Forces in short-secondary linear reluctance motors

Short-secondary linear reluctance motors (LRMs) have applications in materials handling, particularly for drives through metallic containment barriers. A new theory is given for the normal force in an LRM, taking account of harmonics in the airgap field. The normal and tractive forces are expressed in terms of three geometrical coefficients Cd1, Cq1and Cq3obtained from a two-dimensional finite-element field solution. Force prediction in a short-primary LRM requires the coefficient values calculated for an infinite machine. Force prediction in a short-secondary LRM requires in addition the modified coefficient values for a single isolated segment. These two sets of coefficients permit the normal and tractive forces to be predicted with an accuracy of about 5% in a short-secondary LRM with any number of segments.