AN ANALYTICAL METHOD FOR THE CALCULATION OF STATIC CHARACTERISTICS OFLINEAR STEP MOTORS FOR CONTROL ROD DRIVES IN NUCLEAR-REACTORS

An analytical method for calculating static characteristics of linear dc step motors (LSM) is described. These multiphase passive-armature m otors are now being developed for control rod drives (CRD) in large nu clear reactors. The static characteristics of such LSM is defined by t he variation of electromagnetic force with armature displacement and i t determines motor performance in its standing and dynamic modes of op eration. The proposed analytical technique for calculating this charac teristic is based on the permeance analysis method applied to phase ma gnetic circuits of LSM. Reluctances of various parts of phase magnetic circuit is calculated analytically by assuming probable flux paths an d by taking into account complex nature of magnetic field distribution in it. For given armature positions stator and armature iron saturati ons are taken into account by an efficient iterative algorithm which g ives fast convergence. The method is validated by comparing theoretica l results with experimental ones which shows satisfactory agreement fo r small stator currents and weak iron saturation.