A T-TYPE ISOLATED ZERO VOLTAGE SWITCHING DC-DC CONVERTER WITH CAPACITIVE OUTPUT

 

Abstract

A novel isolated dc-dc converter is proposed, usingthe T-Type topology with zero voltage switching and pulse widthmodulated(TT-ZVS-PWM) with a capacitive output filter. It usesfour switches, two of which are subjected to the input voltage,and the other two to half the input voltage. All switches commutateunder zero-voltage over a wide load range. The proposedconverter has the following features: (a) symmetrical operationof the isolation transformer, (b) modulation by pulse width withconstant frequency, (c) zero voltage switching, and (d) threelevelvoltage applied to the primary winding of the transformer.Theoretical analysis, design example, and experimental data fora 2 kW, 400 VDC input, 400 VDC output, and 50 kHz switchingfrequency laboratory prototype, working in two operating pointsare included in the paper. The measured efficiency was 95% at950W.

EXISTING  SYSTEM:

The full-bridge zero voltage switching modulated by pulsewidth with phase shift dc-dc converter(FB-ZVS-PWM-PS)is suitable for such applications due to the following features:high power density, zero voltage switching, bidirectionalpower transfer capability, modular, symmetric structure, andhigh-frequency galvanic isolation.The three-level zero voltage switching modulated with pulsewidth dc-dc converter(TL-ZVS-PWM) is used for high powerand high input voltages because it enables the use of lowvoltage rated semiconductor devices that has small on-stateresistance, small parasitic capacitance, reduced reverse recoveryof the intrinsic diode of MOSFETs, when compared tohigher voltage rated devices .It can be seen that both FB-ZVS-PWM-PS and TL-ZVSPWMshare similar features, but the rated DC-bus voltagedefines which one should be used. These features lead tohigh efficiency power conversion and generation of many othertopologies, starting from these two cells and improving someissues, such as ZVS over a restrict load range, reactive powercirculation and others.

PROPOSED  SYSTEM:

In order to overcome the issues of the HB-ZVS-PWM andimprove the primary winding voltage to a three level one, theT-type structure, recently proposed and successfully tested insingle and three-phase inverters, can be used .The aim of this work is to investigate the utilization of theT-type structure in the design of isolated dc-dc converters. Itwill be demonstrated that the proposed converter has featuressimilar to the FB-ZVS-PWM-PS and TL-ZVS-PWM converters,such as: operation at constant switching frequency, softswitching(ZVS) and symmetrical operation of the isolationtransformer. However, while the voltages across two powerswitches are equal to the DC bus voltage, two other switchesare subjected to half the input voltage, which allows theutilization of lower voltage switches. To improve the ZVSload range of the circuit, a small inductance is added in orderto improve the load range to a full range, improving theefficiency. Moreover, to overcome the reverse recovery issuein the secondary winding rectifier diodes, a capacitive filterclamps its voltages, also it imposes a linear rate of change inthe primary inductor currents. The commutation of the rectifierdiodes occurs with zero current, thus improving the efficiencyof the converter.

CONCLUSION

A new four-switch power-circuit topology, for realizationof isolated dc-dc converters with capacitive output filter wasproposed, analyzed, designed, and tested in the laboratory.From the theoretical and experimental results presented inthis paper, the proposed topology is well-suited to economicalrealization of high power density and high efficiency powersupplies

 

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