Robust control of farming tractors with dynamic disturbances based on sliding mode observers

This paper considers the problem of farming tractors working in agriculture fields. Agricultural fields are usually uneven and have low friction. Thus tractors undergo more lateral disturbances and slippage than traveling on hardened surfaces. In such scenarios, kinematic models are not adequate to describe the vehicle's motion due to the lateral slip, thus may lead to poor performance. In this paper, a dynamic tractor model is established considering vehicle side slip and lateral force disturbance. A sliding mode observer is proposed to estimate the disturbances and vehicle states which are difficult for direct measurement (especially for the lateral force). In order to attenuate the influence of unknown lateral force disturbance and parameter perturbations, the H
_∞
robust controller based on linear matrix inequality (LMI) approach is designed to reduce the lateral offset of the tractor. Simulation results verified the effectiveness of the proposed method and showed superior performance than LQR controllers.