Novel Concepts for Integrating the Electric Drive and Auxiliary DC-DC Converter for Hybrid Vehicles

Cost, volume, and weight are three major driving forces in the automotive area. This is also true for hybrid electric vehicles, which are attracting more and more attention due to increasing fuel costs and air pollution. In hybrid vehicles, the energy distribution system causes a significant share of the volume and the costs. One part of this system is the dc-dc converter that transfers power between the low- and high-voltage buses. In order to reduce the costs and the volume of this converter, this paper presents a new concept for integrating the dc-dc converter functionality into the traction drive system. By using the inverter and the machine to implement a primary bridge leg of an isolated full-bridge dc-dc converter, the total system costs and weight can he reduced. This concept is verified by simulations and experimental results for a scaled prototype. An analytical model of the system has been developed and agrees very well with the measurements. By scaling this model to the power levels typical for hybrid vehicles, it is expected that the efficiency for the dc-dc converter will be greater than 85% for a conventional modulation scheme and above 91% for an optimized switching scheme.