Analysis and Suppression of Phase Unbalance Induced Force Ripples in Permanent Magnet Linear Motors

Abstract

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.

Direct Thrust Force Fault-Tolerant Control of Primary Permanent Magnet Linear Motor With Single DC-Link Current Sensor for Metro Application

“…As a result of high power density, small size and light weight, permanent magnet linear motors (PMLMs) are get more and more concerns [5][6][7]. Meanwhile, PMLMs with unique merits are widely used in various industries [8][9]. However, in urban rail transit long-distance transportation systems, the high engineering cost and difficult maintenance in the later period must be lead into, whether the permanent magnets (PM) or armature windings is laid on the track.…”

Optimization Design of Thrust Characteristics of Switched Flux Linear Motor

“…In Ref. [18], taking the PMLSM as an example, it is proposed that the second‐order force ripple caused by phase imbalance can be effectively suppressed by properly changing the end teeth width. In Ref.…”