INTRODUCTION Increasing global environmental concern requires that automobiles be cleaner and more fuel-efficient. In this context, vehicle electrification is quite promising because of the high-efficiency of powertrain systems and reduced, or zero, emissions [ 1,2]. Because of the actuation flexibility of their systems, over-actuated electric vehicles with individual driving systems, including in-wheel and on-board motors, are a very popular research topic amongst various types of electrified powertrain architectures [ 3, 4, 5]. The introduction of the individual electric powertrain provides great capacity for improvement of the vehicle’s energy efficiency and control performance. However, it also poses tremendous challenges concerning vehicle safety, since the system dynamics of the electric powertrain are very different from those of conventional vehicles. Furthermore, cooperation mechanisms between multi-actuators, including motors, brakes, and steering, are quite complex. Therefore, the safety factor for various types of driving conditions is of great significance in the design and control of over-actuated electric vehicles.Robust Control of Regenerative and Hydraulic Brakes for Enhancing Directional Stability of an Electric Vehicle During Straight-Line Braking Chen Lv, Junzhi Zhang, and Yutong Li State Key Lab of ASE, Tsinghua Univ. Bolin Zhao Technische Universiteit Eindhoven Ye Yuan State Key Lab of ASE, Tsinghua Univ. ABSTRACT Thanks to the actuation flexibility of their systems, electric vehicles with individual powertrains, including in-wheel and on-board motors, are a very popular research topic amongst various types of electrified powertrain architectures. The introduction of the individual electric powertrain provides great capacity for improvement of the vehicle’ s ener gy efficiency and control performance. However, it also poses tremendous challenges concerning vehicle safety, due to the complex system dynamics and cooperation mechanisms between multiactuators. For an electric vehicle with independently controlled motors, because of design and manufacturing factors, the steady-state error of each motor output torque, and the flexibilities and nonlinear backlash of left and right drivetrains, can be dif ferent. This results in asymmetrical output characteristics of electric powertrain systems on the same axle. Therefore, during a normal straight-line deceleration, an unexpected yaw moment would be generated, affecting vehicle’s directional stability. In this study, a novel method of directional stability enhancement through robust control of blended braking of an electric vehicle equipped with four individual on-board motors during normal straight-line deceleration are studied. System models, including the vehicle dynamics, tire, electric powertrain, and hydraulic brake models, are developed. Mechanisms of directional instability of the electric vehicle during straight-line braking are analyzed. To further improve the electric vehicle’s safety and performance, robust control algorithm of blended braking is developed using nonlinear sliding mode approach. Simulations of the proposed control strategy is carried out under straight-line braking. The results demonstrate that the developed approach is advantageous over the baseline, with respect to both the directional stability and regeneration efficiency , thus validating the feasibility and ef fectiveness of the controller synthesis. CITATION: Lv, C., Zhang, J., Li, Y ., Zhao, B. et al., "Robust Control of Regenerative and Hydraulic Brakes for Enhancing Directional Stability of an Electric Vehicle During Straight-Line Braking," SAE Int. J. Alt. Power. 5(2):2016, doi:10.4271/2016-01-1669.2016-01-1669 Published 04/05/2016 Copyright © 2016 SAE International doi:10.4271/2016-01-1669 saealtpow.saejournals.org 328Downloaded from SAE International by University of Liverpool, Saturday, September 08, 2018Existing studies of over-actuated electrified vehicles wi