Hierarchical Control Coordination Strategy of Six Wheeled Independent Drive (6WID) Skid Steering Vehicle

Due to advantages over conventional axle drive systems, AWAID (all wheel independent drive) vehicle are getting popularity in special purpose as well as commercial purpose vehicle. Maneuverability is not only dependent on the steering mechanism but also the steering control. Considering distributed independent drive differential speed steering vehicle, a theoretical hierarchical control allocation problem has been formulated and optimization technique has been employed to solve it and distribute the control to actuators for 6WID (six-wheel independent drive) vehicle. Mathematical technique (quadratic programming) has been applied to solve the optimized control allocation problem. The control strategy can realize the real-time torque distribution, wheel failure and wheel slip limitation. Power distribution strategy in the different mode of vehicle operation is proposed based on the characteristics curves of in-wheel motors in the upper-level layer controller considering corresponding actuator torque output from the lower level controller. The strategy is responsible for executing the same fraction of steering command instructed with or without penalizing the straight driving command. The co-simulation result validates the control strategy in normal working condition and case of handling failure of the wheel.