A Novel Control Method for Unmanned Agricultural Tractors: Composite Back-stepping Sliding Mode Path Tracking

A composite back-stepping sliding mode controller is explored in the paper to address the under-actuated, input saturated, and time-varying disturbances, as well as model-dependent issues that bother the path tracking control of unmanned agricultural tractors. Specifically, the path tracking error model is introduced. The extended state observers (ESO) with time-varying parameters are employed to handle the lump disturbances resulting from the external disturbances and model nonlinearity. A novel composite path tracking controller is proposed based on back-stepping and active disturbance rejection control and sliding mode control, whose effectiveness is elaborated by simulations and experiments. According to the results, the proposed controller, whose stability is elucidated in the appendix, outperforms the fuzzy pure pursuit control in reducing the lateral offset.