Finite Control-Set Model Predictive Torque Control of Nonsinusoidal PMSM: a Generalized Approach for Torque Ripple Mitigation and MTPA Operation

Permanent Magnet Synchronous Motors (PMSMs) may present spatial harmonics depending on the design guidelines or imprecisions on the manufacturing process. The interaction of conventional sinusoidal current feeding strategies with these spatial harmonics can produce a considerable torque ripple. This paper deals with a modified Finite Control-Set Model Predictive Torque Control (FCS-MPTC) loop as an active torque ripple minimization solution for PMSMs with spatial harmonics. The proposed approach designs a novel cost function, based on the cross product reactive instantaneous power theory. The benefits of the proposed generalized approach include providing smooth torque production and the Maximum Torque per Ampère (MTPA) operation on PMSMs with a number of spatial harmonic sources, including those on zero-sequence. The effectiveness of the presented control strategy is demonstrated comparatively to conventional sinusoidal current feeding strategy on a PMSM drive employing a three-phase four-leg two level voltage source inverter under both steady and transient state.

Reducing Rotor Temperature Rise in Concentrated Winding Motor by Using Magnetic Powder Mixed Resin Ring

The demand for high-speed servomotors is increasing, and minimal losses in both high-speed and high-torque regions are required. Copper loss reduction in permanent magnet motors can be achieved by configuring concentrated winding, but there are more spatial harmonics compared with distributed winding. At high-speed rotation, the eddy current loss of the rotor increases, and efficiency tends to decrease. Therefore, we propose a motor in which a composite ring made from resin material mixed with magnetic powder is mounted on the stator to suppress spatial harmonics. This paper describes three characteristic motor types, namely, open-slot motors, composite-ring motors, and closed-slot motors. Spatial harmonics are reduced significantly in composite-ring motors, and rotor eddy current loss is reduced by more than 50% compared with open-slot motors. Thermal analysis suggests that the saturation temperature rise value is reduced by more than 30 K. The use of a composite ring is effective in reducing magnet eddy current loss during high-speed rotation. Conversely, the torque characteristics in the closed-slot motor are greatly reduced as well as the efficiency. Magnetic circuits and simulations show that on electrical steel sheets with high relative permeability, the ring significantly reduces the torque flux passing through the stator, thus reducing the torque constant. To achieve reduced eddy current loss during high-speed rotation while ensuring torque characteristics with the composite ring, it is necessary to set the relative permeability and thickness of the composite ring according to motor specifications.

Torque Ripple Reduction of DTC Based on an Analytical Model of PMSM

Aiming at the torque ripple problem of direct torque control that is based on space vector pulse width modulation (SVPWM-DTC) caused by the spatial harmonics and magnetic saturation characteristics of permanent magnet synchronous motor (PMSM), a feedforward controller based on an analytical model of PMSM was designed. An analytical motor model taking the spatial harmonics and magnetic saturation characteristics of PMSM into account by reconstructing the numerical solution of magnetic co-energy (MCE) from finite element analysis (FEA) was proposed. Based on that, the optimal stator flux linkage that minimizes the torque ripple is calculated and then a feedforward controller is designed and added to the SVPWM-DTC framework. Simulations and experiments are carried out and the results show that the proposed feedforward controller can effectively reduce the torque ripple of SVPWM-DTC.