برقراري شرايط سويچينگ نرم براي يك مبدل اصلاح ضريب توان ايزوله جديد و ارائه پيشنهاداتي به منظور عملكرد بهتر آنها

چكيده انگليسي :

Design of a New Isolated Soft Switching PFC with Imporved Performance Alireza Abasian Abasian alireza@yahoo com Date of Submission 2012 02 29 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Seyed Mohammad Madani madani104@yahoomail com Hosein Farzanehfard hosein@cc iut ac irAbstract Nowadays by ever increasing number of electronic devices the number of connected rectifiers to thenetworks is increasing constantly Because these rectifiers are non linear loads they produce current harmonicsand the input current shape is distorted compared to its ideal sinusoidal form This undesired harmonics causeproblems such as heating the motors and transformers increasing current flow in parallel capacitors and in theneutral wire in three phase four wire systems deforming the voltages shape and so on Thus different standardshave been imposed to restrict these harmonics To meet these standards a type of converter must be used in theinput stage of rectifiers to increase the power factor which is called power factor correction converter In thisthesis different types of power factor correction converters have been examined In general these converters aredivided into two groups of isolated and non isolated power factor correction converters In this group isolatedconverters converters with DC transformer are commonly used in low power applications because of theisolation between input and output the ability to have multiple outputs and also to increase the range of input tooutput voltage ratio Two stage power factor conversion converters are a general solution for improving thepower factor This type of converters have high power factor and fast output voltage response because of usingtwo separate controllers for each stage Main disadvantage of this type is its high cost because of its controlcircuits and power stages In order to reduce the cost the single stage converter idea is developed which mergethe PFC stage with a dc dc converter into one stage In most of them the PFC stage switch is replaced by someelements like auxiliary winding diode or passive components Hard switching of power switch of the rectifiercould make extra energy loss and therefore decreasing the efficiency of converter Thus with soft switching theefficiently can be increased and the switch loss could be minimized Some simple and basic topologies fromeach group are presented and analyzed Moreover problems advantages and disadvantages of each group aredescribed separately After analyzing these converters some solutions such as achieving soft switchingconditions reducing storage capacitor voltage and number of semiconductor elements on the power transitionpath to reduce the conductivity loss have been made to improve their performance The first proposed converter is a single stage single switch soft switching converter which is based on aboost flyback sheme In this converter soft switching condition is achieved without using any additional switch It also has fewer elements compared to similar converters Also a solution for improving the performance of thisconverter is presented The second proposed converter is improved quasi boost flyback converter In quasi boostconverter the boost switch is replaced with a magnetic switch combination of passive elements auxiliarywindings and diodes The proposed converter reduces the storage capacitor voltage and increases hold up timeof output voltage Furthermore the number of semiconductor elements in power transition path are reduced thusthe efficiency is improved Because of reducing the storage capacitor voltage and possibility of increasing itscapacity this converter is appropriate for specific applications such as computer and digital applications Operation principles of the proposed converters are fully analyzed and a prototype of each converter is realized Experimental data verify the theorical and simulation results Keywords 1 power factor

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