Slip control model for an electric tractor with four-wheel independent driving E-axle systems

Most electric agricultural machinery employs motor-based speed control to achieve target velocities. However, increasing torque to maintain speed can cause excessive wheel slip owing to soil sinkage, leading to inefficient energy use. Real-time measurement of motor rotational speed enables accurate slip estimation and facilitates more effective traction control. This study developed and evaluated a slip control model to reduce wheel slip and improve the tractive efficiency of an electric tractor equipped with four-wheel independent driving electric axle (E-axle) systems. The slip was calculated using travel speed and motor rotational speed, and the slip conditions were classified into three types. Based on the type of slip detected, the control model selected either a torque allocator (TA) or crawl mode. The control model was implemented in MATLAB/Simulink and evaluated through co-simulation with a multibody dynamics (MBD) model developed in RecurDyn. The MBD model was validated through weight measurements and experimental traction force tests. Simulation results indicated that the proposed slip control model reduced the slip by 6%–20% in TA mode and 1%–15% in crawl mode, while increasing tractive efficiency by 0.9%–3.8%. The results highlight the practicality of speed-based slip control for electric agricultural machinery and support the design of more efficient traction management strategies.