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چكيده انگليسي :

93 Investigation Improvement and Losses Reduction of Bridgeless Power Factor Correction Converters Farzad Hosseinabadi F Hosseinabadi@ec iut ac ir Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Degree M Sc Language PersianSupervisor Dr Ehsan Adib E Adib@cc iut ac ir Adviser Dr Hosein Farzanehfard Hosein@cc iut ac ir Abstract Today the incredible growth in the use of electronic devices that require DC powersupplies leads to employing more and more rectifiers Since diode rectifiers include diodesand capacitor DC power supplies draw nonsinusoidal current from power line and polluteline current by harmonic components Therefore power factor PF decreases and totalharmonic distortion THD increases Also Harmonics in power systems causeoverheating in transformers and induction motors and electromagnetic interference Inorder to minimize the power grid damages resulted by injected harmonics and achieve highpower factor in electrical equipment standards such as IEC61000 3 2 should be met Thus researchers have focused on improving power factor correction PFC topologies Theboost converter is widely used as a PFC converter due to its high PF and simplicity However boost converter cannot provide low output voltage Thus due to inrush currentproblem and the required low output voltage in some applications such as server telecommunication storage systems and networking the researchers have introduced bucktype PFC converter In bridgeless technique input bridge diode and PFC stages are mergedtogether to reduce the number of simultaneously conducting semiconductor devices In thisthesis two bridgeless buck PFCs are introduced The main drawback in the buck type PFCsis existence of dead angle when the output voltage is higher than input voltage which leadsto high current distortion and low PF Therefore in the first proposed PFC an auxiliaryswitch and in the second proposed PFC a Flyback converter are employed to omit deadangle from input current and improve PF All of two proposed PFCs operate under DCMcondition and shape input current inherently Due to elimination diode bridge theminimum number of semiconductor devises is applied in the power flow path thatdecreases conduction losses Furthermore all semiconductors turn on and off under softswitching condition Laboratory prototypes of the proposed bridgeless PFCs are designedand implemented to verify validity of theoretical analysis It is concluded that proposedbridgeless PFCs omit dead angle of input current and reduce THD Also due to reductionof the number of semiconductors in the power flow path and providing soft switchingcondition for semiconductors efficiency of proposed bridgeless PFCs are high and equal to 92 Key words Bridgeless Buck PFC Dead Angle Soft Switching

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بررسي، بهبود و كاهش تلفات مبدل‌هاي اصلاح ضريب توان بدون پل

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