Design and control of a bearingless permanent magnet synchronous machine with a combined double-three-phase winding for torque and lateral force generation and star point-connected axial active magnetic bearing

• Applicant: Professor Dr.-Ing. Andreas Binder
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 437667923

The innovation:The novelty of the concept includes the integration of the axial active magnetic bearing supply into the inverter feeding of the bearingless motor for the sake of system cost reduction. In particular, the axial active magnetic bearing is connected between the two star-points of the bearingless motor stator winding, which is fed by a zero-sequence current. This feeds the axial magnetic bearing.Content of the project:The concept is realized on a 1 kW / 60000 rpm bearingless drive in order to investigate its operation limits. Critical influences are dentified and profoundly investigated. The prototype is (parametrically) designed, built and measured. The concept is also applied to higher power classes in simulation in oder to identify sizing effects. Comparisons between different power classes and with conventionally fed prototypes are made.Preparing work:The feasibility of the novel concept has been shown in principle and simulation. Some of the motor and inverter constraints, accompannied with the zero-sequence current, have been derived qualitatively. Moreover, the disturbing force due to eddy currents in the permanent magnets of the rotor have been discussed in theory. With this preliminary work the success of the project with regards to the research results is realistic.Aim of the project:For profound recognitions regarding limits of the application range for the concept, a fundamental design methodology, including scalability, and the realization in practice is essential. Only after explaining the practical recognitions in theory, a final validation of the concept is possible. This project closes exactly this gap, i.e. theoretical and practical investigation of the operation limits. In particular, the following questions are answered:a) How does the torque and suspension force ripple change for increased zero-sequence current and at higher power classes?b) How does the composition of losses change within the motor for increased zero-sequence current and at higher power classes?c) How much does the inverter switching frequency influence the dynamic of the axial position control and which conclusions can be drawn for IGBT-inverters of higher power classes?d) How much voltage reserve must be provided in the inverter for sufficient dynamic of the axial position control?e) Which winding topologies are suitable for bearingless motors with zero-sequence current feeding?f) To which extent has the stiffness of the radial position control to be increased in order to compensate for disturbing forces due to eddy current effects and which conclusions can be drawn for system control?g) From which electrical conductivity are massive permanent magnet materials inappropriate for bearingless machines and is this scalable for higher power classes?

• DFG Programme: Research Grants