Implementation of Full-Bridge Current-Fed Resonant Boost Converter using PIC
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Implementation of Full-Bridge Current-Fed Resonant Boost Converter using PIC microcontroller
ABSTRACT

This paper presents a current-fed full-bridge boost DC-ACDCconverter with transformer isolation operating withoutswitching power dissipation. The output voltage is regulatedby dc-ac converter whose frequency changes with a constantturn-off time of transistors. The proposed converter is devoidof parasitic oscillations, as all of the parasitic capacitancesand inductances are included in a resonant tank circuit. Themain advantage of such systems is that they include acapacitive output filter, which is preferred in higher voltageapplications. Moreover, it achieves ZCS for all activeswitches and zero-voltage switching (ZVS) operation for alldiodes on high voltage side, which is an additional benefit. Inthis paper, the system operation is first explained, then amathematical description that is useful for its design isprovided, and finally, a report on the implementation of alaboratory prototype with 125W power is presented.Index terms-Bridge, current fed, boost, Dc-Dc converter, ZVS, ZCS.
1. INTRODUCTION
High voltage DC-AC-DC converters with an isolationtransformer are used in different types of electronicapplications such as battery chargers and dischargers,uninterruptible power systems, hybrid electric vehicles. Inthe case of the applications where low input voltages have tobe converted to high output voltages, current-fed convertersare used, whereas in the case of higher power applications,full bridge boost converters are usually a good choice.However, the design of high voltage dc-dc converters isproblematic because transformer parasitic elements canchange the converter behavior. The transformer leakageinductance causes undesirable voltage spikes that maydamage the circuit components, and the winding capacitancemay result in current spikes. A vital factor that determinesthe size and the cost of a converter is its operation frequency.In order to minimize the size and the cost, the frequency hasto be maximized. However, higher frequencies result in theincrease of transistor switching losses, and thus, theconverter’s effectiveness is limited. For that reason, manysolutions have been proposed to minimize converterswitching losses. The most popular control method of bridgeconverters is pulse width modulation (PWM). It utilizes aphase-shift control technique with constant frequencyoperation. The fixed frequency phase-shift control enablesthe implementation of ZCS for all converter switches.However, the switches must provide a reverse-voltageblocking capability. Thus, they have to be constructed bymeans of an MOSFET in series with reverse-voltageblocking diodes. The use of the diodes increases thecomponent count and cost, although it also causes higherconduction losses. Another solution proposed to minimizeconverter switching losses is a PWM boost full-bridgeconverter, in which the leading switches realize ZCS underwide load range, and the lagging switches realize zerovoltageswitching (ZVS) under any load. Likewise in thissolution, the leading switches have to be connected in serieswith reverse-voltage blocking diodes. In addition, acirculating current, which is a result of the introduction of anadditional auxiliary inductance (connected parallel with theprimary winding of the transformer), is the source of extraconduction losses.
2. EXISTING SYSTEM DESCRIPTION
The active clamp network serves to limit bridge switchturn-off voltage overshoot and enable the energy stored inthe transformer leakage inductance to be used for zerovoltageswitching. At switch turn-off that energyredistributes into the parasitic capacitance of the switches,causing a voltage overshoot capable of destroying devices.PWM phase-shift control of the bridge switches is utilized toobtain zero-current switching for two of the four bridgeswitches.
3. PROPOSED SYSTEMARCHITECTURE AND DESCRIPTION
The proposed converter system is devoid of parasiticoscillations as all the parasitic capacitances and inductancesare included in the resonant tank circuit. The characteristicfeature of resonant converters is that the transformerparasites do not disturb the circuit, because they are used asresonant circuit elements. In a current fed full bridge boostconverter type the overlapping conduction time of the fourconverter switches is kept constant and the output voltage isregulated by varying the switching frequency. Theconduction time is particularly calculated to ensure ZCSoperation under a wide load range. MOSFET’s and bodydiodes are used as the converter switches without the needfor any additional diodes in series. The converter transistorturn-off time is constant and is equal to the time of theparallel connected capacitor overcharge. During the ZCSswitch off-time, the L-C tank circuit resonates.


Download full report
http://ijcaonlinejournal/number7/pxc387283.pdf
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