Energy-oriented speed profile optimization for electric vehicles considering road horizontal curvature

Improving the energy efficiency of electric vehicles (EVs) to extend their driving ranges is an active area of research in both the academia and industry. Speed profile optimization has drawn a lot of attention due to its effectiveness in energy conservation, particularly in straight line driving scenarios. However, a lack of work has been reported in understanding eco-driving under cornering conditions. To this end, this paper proposes an energy-optimal speed profile optimization approach for EVs when negotiating curve roads. Firstly, an adapted step size Newton Iteration algorithm is proposed to calculate the cornering resistance based on a nonlinear 7 degree-of-freedom (7-DOF) vehicle model. Secondly, an exhaustive search method is presented to investigate the effect of curve radius on the optimal steady-state cornering speed. Thirdly, in order to calculate the optimal speed profile for the curves with varying curvature, a dimensionality-reduction nonlinear optimization problem is established, with air drag, cornering resistance, motor torque limitation and speed limit in presence. Finally, a dynamic programming (DP)-based algorithm is devised to calculate the global optimal speed profile along the entire curve which contains tangents and core curve. Simulation experiments show that the proposed method can reduce energy consumption by up to 12.84% and 6.29% when driving on a route with single curve and a real-world urban route, compared to the driving patterns with typical driver model (TDM), respectively. The method presented in this work can be employed to speed advisory systems to save energy and extend the driving range of EVs.