Optimal Design of Axial Flux Synchronous Machines With Coreless PCB Stator and Surface-Mounted or Halbach Array PM Rotors Considering Performance and Cost Objectives

This study systematically compares and examines two types of coreless printed circuit board (PCB) stator axial-flux permanent magnet (AFPM) machines for optimally designed cost-sensitive heating, ventilation, and air conditioning (HVAC) applications, differing in rotor configuration. The rotor topologies include conventional surface-mounted permanent magnet (PM) and Halbach array configurations. Analytical and finite element analysis (FEA) methods are employed to assess the air-gap flux density and torque capabilities of each rotor type within the same envelope. Both machines are then optimized using a combination of differential evolution and computationally efficient 3D FEA for the same rating and compared in terms of cost, weight, and efficiency. Optimization findings reveal that a Halbach array rotor coreless AFPM, with performance comparable to its surface PM counterpart, is lighter in mass yet significantly more expensive. A discussion is presented on AC loss mitigation in PCB stators, along with design considerations for coreless AFPM machines, including the effect of magnet-to-magnet gap on torque production and the role of the rotor back iron for the surface PM rotor and the non-magnetic supporting plate in the Halbach array rotor. Given the importance of cost sensitivity in the HVAC industry and based on a comprehensive analysis of production and operating costs, supported by validated analytical and FEA calculations, a prototype with a surface-mounted PM rotor was fabricated and experimentally tested.