Search Results

The drive to improve and optimize hybrid vehicle performance is increasing with the growth of the market. With this market growth, the automotive industry has recognized a need to train and educate the next generation of engineers in hybrid vehicle design. The University of Waterloo Alternative Fuels Team (UWAFT), as part of the EcoCAR 3 competition, has developed a control strategy for a novel parallel-split hybrid architecture. This architecture features an engine, transmission and two electric motors; one pre-transmission motor and one post-transmission motor. The control strategy operates these powertrain components in a series, parallel, and all electric power flow, switching between these strategies to optimize the energy efficiency of the vehicle. Control strategies for these three power flows are compared through optimization of efficiencies within the powertrain.

Inspection of cell internal resistance (Rint) derived by the hybrid pulse power characterization (HPPC) tests indicates that Rint is a function of relative capacity (state of charge, or SOC), thus some SOC ranges are more efficient than others. Therefore energy losses can be minimized by placing charge sustaining operation in a more efficient SOC range. This creates three operational stages; the initial charge depleting stage to an efficient SOC, a charge sustaining stage until a recharge station is within reach, and a final charge depleting stage until arrival. When coupled with a known drive distance, this three segment Internal Resistance Based (IRB) control strategy increases the extended range electric vehicle (EREV) net battery efficiency from 96.8 to 97.3 % with an associated 14 % decrease in energy losses across the urban domestic drive schedule.