Interdisciplinary Design of a High-Speed Drivetrain for a Kinetic Compressor in a Higherature Heat Pump

Abstract

Bearingless motor (BLM) technology offers a competitive solution to active magnetic bearings (AMBs) in high-speed applications. A bearingless drivetrain (BLDT) working as part of a kinetic compressor in a heat pump exceeding 0.5 MW and 25 000 rpm is open for questions: how should the geometry, materials, and parameters be chosen without exceeding the electromechanical and thermal limits; what rotor configuration would suit the heat pump; and how can the working fluid of the heat pump be used in the motor cooling? This paper presents the interdisciplinary design process of a BLDT as part of the compressor of a higherature heat pump (HTHP). The motor design process-the motor constituting the core driving the compressor of the heat pump, each interacting with the others, thus bringing about various design challenges-is summarized in a flowchart and subsequently elaborated on. Dimensioning rules for the bearingless structures are presented. Finite element analysis (FEA) is used to evaluate the surface and interior permanent magnet BLM structures under consideration. Different stack materials are considered and preliminary electromechanical optimization by a genetic algorithm is carried out. To ensure structural rigidity, FEA of electromagnetic, mechanical, thermal, and rotor dynamic performance is conducted. FEA of drive losses is carried out and cooling alternatives are considered, based on which temperature distributions and thermal stresses with the chosen cooling arrangements are calculated again with FEA. The power and performance of the structures are discussed. As a result of the analyses, a suitable hermetic motor design is chosen for the HTHP compressor drivetrain.