Drivetrain-Integrated DC-DC Converter for 48 V Network Vehicles
Final Report Abstract
The electric drivetrain is unlikely to push the internal combustion engines out of the market, at least for another few decades. It is predicted that, although close to 90% of passenger vehicles manufactured in 2030 will be electrified, more than 75% of these vehicles will still carry internal combustion engines. About half of the vehicles manufactured in 2030 will be mild hybrids, employing 48 V networks for the electrification of the drivetrain. Along with ignition and traction assistance functions, most power consuming subsystems of the vehicle electronics are migrated to 48 V to achieve higher efficiency levels and lower costs in these mild hybrid vehicles. On the other hand, it is both economically and technically more reasonable to keep the supply voltages of the low-power automotive electronics at 12 V. Therefore, a stand-alone dc-dc converter is employed to supply the 12 V network. In this project, a novel drivetrain with integrated dc-dc converter topology and a control algorithm has been proposed, which enables power transfer between the 48 V and 12 V networks using the starter-generator and its inverter instead of a stand-alone dc-dc converter to save cost, weight and volume. Considering the production volume of mild hybrid drivetrains in the next decade, eliminating this dc-dc converter can have a massive impact on the industry. The drivetrain with integrated dc-dc converter consists of a synchronous machine and a conventional three-phase inverter with an additional half-bridge leg, which controls the zerosequence current across the machine. The zero-sequence current is utilized to transfer power between the 48 V and 12 V networks. This power transfer is independent of the machine speed and torque. Therefore, the integrated dc-dc converter can operate without any degradation on the operation range of the machine. The project demonstrated, that the proposed drivetrain topology is functional and feasible. Experimental results, obtained from prototypes that employ machines with different stator and rotor geometries, show that the efficiency of the drivetrain with integrated dc-dc converter is comparable to a drivetrain with a stand-alone dc-dc converter throughout the whole operating range. Furthermore, contrary to common misconception, the presence of a small amount of zero-sequence current neither saturates the core, nor generates significant losses.
