Flatness-Based Torque Control of Saturated Surface-Mounted Permanent Magnet Synchronous Machines

Modern permanent magnet synchronous machines (PMSMs) may also be operated in regimes where significant magnetic saturation occurs. Classical fundamental wave models do not incorporate magnetic saturation in a systematic way. Mostly, only heuristic extensions can be found in the literature. Control schemes based on such dq0-models are thus often unable to achieve the given control demands. This paper proposes a flatness-based torque control strategy for a saturated surface-mounted PMSM. Different to existing works, magnetic saturation is considered in a thorough and physically consistent way. Based on a calibrated magnetic equivalent circuit model of the PMSM, a simplified model suitable for the flatness-based controller design is derived. The proposed 2-DOF control scheme inherently accounts for the mutual coupling of the phase windings. Furthermore, the time-varying controller gains are obtained by pole placement technique. In contrast to the majority of controllers used for PMSM control, the proposed control scheme is formulated in the stator-fixed reference frame, and hence, no coordinate transformation is necessary. The flatness-based torque controller is implemented on an experimental test bench. An accelerated run-up of the PMSM with about four times the rated torque is performed to highlight the feasibility of the proposed approach. Finally, the flatness-based torque controller is compared with a common vector control implementation based on a dq0-model of the motor.