Compound disturbance suppression strategy for steer-by-wire system with permanent magnet synchronous motor

Compound disturbances in steer-by-wire (SbW) include non-periodic disturbances in the mechanical system and periodic torque ripple in the permanent magnet synchronous motor (PMSM). Compound disturbances lead to degradation of control accuracy and robustness, with repeated deviations in tracking accuracy. Moreover, according to the time-varying conditions of SbW, the frequency of periodic disturbances varies over time. To this end, this paper proposes a compound disturbances suppression strategy that combines spatial domain iterative learning with forgetting factor (SILCFF) and extended state observer (ESO). ESO compensates the non-periodic disturbances to the non-singular fast terminal sliding mode controller (NFTSMC) to track the steering angle and reduce the unknown disturbance boundaries. After disturbance compensation, the system is approximately linearized, making it more suitable for SILCFF designs. SILCFF solves the problem of time-varying iteration cycles caused by the variable speed conditions of SbW, which is difficult to handle by conventional time-domain iterative learning, and compensates for periodic torque ripple. The results indicate that SILCFF can effectively compensate for periodic torque ripple at time-varying frequencies. This strategy can ensure the SbW system has good dynamic steering angle tracking performance and robustness.