Analysis of downshift’s improvement to energy efficiency of an electric vehicle during regenerative braking

Liang Li, Xujian Li, Xiangyu Wang, Jian Song, Kai He and Chenfeng Li

Applied Energy, 2016, vol. 176, issue C, 125-137

Abstract: Downshift during regenerative braking helps to improve the energy efficiency of electric vehicles. Two main problems are involved in the downshift process. One is the determination of optimal downshift point, and the other is the cooperative control of regenerative braking and hydraulic braking. In order to achieve a systemic solution to these problems, a hierarchical control strategy is brought forward for an electric vehicle with a two-speed automated mechanical transmission. For the upper controller, an off-line calculation and on-line look-up table method is adopted to obtain the optimal downshift point, and a series regenerative braking distribution strategy is designed. For the medium controller, a nonlinear sliding mode observer is designed to obtain the actual hydraulic brake torque. For the lower controller, cooperative control of regenerative braking and hydraulic braking is given to ensure brake safety during downshift process, and a resembling pulse width modulation method is proposed to regulated the hydraulic brake torque. Simulation results and hardware-in-loop test show that the proposed algorithm is effective in improving the energy efficiency of electric vehicles.

Keywords: Electric vehicle; Regenerative braking; Energy efficiency; Optimal downshift point; Hierarchical control; Sliding mode observer (search for similar items in EconPapers)
Date: 2016
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (29)

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DOI: 10.1016/j.apenergy.2016.05.042

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