Extended-State-Observer-Based Nonlinear Control for PMSM Servo Systems With Current Constraints and Voltage Saturations

This article focuses on the tracking controller design for permanent magnet synchronous motor (PMSM) servo systems subject to both current constraints and voltage saturations. Toward this end, a novel system transformation technique is first proposed to transform the current-constrained PMSM servo system into an equivalent “unconstrained” one. In particular, to reduce the effects of the current over-constraint (i.e., the excessive constraint on the motor current) on the control performance, a safe boundary is introduced in the proposed system transformation scheme. In this way, the current constraint mechanisms are activated if and only if the current is close to its constraint boundaries. Then, by virtue of the transformed model and the backstepping design procedure, an extended state observer (ESO)-based nonlinear control strategy is developed, where two ESOs are employed to compensate for system disturbances. In addition, an auxiliary system with saturation error serving as the input is established to address the effects of voltage saturation. The theoretical analysis demonstrates that the proposed control strategy guarantees the desired performances under both the current constraint and voltage saturation. Finally, the hardware experiments are performed on a 5.5-kW PMSM to validate the effectiveness of the proposed method.