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چكيده انگليسي :

Reducing Switching Losses in Current Fed Converters Mahdi Rezvanyvardom m rezvanyvardom@ec iut ac ir Date of Submission 2011 03 9 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Hosein Farzanehfard hosein@cc iut ac ir Abstract In recent years switching power supplies are widely employed in industry Thus improving the performance of DC DC converters is highly considered by researchers Generally switching converters are classified into two categories Voltage Source Converters VSC and Current Source Converters CSC Since some renewable systems such as fuel cells and solar cells have low output voltage which varies with output load thus converters with high voltage gain are required to increase the voltage level and provide regulation The main advantage of the current source converters is higher voltage gain than the voltage source converters Thus it is possible to use transformers with lower conversion ratio Another advantage of current source converters is the absence of output inductance in its structure Therefore these topologies are more cost effective when several output voltages are required Since most renewable systems cannot produce high peak currents therefore current source converters are preferred It is important to reduce the size and weight of switching power supplies Therefore power supplies at high switching frequencies are designed But higher switching frequencies would increase switching losses and reduces the circuit efficiency Therefore soft switching techniques are inevitable to reduce losses and increase switching frequency On the other hand the use of soft switching techniques is suitable solution to reduce RFI and EMI noise and get a better performance from semiconductor devices For high power applications series and parallel structures are important to reduce current stress and ripple In modern converters interleaved structures are considered for high current and high power applications due to advantages such as power distribution fast transient response smaller size of passive elements and current ripple In this thesis two new interleaved PWM Zero Current Switching ZCS boost converter are proposed to create soft switching conditions for all main and auxiliary switches The proposed converters use only one auxiliary switch to provide soft switching condition In order to reduce switching losses and to obtain a high efficiency a non dissipative soft switching cell is used In the proposed interleaved converter soft switching is obtained for all semiconductor devices The main and auxiliary switches turn on and off under zero current condition Also the reverse recovery losses of main diodes are reduced due to application of ZCS technique Implementation of control circuit is simple since the proposed circuit is controlled by pulse width modulation PWM method These converters have higher efficiency than the conventional PWM hard switching converter due to reduced switching losses Various operating modes of the two proposed converters the simulation results and the experimental results are presented Also the proposed converters are compared with similar existing converters and their advantages are justified The presented simulation and experimental results verify the theoretical analysis Finally the conclusions and recommendations for future research are expressed Keywords Current source converters Voltage source converter Interleaved boost converters Soft switching Zero current switching Zero voltage switching

رضواني وردوم، مهدي

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