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

An auxiliary power module in electric vehicles is a dc/dc converter bridging the high-voltage propulsion battery with a low-voltage auxiliary system. In the coming era of connected and autonomous vehicles, the power rating of such dc/dc converters is expected to surge from 2.5 to 6 kW. In addition, there is the challenge of a wide operating voltage range, e.g., 250-450 V required by the high-voltage propulsion battery and 10-16 V at the low-voltage auxiliary battery. To meet these voltage and power challenges, this article proposes a two-stage bidirectional design, i.e., interleaved buck + dc transformer (DCX) that offers full voltage range coverage, 3.5 kW rated power, and peak power of >6 kW. Experimental results indicated >96% efficiency, owing to the zero-switching loss of DCX. Furthermore, the precharge mode that charges the input dc-bus capacitor with the low-voltage battery is accomplished using the inner phase shift control of the DCX stage. DC-bias blocking capacitors on the low-voltage side are replaced with a simple, unique dc-bias detection circuit that samples and eliminates the dc-current offset of the transformer. Simulation and test results confirm that the proposed method effectively detects and eliminates the dc-bias current.