Novel Active Safety Methods For Electric Vehicles With In-wheel Motors Based On Accurate Motor Torque Calculation

Torque is one of the most important control factors for a vehicle's motion.Compared with internal combustion engines,electric motors can have a more accurate torque feedback.In electric vehicles,direct torque control of the permanent magnet synchronous motor has been well studied.However,because of the non-ideal back EMF phenomenon,direct torque control of brushless DC motors has not been widely studied.In this paper,a new method using Kriging to calculate the back EMF in an on-line fashion is presented.Kriging prediction is used to approximate the back EMF of the motor based on information from sampled points.With motor speed and rotor position as inputs,Kriging predicts back EMF as the output that is used to calculate the motor torque with three phase currents.Using this novel method,motor torque can be accurately calculated and implement in micro control units of vehicles,even when facing extremely high/low temperature and aging conditions,which is a crucial problem for motors used in electric vehicles.Experimental tests under the high temperature have been conducted to demonstrate the applicability of the proposed method.Driving electric vehicles by electric motors can bring lots of unique advantages for dynamic traction control of vehicles.With the superior fast and accurate torque control performance of electric motors,electric vehicles can especially achieve higher levels of safety and handling.A simple,effective,and efficient anti-skid control method specified for electric vehicles is proposed in this paper with the consideration of real-world resistance factors.This method is developed based on sensing and regulating a newly defined parameter,TA,the ratio of drive motor torque to wheel angular acceleration,both of which can be easily obtained for electric motors.The monotonic relationship between the slip ratio and TA is proved under both acceleration and deceleration conditions,considering real-world resistance factors.The simulation and experimental results show that TA can be efficiently used,instead of the slip ratio,in anti-skid control.The results indict that electric vehicles can achieve high-performance vehicle motion control with more flexible and simplified configurations by using the existing electric motors not only as drivers but also as actuators and sensors at the same time.With the superior fast and accurate control characteristic of electric motors,electric vehicles can inherently have better performance in the field of active safety and dynamic stability control.With the novel wheel status parameter TA for electric vehicles proposed by the authors in earlier publication,the new TA index(TAI)based rollover detection method is presented in this paper.The three-level electric vehicle control structure is used to analyze the effective control steps for rollover prevention with the newly proposed TAI method.The simulation is conducted using the in-house electric vehicle dynamic model developed by the authors' research group.The simulation results prove the feasibility of using TAI to detect rollover.The experiment uses the electric vehicle equipped with four in-wheel motors in the authors' research lab.The vehicle parameter and performance data are imported to CarSim,which is an industrial standard vehicle dynamic analysis software to run the rollover test.The experimental results also demonstrate that TAI is an effective method in the rollover detection.