Active-Clamp Flyback Converter as Auxiliary Power-Supply of an 800 V Inductive-Charging System for Electric Vehicles

Abstract

Investigation of active-clamped flyback (ACF) dc-dc converter 57 W used as the auxiliary power-supply (APS) of an inductive-charging system (ICS) is presented. The ACF was supplied from variable-dc-link 800 V which was challenge for its design. Anyway, some findings are applicable to any ACF. An overview of ACF control ICs is presented revealing that only two vendors have appropriate devices for ICS. The key-parts' choice and suggestion of new features targeting ACF in this emerging-application are given. Striving for high switching-frequency in ICS is not needed due to large safety-distances of transformer. Measured ''maximum-efficiency vs. magnetizing-inductance'' graph showed that extremes are reached for 400 µH. It was based on four transformers with manually-optimized resonant-tanks. Measurements of ''circulating-power losses vs. input-voltage'' are compared for several transformers. Those losses are in the range of few watts and increase with input-voltage. Measurements of ''bandwidth, phase-margin and gain-margin vs. input-power'', for different input-voltages, are discussed. Those quantities were changeable with load and input-voltage as expected. The short-circuit behavior is analyzed showing that usage of the hybrid-clamp with multi-mode control-ICs is mandatory. Finally, comparison with conventional flyback and quasi-resonant flyback converters showed that both are ≈23 % cheaper, occupy ≈11 % less board-space, and have similar or higher efficiencies. The reason for such efficiency is that ACF circulating-power losses were high as well as dc-voltage-conversion-ratio. Although this is a drawback, for an APS the efficiency is not the key-parameter as long as there are no thermal problems. Moreover, as ACF converter is known for having less EMI-problems that could be the key-advantage for this application. But problem is not-enough electronic components on the market that are suitable for ICS.INDEX TERMS Active-clamped flyback, auxiliary power-supply, control, dc-dc converter, inductive charging-system, quasi-resonant flyback. NOMENCLATURE ACF active-clamped flyback. ACM active-clamping mode. APS auxiliary power-supply. CCM continuous conduction-mode. DCM discontinuous conduction-mode. EMI electro-magnetic interference. EV electric vehicle. FET field-effect transistor.The associate editor coordinating the review of this manuscript and approving it for publication was Alfeu J. Sguarezi Filho .

Active-clamped flyback DC-DC converter in an 800V application: Design notes and control aspects

“…1. The APS connection-point in the ICS An ACF is different from conventional flyback converter in a sense that a bidirectional switch (QH) is introduced instead of the clamping diode in a passive RCD (resistor-capacitor-diode) snubber [4,5]. The QH is actively controlled to increase ACF efficiency by storing energy in the clamping-capacitor C C ) then releasing it to the secondary side [4].…”

“…Its mainstream application nowadays is as power adapter and sometimes with GaN transistors [2,3]. Typically, the ACF is supplied from the rectified single-phase mains [4,5]. Its general analysis, operation, and design are well explained in [6][7][8][9] so readers shall check those references for more information.…”

“…The first reported ACF application in a system with higher-DC-input-voltage (HDCIV) of 800 V was [4] followed by [5]. In those papers the 57 W ACF was used as an auxiliary power-supply (APS) of primary (ie ground) side of an inductive-charging system (ICS) for wirelesscharging of battery electric-vehicles (BEV).…”

“…Motivation to writing this paper was to present missing theoretical considerations, simulation, and experimental results for the ACF that were not covered in [4] and [5]. Focus here is on transformer measurements, cross-regulation and control aspects with comparison to conventional flyback DC-DC converter.…”

“…Focus here is on transformer measurements, cross-regulation and control aspects with comparison to conventional flyback DC-DC converter. This article is a companion to [4] and [5]. Note that this article does not introduce a new topology or a control method but evaluates usage of the known topology (ACF) in an emerging application (ICS).…”