A low cost, triple-voltage bus DC-DC converter for automotive applications

Before the automotive industry completes moving the 14 V vehicle loads to the 42 V net, HEVs and fuel cell vehicles will likely employ a triple voltage-14 V/42 V/high-voltage (200~500 V) bus system. This paper presents a low-cost, soft-switched, bidirectional DC/DC converter for connecting the three voltage nets. The converter consists of two half-brides and a high-frequency transformer, which provides voltage level matching and galvanic isolation between the two half-bridges for safety requirements. The use of dual half-bridges minimizes the number of switching devices and their associated gate drive components. Moreover, snubber capacitors and the transformer leakage inductance are utilized to achieve soft-switching. Therefore, no extra active switches or passive resonant components are required for softswitching, further reducing component count. Control of power flow among the three voltage buses is achieved by adjusting the duty ratio and phase angle between the half-bridge output voltages. Simulation and experimental data on a 2 kW lab unit are included to verify the power flow control scheme