Design a 400 V–12 V 6 kW Bidirectional Auxiliary Power Module for Electric or Autonomous Vehicles With Fast Precharge Dynamics and Zero DC-Bias Current

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Abstract
An auxiliary power module (APM) in electric vehicles is a DC/DC converter bridging the high voltage propulsion battery with a low voltage auxiliary system. With the era of connected and autonomous vehicles coming, the power rating of such DC/DC is expected to surge, say from 2.5kW to 6kW. No mention its challenge of wide operating voltage range, e.g., 250~450V input provided by the high voltage propulsion battery and 10~16V at the low voltage auxiliary battery. To meet such voltage and power challenges, this paper proposed a two-stage bidirectional design, i.e., interleaved buck + DC transformer (DCX) offering full voltage range coverage, 3.5kW rated power and peak power of >6kW. Experimental results indicated >96% efficiency, thanks to the zero-switching loss of DCX. In addition, the pre-charge mode to charge the input DC bus capacitor with the low-voltage battery is also achieved using the inner phase shift control at the DCX stage. To save DC-bias blocking capacitors at the low-voltage side, a novel and simple DC bias detection circuit is proposed to sample the DC-current offset of the transformer. Both simulation and test results verified that the proposed method can effectively detect and eliminate the DC bias current.

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