Soft-transition automotive inverters with integrated battery charging function

A reduction of the charging time of traction batteries in electric vehicles is a decisive factor for a widespread adoption of this technology. Being constrained by the volume of on-board battery chargers, a direct increase of the charging power would not be a satisfactory option. Thus, innovative solutions have to be sought to break through this limitation. One such solution consists on making use of components present in the powertrain to implement the battery charging function. In this manner, a straightforward approach would be to operate the propulsion drive inverter as a three-phase rectifier. In this case, however, the power density of the system would be restricted by the volume of the input filter inductors. In this publication, a different approach is examined that promises a further increase in power density as well as an improvement of the efficiency of the powertrain. The concept is based on the idea of integrating the battery charger into the resonant auxiliary circuits of a soft switching inverter. Consequently, a reduction in space requirements for the battery charger can be coupled with an improvement in efficiency of the propulsion inverter that ultimately can lead to an enhacement of the overall power density of the system. By means of a practical case study, design aspects of the proposed concept are discussed and its characteristics are investigated.