Nonlinear MPC-based slip control for electric vehicles with vehicle safety constraints

Abstract

This paper presents a new slip control system for electric vehicles (EVs) equipped with four in-wheel motors, based on nonlinear model predictive control (nonlinear MPC) scheme. In order to ensure vehicle safety, wheel slip stable zone is considered as time-domain constraints of the nonlinear MPC. Besides, the motor output torque is limited by the motor maximum torque, which varies with motor angular velocity and battery voltage, so the motor maximum output torque limitation is considered as system time-varying constraints. The control objectives include: vehicle safety, good longitudinal acceleration and braking performance, preservation of driver comfort and lower power consumption. This paper utilizes nonlinear MPC to solve this complex optimization control problem subject to the constraints, and the vehicle safety objective is achieved by wheel slip stable zone constraints, the other objectives are realized by adding additional cost functions. In addition, a penalty on the slack variables is also added to ensure that the state constraints (wheel slip) do not cause infeasible problems. The effectiveness of the proposed controller is verified in the off-line co-simulation environment of AMESim and Simulink, and a rapid control prototyping platform based on Field programmable gate array (FPGA) and dSPACE is completed to evaluate the real time functionality and computational performance of the nonlinear MPC controller.