zero voltage switching pulse width modulated flyback DC AC inverteris presented This inverter has a simple auxiliary resonant circuit which reduces switching losses and EMI The soft switching is achieved without increasing the voltage current stress of the switches In the proposedZVS inverter the auxiliary circuit can be disabled at low output voltages The auxiliary resonant circuitincludes a resonant inductance and a resonant capacitance which provides ZVS condition for the main switchand ZCS condition for the auxiliary switch The proposed inverter is analyzed and simulation results arepresented to justify the theoretical analysis The resonant capacitor is applied to minimize the voltage spike atthe transformer primary side so the voltage stress of the primary switch can be decreased In a regularflyback converter or flyback inverter a voltage spike occurs due transformer leakage inductance whichresonates with switch output capacitance In the proposed inverter the energy of leakage inductance isabsorbed by the snubber capacitor and then this energy is recovered through the auxiliary switch Also theproposed inverter is compared with other soft switching flyback inverters and its advantages overconventional flyback inverters are discussed Furthermore interleaving technique is applied to the proposedinverter in order to increase its power handeling capability and to reduce the current ripple Also in theinterleaved circuit the size of passive elements the size of output filter and the EMI noise are reduced Atfirst the circuit with two auxiliary circuits was simulated however due to many elements applied in thecircuit the circuit was complicated Finally the inverter with only one auxiliary circuit is simulated Therefore the number of elements is reduced and the circuit is simplified Keywords Flyback Inverter ZVS Interleaved Flyback Inverter

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