The predictive current control (PCC) method is based on nominal parameters to predict and control currents of permanent magnet synchronous motors (PMSM). However, there may be mismatches between actual parameters and their nominal values due to material aging, temperature rise, or magnetic saturation. In this paper, the effects of parameter mismatches on system stability and current tracking errors are analyzed theoretically and verified. Furthermore, based on current errors, a robust PCC scheme with parallel compensation terms onto the conventional deadbeat predictive current controller is proposed. Since there is no change introduced into the original controller, the proposed robust PCC method can be easily implemented. Finally, feasibility and validity of the proposed robust PCC scheme against multi-parameter mismatches are confirmed by experiments, in addition, the experimental results show that system steady-state robustness is improved with no cost to transient performance.

Mounted with helical magnets, the magnetic lead screw (MLS) could realize contactless conversion between rotation and linear motion. Since the magnetic field in the MLS is essentially 3-D, previous 2-D analytical magnetic field calculation methods, fail to behave well in the accuracy, while 3-D numerical methods suffer from poorer efficiency in computation time. In this paper, an analytical model is developed to predict the 3-D magnetic field distribution and the electromagnetic performance of the MLS. Both radial and parallel magnetizations of the helical magnets are considered. It is shown that the air-gap magnetic field distribution is closely dependent on the magnetization pattern of helical magnets. Both 3-D finite element (FE) simulation and prototype experiment are performed to validate the accuracy of the proposed analytical model. The analytical results are in good agreement with those by FE analysis and experiment, respectively. And it is highlighted that the magnets magnetized in parallel result in the deformation of thrust force and torque characteristics. Finally, the impact of the number of parallel magnetized magnets on the distortion of MLS performance is discussed. The work can be served as a valuable tool for precise and fast optimization design of the MLS.

This paper presents the theoretical analysis and numerical modeling of various cogging torque suppression methods of the slotted limited angle torque motor(LATM). The relationship between the cogging torque, the output characteristics and the structure parameters of new methods is revealed by derived equations and finite element analysis(FEA), which provides a theoretical basis for the optimization of the slotted LATM. The effectiveness of the best suppression method is verified by the prototype experiment. In addition, a method to predict torque distortion caused by armature reaction is proposed, and it is verified by finite element simulation and prototype experiment.

This paper investigates the performance of a magnetic lead screw (MLS) equipped with skewed arc magnets. Skewed arc magnets are adopted to approximate the helical ones, because the latter is hard to realize. Although similar method had been proposed in the previous literature, discussion about the parameters of the skewed arc magnets was insufficient and little attention was paid to the gear ratio of the resultant MLS. In this paper, the principle of approximation by skewed arc magnets is proposed and discussed, and the performance of the MLS with skewed arc magnets is evaluated and compared with the ideal MLS in terms of thrust force, torque, and gear ratio. It is highlighted that the gear ratio is the fundamental indicator of the MLS's performance, besides the thrust force and torque. It is shown that the gear ratio of MLS is mainly affected by the reference angle and the arc angle of skewed arc magnets, and optimal values for the two angles are obtained. In addition, the effects of the magnet magnetization on thrust force and torque are analyzed. Finally, dovetail budge and groove are introduced between the adjacent magnet segments for simpler fabrication.

Linear permanent magnet (PM) motors have increasingly been used in high performance applications where high accuracy and fast dynamic response are required. However, the presence of cogging force in linear motors compromises position and speed control accuracy, which can be particularly troublesome at low speeds. This study analyses the cogging force characteristics associated with linear PM motors having either single‐layer or double‐layer non‐overlapping windings. It is shown that the effectiveness of cogging force reduction techniques reported in literature is dependent on winding configurations. Linear PM motors with single‐layer windings generally have better potential for cogging force reduction by employing these techniques. In contrast, linear motors with double‐layer windings exhibit considerably higher tooth‐ripple cogging forces even when fractional‐slot per‐pole design is adopted. This, in turn, poses more difficulties in reducing their cogging force.

Low force ripples from permanent magnet linear motors (PMLMs) are typically essential requirements in a wide range of demanding control applications with high motion quality. Apart from the sources present in rotary PM machines, phase unbalance due to the end effect is another major contributor of the thrust force ripples in the PMLMs. In this paper, the phase unbalance and induced force ripples are investigated in the case of a planar PMLM typically equipped with single-layer concentrated windings and quasi-Halbach magnets. It demonstrates that although the PMLM is quite carefully deigned to minimize the end effect, the phase unbalance still exists, including both the amplitude and phase position unbalances. And the phase unbalances give rise to even order force ripple harmonics, in which the 2 ^nd -order force ripple is particularly significant. In order to compensate the end effect and the unbalance between the three phases, a novel PMLM topology is presented, in which the width of the two end teeth (instead of the edge teeth) is adjusted to reduce the force ripple. And the impact of the end teeth width on the ripple force magnitude is further revealed. It is shown that by proper design of the end teeth width, the 2 ^nd -order force ripple of the PMLM can be minimized to quite a low extent. In comparison with the original design, the 2 ^nd -order force ripple factor of the novel topology has been suppressed from 0.4% to less than 0.03% in the case study. Such a technique has provided a new way of force ripple minimization, and is applicable to other types of linear motors or actuators with appropriate changes.