Optimal Energy Management for a Hybrid Electric Vehicle with a Power Split Supercharger

This work investigates the utilization of a micro-hybrid mechanism on fuel economy improvement of a vehicle with a downsized engine. The micro-hybrid system, configured with a motor, a planetary gear set and a supercharger, permits switching between parallel hybrid operation and boosting but not both. This constrained flexibility offers additional degrees of freedom, yet it requires a highly optimized decision of which functionality, torque assist or boost assist, in addition to how much energy to be used by each functionality. This unique power split supercharger (PSS) enables the use of a downsized engine as a competitive counterpart to widely used turbochargers and further implements micro-hybrid functionalities such as start-stop, regenerative braking and limited torque assist. The optimal control problem for energy management of a vehicle with an automatic transmission is formulated and solved using dynamic programming (DP) over standard drive cycles. The results indicate 25.2% fuel consumption reduction compared to a baseline turbocharged engine over the FTP75 drive cycle. It is also shown that for the range of operating points that can be realized with both torque assist and boosting, torque assist is often the optimal operating mode and boosting is mostly used when the required torque exceeds the torque of the naturally aspirated engine plus the motor, hence points to a simple strategy that can be near optimal.