Fault-tolerant tracking control method for four-wheel distributed electric drive autonomous vehicle

A fault-tolerant tracking control method of a four-wheel distributed electric drive autonomous vehicle, comprising the steps of:

• S0:
• setting initial conditions;
• wherein a four-wheel distributed electric drive autonomous vehicle is equipped with hub motors in four wheels to provide power;
• the actual output torque of each hub motor during normal driving is Ti, i=1, 2, 3, 4, which corresponds to a left front wheel, a right front wheel, a left rear wheel and a right rear wheel, its value is equal to the output torque Tri required for vehicle tracking, i=1, 2, 3, 4, and the output torque of each hub motor is separately and independently controlled by the corresponding motor controller;
• the fault coefficient of each hub motor is set as ξi, i=1, 2, 3, 4, its value is the ratio of the actual output torque Ti of the hub motor to the required output torque Tri, the value range is [0, 1];
• when the fault coefficient of each hub motor of the vehicle is 1, it is in the ideal working state;
• when the fault coefficient of a hub motor is 0, it means that the wheel has completely lost the driving force of the motor;
• when the fault coefficient of a hub motor is between 0 and 1, it means that the wheel motor can still provide some required driving torque;
• the fault identification of the hub motor is set as Si, i=1, 2, 3, 4, when a hub motor works normally, Si is 0, if it is in the fault state, Si is set to 1;
• and
• the power system fault cannot be recovered in a short time by restarting the motor or the vehicle is in a state that does not have the conditions for immediate repair;
• S1:
• obtaining the output torque and the fault coefficient of a hub motor;
• S2:
• fault diagnosis and fault-tolerant tracking, wherein the flow is as follows:
• first, it is judged whether the vehicle power system enters a fault state;
• if the fault coefficient of a certain hub motor is kept below 0.8 for more than 10 s or below 0.2 for more than 2 s, it is considered that the hub motor is in the fault state, Si is set to 1, entering the fault-tolerant tracking link;
• in the fault-tolerant tracking link, first, it is necessary to judge the fault modes of the current vehicle to determine whether the vehicle is in a controllable state at present:
• according to the number and position of the faulty hub motors, the vehicle fault modes are classified into six types, including:
• {circle around (1)} fault of a single motor at any position;
• {circle around (2)} fault of two motors on the same side;
• {circle around (3)} fault of two motors on different sides and same axes;
• {circle around (4)} fault of two motors on different sides and different axes;
• {circle around (5)} fault of three motors at any position;
• {circle around (6)} fault of all four motors;
• according to engineering experience, the vehicle is still in controllable state in {circle around (1)} to {circle around (5)} fault modes, and the vehicle is in completely uncontrollable state in {circle around (6)} fault mode;
• and
• S3:
• using different control logics for different fault modes:
• (1) when the vehicle is in any one of {circle around (1)} {circle around (2)} {circle around (3)} {circle around (4)} fault modes, the vehicle is in a controllable state, the compensation of the transverse and longitudinal driving force of the vehicle is realized through other hub motors and active steering systems working normally, and the vehicle realizes fault-tolerant tracking in {circle around (1)} {circle around (2)} {circle around (3)} {circle around (4)} fault modes through compensation;
• (2) when the vehicle is in {circle around (5)} fault mode, although the vehicle is in a controllable state, the vehicle is capable of only driving at a very low speed and uncapable of tracking effectively in the face of complex paths;
• at this time, the vehicle VCU reports the fault to the path planning layer through the CAN bus;
• after receiving the fault report from the CAN bus, the path planning layer abandons the original planned path and re-plans the path according to the current vehicle driving environment with a safe parking spot as the target;
• the vehicle VCU tracks the re-planned path, drives at a low speed and stops at a safe parking spot at last;
• and
• (3) when the vehicle is in {circle around (6)} fault mode, the vehicle is in an uncontrollable state;
• at this time, the vehicle is uncapable of avoiding danger in an emergency;
• no matter whether the driving environment where the vehicle is located at present is capable of guaranteeing the safety of the vehicle during emergency braking, braking measures should be taken, that is, the vehicle actively cuts off the energy supply of the hub motor, and the brake-by-wire system adopts emergency braking or controlled deceleration braking scheme according to the driving speed of the vehicle at this time.