Optimal Direct Yaw Control for Four Wheel Independent Drive Electric Vehicle

Abstract

This thesis describes the development of a drivetrain control system for Revolve NTNU which competes in the Formula Student series. A yaw rate based Direct Yaw Control(DYC) Torque Vectoring(TV) strategy has been implemented on a 4 Wheel Independent Drive Electric Vehicle (4WID-EV). A Quadratic Program(QP) was formulated to handle the overdetermined problem imposed by four actuators(motors) and two objectives(acceleration and corrective moment). The problem is subject to a set of inequalities imposed by achievable motor torque and estimated friction capacity. A weighted objective function was formulated to explicitly prioritize between stability, traction and response. The quadratic program is solved with an active set based algorithm by iteratively formulating and solving equality constrained problems. The Torque Vectoring control system further features two independent closed loop PID based controllers namely power limiter and traction control. The control system was developed in MathWorks' MATLAB Simulink. Full Vehicle simulations were conducted in IPG CarMaker to validate the control modules. The control system was further deployed on the Engine Controller Unit(ECU) which is an Atsam e70n21 micro controller using MathWorks' Embedded Coder to generate C code to be compiled with the rest of the ECU-project in Atmel Studio. A Hardware In the Loop (HIL) verification test was conducted with a PCIe-CAN interface from PEAK, enabling communication between the vehicle simulation in CarMaker and the Physical ECU through Simulink and MathWorks' Vehicle Network Toolbox. The proposed solution significantly improves both the lateral, longitudinal and dynamical capabilities of the vehicle, compared to a equal torque distribution.