طراحي و ساخت مبدل چند سطحي فركانس محدود با مدار تعقيب كننده حداكثر توان جهت سيستمهاي انرژي خورشيدي متصل به شبكه

چكيده انگليسي :

104 Multi Level Inverter with Maximum Power Point Tracking Circuit for Grid Connected Photovoltaic Systems Ehsan Behrouzian e behrouzian@ec iut ac ir Date of Submission 2011 05 9 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language PersianSupervisor Ahmadreza Tabesh a tabesh@cc iut ac irAbstract This thesis deals with the design and implementation of power electronic interfaces for photovoltaicenergy systems with emphasis on suitable topologies for grid connected high power applications Photovoltaic PV solar cells are mainly semiconductor materials which directly convert solar energy intodirect current electricity Advances in solar cell technology steadily reduce the cost of photovoltaic energy inthe recent decades Currently small and medium power photovoltaic energy systems are commerciallyavailable and it has been predicted that photovoltaic energy system will be economically available in megawatt scales within the next few years Electrically PV energy systems are classified into stand alone and gridconnected systems Stand alone PV systems are often used in remote area and usually include electric energystorage Grid connected PV energy systems are often designed to inject generated electricity into a gridwithout using electric storage A power electronic interface is used in a PV energy system for two mainreasons i capturing maximum available power via adjusting the operating point of a PV cell so calledmaximum power point tracking MPPT algorithm and ii inverting the generated dc voltage to an ac voltagewith the desired frequency and voltage level for grid connected applications The thesis first reviews and compares existing MPPT algorithms and suggests a simple circuitry forrealization of one of these algorithms The suggested circuitry is designed based on fixed reference voltagemethod in which the operating voltage of PV cells will be fixed at an optimum voltage level regardless ofload variations The PV cell voltage is adjusted using a dc dc converter with a control system The suggestedcontrol circuitry is designed based on analog circuit approaches aiming to achieve maximum reliability Theproposed circuitry also includes a battery protection unit and its performance is experimentally evaluatedusing a PV test set up with four PV panels in different directions The simplicity of the proposed circuitryallows using it in a modular structure which in turn improves the reliability of the control system The thesis also investigates the grid connected PV energy systems and suggests a multi level invertertopology and control algorithm for high power PV system applications In this regard the existing grid connected topologies are investigated and their features are compared Then the multi level topology due toits capability in delivering power at medium voltage is introduced as a viable solution for high powerapplications The thesis proposes a 7 level converter topology with a limited frequency peak current controlapproach as a power electronic interface for grid connected PV energy systems In this control approach thegrid voltage is used as the reference of the injected current to the grid Therefore the power converter injectsthe solar energy with an almost unity power factor The circuitry is also used an MPPT method for capturingmaximum available power in PV solar cells The proposed circuitry and its control approach are validatedusing a PV system test setup and the performance of the circuitry is evaluated via harmonic analysis of themulti level converter output quantities Keywords Stand alone PV systems Grid connected PV systems Multilevel inverters Power factor correction Maximum power point tracking grid integration of PV energysystems

بهروزيان، احسان

طراحي و ساخت مبدل چند سطحي فركانس محدود با مدار تعقيب كننده حداكثر توان جهت سيستمهاي انرژي خورشيدي متصل به شبكه

تعقيب توان بهينه , ولتاژ مرجع ثابت , اصلاح ضريب توان , اينورترهاي چند سطحي , كنترل هيسترزيس , كنترل مدولاسيون دلتا