بررسي و بهبود مبدل هاي با بهره ولتاژ بالا براي كاربردهاي فوتوولتائيك

چكيده انگليسي :

Analysis and Improvement of High Step Up Converters for Photovoltaic Applications Milad Heidari Khouzani mail milad heidari@ec iut ac ir Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan Iran Degree M Sc Language Farsi Supervisor Prof Hosein Farzanehfard hosein@cc iut ac ir Abstract Todays photovoltaic PV systems as popular renewable energy sources have gained numerous applications In thesesystems usually at first a DC DC converter is needed to increase the low level DC voltage of the PV panel less than 50V to the desired high level voltage 200V 400V suitable for connecting to DC bus voltage These DC DC converters areknown as high step up converters and in addition to PV systems they are needed in fuel cell systems uninterruptible powersupplies and hybrid electric vehicles The conventional boost converter as the simplest non isolated step up converter mustoperate at very high duty cycles to provide high conversion ratio which leads to low efficiency due to high conduction andswitching losses In addition high voltage stress across the converter switch and the output diode is another disadvantage ofthe boost converter Hence it is not suitable for mentioned applications In addition to limited voltage gain switching lossesand reverse recovery problem of the diodes are another problems in conventional boost converter which limit the converterswitching frequency and overall achievable efficiency In this thesis at first PV modules and photovoltaic systems areintroduced In chapter II different techniques for increasing the voltage gain of the converter are discussed Then a reviewof various high step up topologies is presented In Chapter III the first proposed converter is introduced In this chapter anovel step up converter with single switch single magnetic core and continuous input current is presented for photovoltaicapplications The proposed converter is obtained by integrating boost and Cuk converters so that only one switch and onemagnetic core is utilized to provide a high voltage gain This topology reduces voltage stress across the converter switch anddiodes and provides higher voltage gain compared with the basic Boost and Cuk converters Thus high quality and low voltage MOSFET at moderate duty cycles can be used to increase the converter efficiency In order to provide soft switchingcondition for the converter switch a soft switching auxiliary circuit as lossless passive snubber is added to the proposedconverter in chapter IV The auxiliary circuit provides soft switching condition at a wide range of output power In addition reverse recovery problem of the output diode is alleviated In chapter V an improved Quasi Z Source QZS converter ispresented The proposed converter utilizes a switched capacitor circuit to increase the voltage gain of the converter anddecrease the voltage stress of the components Moreover soft switching conditions are provided for the converter switchby using an active auxiliary circuit as zero voltage transition ZVT cell Soft switching conditions are obtained for theauxiliary switch too Hence very high voltage gain is achieved and the overall efficiency of the converter is increased aswell Furthermore the reverse recovery problem of all diodes is eliminated Operating principles of each proposed converterare analyzed and design considerations are provided In order to validate the theoretical analysis prototypes of the proposedconverters are implemented and the experimental results are exhibited Key Words Photovoltaic systems high step up converters soft switching

حيدري خوزاني، ميلاد

بررسي و بهبود مبدل هاي با بهره ولتاژ بالا براي كاربردهاي فوتوولتائيك

انرژي هاي تجديدپذير , سيستم هاي فوتوولتائيك , مبدل هاي DC-DC با بهره ولتاژ بالا , كليدزني نرم