Force Ripple Reduction of a Fractional Pole Pair Complementary Modularized Variable Reluctance Linear Machine for Long Stroke Application

Variable reluctance linear machine (VRLM), which takes advantage of magnet-free, simple structure, and low cost, is one of the emerging candidates for long stroke application. However, due to the abundant harmonics in the air gap, the conventional modular linear machine suffered from thrust ripple, which leads to vibration and acoustic noise problems. The thrust force ripple in VRLM is mainly caused by higher order harmonics in the induced voltage and detent force. To furtherly suppress the odd-order harmonics in the induced voltage and detent force, a fractional pole pair unequal module arrangement (FP-UMA) design, in which the distances of adjacent modularized mover segments are not equal, is proposed to VRLM and collaborated with complementary structure in this article. The key is that the modularized movers are artificially designed to be unequally distributed regarding spatial distribution to eliminate the odd-order harmonics in the induced voltage along with the thrust ripples that they caused based on the quantitative analysis of the thrust ripple components. It is revealed that, with the proposed FP-UMA design, the thrust ripple ratio of the machine has been effectively relieved from 4.6% to 2.2% under copper loss of 450 W. Furthermore, some design guidelines for the proposed machine, such as position offset of modularized mover $\Delta \lambda _{m2}$ , dc loss ratio $k_{\mathrm {dc}}$ , and slot pole combinations, are discussed. In addition, the feasibility of the proposed design method is evaluated by the finite element method and experiments.