Design and Analysis of a Magnetic-Spring-Enhanced Alternating-Pole Linear Motor for CO 2 Linear Compressors

This article proposes a magnetic-spring-enhanced alternating-pole linear motor (MSE-APLM) for carbon dioxide (CO2) linear compressors operating under high pressure differentials. The motor combines an alternating magnetization arrangement with an E-shaped stator to enhance the displacement sensitivity of the magnetic circuit, producing an inherent nonlinear magnetic spring characteristic. An equivalent magnetic circuit model is developed to analytically explain the origin of the magnetic spring stiffness and its displacement-dependent behavior. A 3-D finite element model, validated against experimental measurements on a Redlich-type prototype, is used to evaluate the proposed design. Under identical copper usage, the optimized MSE-APLM (Lₚₘ=19mm,δ g =0.9mm) achieves a peak thrust of 137.3 N—comparable to the Redlich-type motor—while delivering3.99×and2.88×the magnetic spring stiffness of the Redlich-type baseline in the small- and large-displacement regions, respectively. The alternating-pole configuration additionally generates attractive inter-magnet forces, improving assembly scalability.