Study of the materials and thermal aspects of a BLDC motor with flexible PCB windings for submersible or high temperature and humidity applications

Current electrical machines are extremely efficient thanks to the continuously brought improvements. Lately, the emergence of the flex-PCB technology for the BLDC motor windings further increased their performances. These machines are now more often used in particular conditions, notably submarine exploration or medical surgery assistance. In this last application, hygiene is primordial, therefore sterilisation cycles might become the daily treatment of the motors. Their design in these particular conditions is much more challenging than in more classical ones. Indeed, some critical parts of the motor such as the windings, ball bearings or magnets might face severe degradation under these harsh conditions. Therefore, one goal of this thesis is to provide a description of the impact of these conditions on the different parts, thanks to both existing solutions reviewing and experimental testing. Submersible operation being very harsh for the materials, it still brings benefits regarding the thermal management of the machine. The other main goal of this work is to develop a thermal model highlighting the advantages and drawbacks of these operating conditions. This model will amongst others allow to describe the trade-off existing between the better heat dissipation increasing the maximum output torque of the machine, and the bigger friction forces thus reducing its efficiency in submersible operation. The final aim of this thesis is not to develop a submersible or sterilisable motor, but rather to describe the challenges that such motors generate for the design process.