Observer-Based Traction-Force Control with Slip-Constrained Electric Wheel-Drive Actuation for an Agricultural Tractor

Electric wheel-drive actuators offer rapid and precise torque regulation, yet translating motor torque into commanded ground traction force remains challenging under deformable terrain interactions and wheel-slip constraints. This study proposes an observer-based traction-force control architecture for an electric agricultural tractor, formulating traction tracking as a constrained actuator-control problem. To avoid fragile and expensive wheel-force transducers, a causal physics-informed ridge observer estimates dynamic longitudinal wheel–soil interaction forces online using standard onboard kinematic and actuator signals. The observed force is then integrated into a feedback PI regulator coupled with a dynamic anti-windup slip limiter to prevent excessive soil shear failure. Evaluated on a high-fidelity single-wheel testbed in the Genesis physics engine across contrasting tilled and compacted soils, the causal observer achieves accurate dynamic force estimation with normalized RMSE below 0.15%. Under nominal tillage operations across 1.0 and 2.0 m/s forward speeds, the closed-loop controller achieves sub-1.5% steady-state force tracking. Under excessive traction demands near the terrain adhesion limit, the dynamic slip limiter actively intervenes to prevent runaway wheel spin-out, strictly bounding peak slip below 18.2% and sustaining stable traction at the physical boundary. This framework provides a sensor-efficient and robust solution for precise traction regulation in electric off-road vehicles.