Nonlinear attitude tracking control for four-wheel-leg-vehicle with series active suspension

This study proposes the active disturbance rejection control (ADRC) algorithm to decouple the attitudes of the nonlinear active suspension system of a four-wheel-leg-vehicle (FWLV) system and solve its attitude-tracking problem. Current technologies control the attitude state variables of the vehicle typically at 0° to maintain the car body at a horizontal inclination. However, in complex terrains, the centre of gravity needs to be elevated to improve passability or reduce the centre of gravity to increase driving stability. During steering or braking, the pitch or roll angle of the body needs to be actively changed to improve the gripping force and reduce the possibility of rollover. This study considered the non-linear characteristics of shock absorbers and exploited the advantages of the active disturbance rejection technology, such as high tracking efficiency and small overshoot, to achieve stable tracking. The stability of the tracking attitude angle is analysed within the Lyapunov framework. Simultaneously, a linear suspension attitude-tracking control algorithm is designed as a linear quadratic regulator (LQR) for verifying the tracking control performance of the FWLV. The accuracies of the two algorithms were compared under stationary state, single-side sinusoidal, and random pavement conditions through simulations and vehicular tests. The results indicate that the stability of the attitude-tracking values by ADRC is better than that by the LQR. In addition, comparisons between the simulations and tests illustrated the validity of the active attitude-tracking system.