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

Before the automotive industry completes moving the 14V vehicle loads to the 42V net, HEVs and fuel cell vehicles will likely employ a triple voltage - 14V/42V/High-voltage (200-500V) 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 soft-switching, 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.