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

• Final Report Year: 2023

Final Report Abstract

This project has deals with magnetically levitated high-speed drives and so called “bearingless electric machines”. The given results are valid not only for certain industrial applications such as compressors, and they are also valid for higher power drives than the investigated power level. Magnetically levitated “bearingless motors” with cylindrical rotor do not need any radial magnetic bearing, but still require a separate axial active magnetic bearing to control the axial rotor position in case of an axial thrust. This magnetic bearing winding is fed in conventional drives with a DC current by a 4-quadrant chopper, requiring four power switches. In the proposed zero-sequence DC current feeding, the axial active magnetic bearing current is a star-point current, i. e. the sum of three zero-sequence currents of the three-phase motor winding. The feeding star points are available in any bearingless star-connected machine winding, but also non-electrical rotating machines, which are magnetically levitated via two 3- phase radial active magnetic bearings. The axial magnetic bearing voltage as a DC-voltage between the two star-points of the two motor half-windings is generated by modulation, i. e. by adding a DC-offset voltage to the two 3-phase AC reference voltages. Alternatively, an adapted space-vector pulse-width modulation may be used. With the zero-sequence current feeding, the four power switches of the 4-quadrant chopper are saved, thus reducing overall costs and the complexity of the system. This increases the attractiveness of the magnetic bearing technology. It is shown that the zero-sequence current feeding shows comparable dynamic position control behavior, compared to the classical 4-quadrant chopper feeding. Only at the inverter voltage limit, the zero-sequence current feeding leads to additional voltage harmonics in the axial active magnetic bearing voltage or in the 3-phase AC voltage of the bearingless machine. Using a modulation technique, which prioritizes one of both voltages, reduces the voltage harmonics of the prioritized voltage, however, at the costs of the nonprioritized voltage. Anyway, the resulting additional current harmonics are not crucial for a safe motor operation. The results are presented in a way, that the zero-sequence current feeding can be adopted in any modern power electronic inverter.

Publications

• “Bearingless PM synchronous machine with zero-sequence current driven star point-connected active magnetic thrust bearing,” in Transportation Systems and Technology 4 (1), 2018, pp. 5 … 18
  D. Dietz & A. Binder
  
• “Comparison between a bearingless PM motor with separated and combined winding for torque and lateral force generation,” in Proc. European Conference on Power Electronics (EPE), 2.-6.9.2019, Genova, Italy, 10 pages
  D. Dietz & A. Binder
  
• “Influence of PM-Material on the parameter uncertainty of Bearingless Synchronous Machines,” in Innovative Kleinantriebs- und Kleinmotorentechnik (IKMT), Würzburg, 10.-11.9.2019, ETG-Fachbericht 159, VDE-Verlag GmbH, Berlin, p.80-85
  D. Dietz & A. Binder
  
• Bearingless PM-synchronous machine with axial active magnetic bearing fed by zero-sequence current. e & i Elektrotechnik und Informationstechnik, 138(2), 62-69.
  Dietz, Daniel & Binder, Andreas
  
• Design Guidelines and Scaling Effects for Bearingless PM Synchronous Machines Accounting for Eddy Current Reaction Field. IEEE Transactions on Industry Applications, 57(6), 6844-6855.
  Dietz, Daniel & Binder, Andreas
  
• Eddy Current Influence on the Control Behavior of Bearingless PM Synchronous Machines. IEEE Transactions on Industry Applications, 57(6), 6944-6955.
  Dietz, Daniel & Binder, Andreas
  
• Operational constraints of zero-sequence current feeding in bearingless PM synchronous machines. e & i Elektrotechnik und Informationstechnik, 138(6), 383-393.
  Dietz, Daniel & Binder, Andreas
  
• “Bearingless PM Synchronous Machine with Axial Active Magnetic Bearing fed by a Zero-Sequence Current,” in More Drive Symp. 1.-2.9.2021, OVE, Vienna, Austria
  D. Dietz & A. Binder
  
• “Comparison Between NdFeB and SmCo5 Permanent Magnets Regarding Eddy Currents in Bearingless Synchronous Machines,” in International Symposium on Magnetic Bearings (ISMB), Online / Rio de Janeiro, Brazil, Aug. 2021.
  D. Dietz & A. Binder
  
• “Parasitic Effects of Magnetic Eccentricity in Bearingless PM Synchronous Machines,” in International Symposium on Magnetic Bearings (ISMB), Online / Rio de Janeiro, Brazil, Aug. 2021, 13 pages.
  D. Dietz & A. Binder
  
• “Design of a Bearingless Permanent Magnet Synchronous Machine with a Star Point-Connected Axial Active Magnetic Bearing”, 2022, TU Darmstadt
  D. Dietz
  
• “Indirect Efficiency Measurement and Levitation Property Determination for High-Speed Bearingless PM Synchronous Machines,” in Innovative Kleinantriebs- und Kleinmotorentechnik (IKMT), Linz, Österreich, 14-15.9.2022, GMM- Fachbericht 103, VDE-Verlag GmbH, Berlin, p.209-215
  D. Dietz & A. Binder