Multilayer air gap winding designs for electric machines: theory, design, and characterisation

Abstract

Here, the authors present a magnetic circuit design with a multilayer air gap winding. This design provides a new degree of freedom in the design process. The approach is based on a single layer air gap winding, which demonstrates the ability to scale, permitting application in small and large electric machines. A meandering structure with coils arranged parallel to the rotation axis are mounted in several layers on a slotless magnetic core. The authors consider a fixed ohmic power loss boundary condition to compare this approach with an existing validated machine design. Machine current is reduced with each winding layer, while self-inductance and induced voltage are increased. Since the air gap height is increased with every additional layer, the useable magnetic flux density decreases. Accordingly, an utilisable range in which optimal torque output is obtained can be described analytically. The authors provide comparison between a single-layer winding design, which achieves the global optimum torque, and a four-layer winding design, which gives a 16-fold increase in the phase self-inductance. Additional thermal simulations prove that the multilayer design give the same ohmic power losses as the single layer design, without having any thermal issues and hot spots.

Keywords

• permanent magnet machines
• rotors
• coils
• air gaps
• permanent magnet motors
• torque control
• magnetic cores
• magnetic flux
• electric potential
• magnetic circuits
• machine windings
• finite element analysis
• torque
• fourfold increase
• torque-to-weight ratio
• ohmic power losses
• single layer design
• multilayer air gap
• magnetic circuit design
• 16-fold increase
• four-layer winding design
• global optimum torque
• single-layer winding design
• phase self-inductance
• torque ripple
• multilayer design
• torque-to-mass ratio
• optimal torque output
• useable magnetic flux density
• additional layer
• air gap height
• winding layer
• machine current
• existing validated machine design
• fixed ohmic power loss boundary condition
• magnetic poles
• meandering geometry
• slotless magnetic core
• meandering structure
• electric machines
• novel single layer air gap winding
• machine torque
• counter-electromotive force