In Chapter 3 we observed that the thrust/kVA and thrust/loss ratios for linear induction actuators (LIAs) are rather low. On the other hand, in Chapter 4 we concluded that these ratios are high for linear permanent magnet synchronous actuators (LPMSAs). These are relatively expensive, however, owing to the costs of magnets. Recent research in rotary reluctance machines has led to the development of linear reluctance synchronous actuators (LRSAs), which are relatively inexpensive and have good performance indices. Most LRSAs correspond to their rotary counterparts, including reluctance motors with traveling fields, switched reluctance motors, stepper motors, etc. LRSAs are especially suited for low-speed (less than 2 m/s) applications.

In analyzing an LRSA, it is to be noted that the winding concepts and details of LIAs (Chapter 3) are valid for LRSAs, and its speed being low, end effects in an LRSA may be neglected. However, the presence of high saliency on its secondary must be taken into account. In essence, theory pertaining to rotary reluctance motors is also applicable to LRSAs, except for the existence of normal forces in the latter, which merits special treatment.

PRACTICAL CONFIGURATIONS AND SALIENCY COEFFICIENTS

Like most linear electric actuators, LRSAs may be tubular or flat, single-sided or double-sided, with the secondary as the mover. The primary windings are three-phase ac windings as in LIAs. The secondary should have a high saliency.