Transactions on Industrial Electronics

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  • Topic: Transformer, Quadrature amplitude modulation, Modulation
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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 59, NO. 7, JULY 2012

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Efficiency-Optimized High-Current Dual Active Bridge Converter for Automotive Applications Florian Krismer, Student Member, IEEE, and Johann W. Kolar, Fellow, IEEE Abstract—An efficiency-optimized modulation scheme and design method are developed for an existing hardware prototype of a bidirectional dual active bridge (DAB) dc/dc converter. The DAB being considered is used for an automotive application and is made up of a high-voltage port with port voltage V1 , 240 V ≤ V1 ≤ 450 V, and a low-voltage port with port voltage V2 , 11 V ≤ V2 ≤ 16 V; the rated output power is 2 kW. A much increased converter efficiency is achieved with the methods detailed in this paper: The average efficiency, calculated for different voltages V1 and V2 , different power levels, and both directions of power transfer, rises from 89.6% (conventional phase shift modulation) to 93.5% (proposed modulation scheme). Measured efficiency values, obtained from the DAB hardware prototype, are used to verify the theoretical results. Index Terms—Battery chargers, circuit optimization, dc-dc power conversion, design methodology, digital systems.

Popt,b,min

Popt,a,hi Pmax TS V1 V2 V2,lim vT1 vT2

Minimum power of the high-power mod. scheme for V2 ≥ V2,lim (Popt,b,min > P ,b,max ). Transition power level with D1 = D2 = 0.5 for V2 ≤ V2,lim (Popt,a,hi > Popt,a,min ). Maximum output power of the DAB. Switching period, TS = 1/fS . HV port voltage. LV port voltage. Defines the boundary between different operating modes of the DAB. AC volt. generated by the HV full bridge. AC volt. generated by the LV full bridge. I. I NTRODUCTION

N OMENCLATURE D1 D2 ϕ fS iT1 iT2 IS1,sw,min IS2,sw,opt L n P1 P2 Pout Pout,d P ,a,max P P ,b,max

,V2 lim,max

Popt,a,min

Duty cycle used for the HV full bridge. Duty cycle used for the LV full bridge. Phase angle between vT1 and vT2 . Switching frequency. Transformer current, HV side. Transformer current, LV side. Minimum HV MOSFET current needed to achieve low switching losses, HV side. LV MOSFET current needed to achieve minimum switching losses on the LV side. DAB converter inductance. Transformer turns ratio. HV port power. LV port power. Converter output power. Designated output power (mod. scheme). Maximum power of the modified triangular current mode modulation for V2 ≤ V2,lim . Maximum power of the modified triangular current mode modulation for V2 ≥ V2,lim . Maximum power of the modified triangular current mode modulation at V2 = V2,lim . Minimum power of the high-power mod. scheme for V2 ≤ V2,lim (Popt,a,min > P ,a,max ).

Manuscript received December 20, 2009; revised June 16, 2010 and October 6, 2010; accepted January 24, 2011. Date of publication February 7, 2011; date of current version February 17, 2012. The authors are with the Power Electronic Systems Laboratory, Swiss Federal Institute of Technology (ETH) Zurich, 8092 Zurich, Switzerland (e-mail: krismer@lem.ee.ethz.ch; kolar@lem.ee.ethz.ch). Digital Object Identifier 10.1109/TIE.2011.2112312

ECENT trends in the automotive industry toward electric vehicles, hybrid electric vehicles, and fuel-cell-powered vehicles create the need for highly compact, lightweight, and efficient power converters [1], to exchange electrical power between the various on-board power sources [2]. In order to further push existing limits, a procedure for efficiency-optimized converter design and modulation scheme are presented for a bidirectional automotive dc/dc converter. The dc/dc converter investigated here transfers power between the high-voltage (HV) dc port of a fuel cell stack and the dc port of a low-voltage (LV) battery [3], [4]. The converter specifications are: • HV port: 240 V ≤ V1 ≤ 450 V, nominal voltage: 340 V; • LV port: 11 V ≤ V2 ≤ 16 V, nominal voltage: 12 V. The rated output power of the dc/dc converter considered here is 2 kW within the above specified voltage ranges and bidirectional...
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