A disturbance observer-based current-constrained controller for speed regulation of PMSM systems subject to unmatched disturbances

The speed regulation problem of permanent magnet synchronous motor system is investigated under a noncascade structure. Despite its superiority in straightforward control design, simple parameter adjustment, and satisfying system dynamic performance, the structure brings two problems: the overcurrent protection and unmatched disturbance rejection. Under this structure, the current cannot any more be restricted by a reference value, and ought to be constrained within a certain range to ensure the circuit safety. Besides, unmatched disturbances, mainly caused by external load torques, may result in undesired interference and violate the constraint requirement, since they affect the current directly via the same channel. Toward that end, a novel current-constrained control algorithm is designed to tackle the current constraint and unmatched disturbances simultaneously. A disturbance observer (DOB) is utilized for unmatched disturbance estimation. A constraint coping mechanism is constructed to restrict the current. Then, a key nonlinear item is proposed by augmenting the disturbance estimation and the constrained current. Finally, a composite controller is proposed with concise structure and rigorous closed-loop stability analysis. Numerical and experimental tests further validate that the proposed control approach achieves promising speed tracking performance and guarantees the current constraint in the presence of unmatched disturbances