DC/DC converter for HEVs and resonant active clamping technique

Alternative powertrains such as hybrid electric vehicles (HEV) and full electric vehicles (EV) is rapidly advancing fueled by the rising cost of crude oil and the global need of environmentally friendly transportation. The vehicles electrification is not only involving the traction parts, but it is generating new applications for the electric power conversion. One of the new blocks inside the hybrid electric vehicles is a bidirectional DC-DC converter for auxiliary power supply of electric loads. Compared to traditional DC-DC converters for similar applications, the proposed topology has the advantages of a simple circuit capable of bi-directional energy transfer from the 12V DC bus and the high voltage DC bus used for traction. Active clamping implementation in the boost mode and soft-switching operation due to phase shift modulation in the buck mode, without additional devices, high efficiency and simple control are key features. The control algorithm is implemented on 32-bit microcontroller, giving high advantages in terms of cost, flexibility and also efficiency increase due to the possibility of easy synchronous rectification implementation. These advantages make the proposed converter promising for medium and high power applications especially for auxiliary power supply in HEVs where the high power density, low cost, lightweight and high reliability are main concerns. The operating principle and theoretical analysis are provided in this paper. The experimental verifications are also presented by means of a 1.5kW lab prototype.