A Fully Soft-Switched Multiphase DC-DC Converter with ... - IEEE Xplore

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Abstract- this paper proposes a fully soft-switched multiphase dc-de converter for high power application. The proposed multiphase converter exhibits low switch ...
The 2014 International Power Electronics Conference

A Fully Soft-Switched Multiphase DC-DC Converter with Reduced Switch Count for High Power Application Minjae Kim, Daeki Yang, Sewan Choi, IEEE Senior Member Department of Electrical and Information Engineering Seoul National University of Science and Technology Email: [email protected]

Abstract-

this paper proposes a fully soft-switched

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multiphase dc-de converter for high power application. The

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proposed multiphase converter exhibits low switch count

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and simple gate driver circuit. Owing to use of low rated lossless passive clamp and series resonant circuits, ZCS

turn-on and ZVS turn-off of switches and ZCS turn-off of

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diodes are achieved. Further, despite the passive clamp

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method, operating duty cycle range is not limited, resulting

Fig. I. Proposed multiphase converter

in no additional start-up circuitry required. Experimental results on a 50kHz, 5kW prototype are provided to validate the proposed converter.

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Keywords- Soft switching, high power dc-dc converter, muitiphase, lossless snubber

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INTRODUCTION

In the application such as fuel cell systems, distributed power generation, hybrid electric vehicles and photovoltaic systems the high power isolated boost dc-dc converter is required. The three-phase dc-dc converter can be used for the high power isolated boost dc-dc converter. They can be classified into voltage-fed and current-fed. The voltage-fed converter [1-2] suffers from high transformer turns ratio, leading to disadvantages associated with large leakage inductance. Compared to the voltage-fed topology, in general, the current-fed topology exhibits lower transformer turns ratio, smaller input current ripple and lower diode voltage rating. The three-phase current-fed topology has two types: passive clamping [3-4] and active clamping [5-8]. The three­ phase current-fed converter with passive clamp [3-4] has

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Fig. 2. Lossless snubber bank of the proposed multiphase converter

not have reverse recovery problem due to ZCS tum off of rectifier diodes. Further, unlike the current-fed converter with passive clamp, the whole duty cycle range between 0 and 1 can be used for the switch of the current­ fed converter with active clamp. However, a drawback of the current-fed converter with active clamp is to use more switches and gate driver circuits for them. In this paper, a fully soft switched multiphase converter is proposed for high power application. The proposed multiphase converter has the following features: 1) low switch count and simple gate driver circuit due to the switches with the common ground 2) low rated lossless passive clamp circuit, making it possible to achieve low cost and volume 3) ZCS tum-on and ZVS tum-off of switches regardless of voltage and load variation 4) ZCS tum-off of diodes leading to negligible voltage surge associated with the diode reverse recovery 5) no additional start-up circuitry required since operating duty cycle range is not limited unlike other current-fed converters with passive clamp 6) significantly reduced current rating of the clamp capacitor, compared to other current-fed converters with active clamp. Experimental results on a 50kHz, 5kW prototype are provided to validate the proposed converter.

simple structure and small switch count, but suffers from excessive power losses dissipated in the RCD snubber and associated with hard switching of main switches. The duty cycle of the three-phase current-fed converter with passive clamp is also limited, leading to necessity of the additional start-up circuit and poor dynamic responses to line and load variations. The three-phase current-fed converter with active clamp has three topologies: push­ pull[5], full-bridge[6] and half-bridge[7-8]. The three­ phase current-fed converter with active clamp is able to achieve ZVS turn on of main switches as well as clamp the voltage surge across the main switch. Also, it does

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