Battery Power Management in Heavy-duty HEVs based on the Estimated Critical Surface Charge
MICHIGAN UNIV ANN ARBOR
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Real time battery performance in a Hybrid Electric Vehicle HEV is significantly affected by the battery allowable power limits. This is particularly true in the case of large vehicles, where rates of energy flows through the system reach up to the marginal values during aggressive acceleration or braking. The underlying phenomenon determining the limits is closely connected to the critical surface charge CSC defined by the average positive electrode concentration at the solid particle surface in the cell. This paper characterizes the CSC under high discharging power with respect to the initial battery state of charge SOC, and subsequently utilizes the insight to propose a novel approach to design supervisory control of a series HEV. The new strategy includes a battery power management logic that prevents battery over-charging and overdischarging under aggressive driving conditions. The CSC estimated by the extended Kalman filter EKF is processed with a finite impulse response FIR filter to smooth out short-term fluctuations and highlight longer-term trajectories. Then, the filtered CSC sequence is used to determine the battery allowable power limits in real time and feedbacked to the supervisory controller. The proposed strategy is implemented in the heavy-duty HEV simulation framework and its effectiveness is validated under an aggressive real-world military cycle. Undesirable battery operations and potential possibility of the complete Lithium-ion depletion are prevented, thus improving battery health prospects without any penalty on fuel efficiency.
- Electrochemical Energy Storage