An Online Power-Balancing Strategy for a Parallel Hybrid Electric Vehicle Assisted by an Integrated Starter Generator

Power-flow-control techniques that are capable of handling inefficiencies of both the electric motor/generator (EMG) and the internal combustion engine (ICE) are required to fully explore the fuel-saving potential of fully hybridized parallel hybrid electric vehicles (PHEVs). We propose an online power-flow-control strategy for fully hybridized PHEVs based on the power-balancing strategy (PBS), which controls the ICE within its peak-efficiency region by using the electrical system. We introduce a new PHEV assisted by an integrated starter generator (ISG) or ISG-assisted PHEV, in which the ISG supports the downsized EMG to maintain the electrical system´s efficiency close to its peak efficiency and, therefore, to enhance the fuel-saving capability of the PBS controller. The key contributions of this study are given as follows: 1) identification of the ICE´s peak-efficiency region as a function of the discharging and recharging efficiencies of the electrical system; 2) a new more fuel-efficient HEV architecture; and 3) proper regulation of the state of charge while maintaining infrequent stopping and restarting of the ICE by direct control of the ICE´s energy output. Results show that the PBS controller achieves fuel efficiencies similar to the offline benchmark controller using the equivalent consumption minimization strategy. The PBS controller saves up to 9.3% of fuel on the ISG-assisted PHEV, compared with an equally powered PHEV without the ISG.