14PESGM2609 Wednesday, July, 30, 2014 1 Novel Single-Drive Bearingless Motor with Wide Magnetic Gap and High Passive Stiffness Hiroya Sugimoto Seiyu Tanaka Akira Chiba Tokyo Institute of Technology
1-1. Background Advantages of the bearingless motors No contact No wear No lubricant Non polluting Maintenance-free 1 Possible Applications Highly pure water pump in semiconductor industries High speed motor such as a compressor Cooling fan requiring long life-time Significant issues for industry application Bearingless pump http://www.levitronix.com/ Magnetic suspension cost is high! Thus, cost reduction is strongly required. Reducing number of active positioning axes is the most effective.
y x 1-2. A number of active positioning axes One-axis actively positioned bearingless motor can realie to reduce four active positioning axes. 5-axis active positioning 2-axis active positioning 1-axis active positioning y 1 x 1 y 2 x 2 2 Bearingless motor units Thrust magnetic bearing Bearingless motor Passive magnetic bearing Bearingless motor
1-3. Advantages of 1-axis bearingless motor 3 A single-drive bearingless motor is focused. The number of active positioning axes Required number of units six-igbt inverter four-igbt inverter 5 2 1 : Thrust magnetic bearing motor Sus.:2, Mot.:1 Sus.:1, Mot.:1 Mot.:1 1 : Single-drive bearingless motor Mot. & Sus.:1 Sus.:1 0 Sus.:1 0 displacement sensor 5 2 1 1 PM cost ratio $6 $6 $13 $13 Cost ratio 1 0.46 0.35 0.28 Single-drive bearingless motor needs only one threephase inverter and one displacement sensor for the suspension and motor regulations.
1-4. Single-drive bearingless motor concept 4 Two functions of the motor and the thrust magnetic bearing are magnetically integrated in the single motor. 1-axis magnetic bearing motor Controller Single-drive bearingless motor (SDBM) Controller 3-phase Inverter 1-phase Inverter 3-phase Inverter T F T Motor Thrust magnetic bearing F Beaingless motor with thrust magnetic bearing function
2. Purpose 5 Important issues in the single-drive bearingless motor are presented. A novel single-drive bearingless motor with wide magnetic gap and high passive stiffness is proposed. The 3D-FEM analyses and experiment results are presented.
Radial stiffness, k Radial stiffness, k r (N/mm) r (N/mm) 3-1. Important research issues 6 High passive stiffness for reducing vibrations in the radial and tilting directions Wide magnetic gap for centrifugal pump applications 40 40 30 30 20 20 10 10 Johannes Kepler Univ. in 2014 Calculated Measured Univ. of São National Taipei Paulo-USP Univ. of Tech. in 2009 Shiuoka Univ. in 2013 in 2011 00 0.0 0.1 0.2 0 Gap 0.1factor, g / R 0.2 Gap factor, g/r Proposed SDBM in 2013 Toyama Univ. in 2011
3-2. Proposed structure Increasing permanent magnets and the number of layers are effective to enhance the passive stiffness. 7 q RPMB SDBM Controller 3-phase Inverter i d*, i q * RPMB N S S N N S S N x y N S S N N S S N Hall sensor Winding Stator Rotor PM Displacement sensor
3-3. Requirement of the wide magnetic gap Plastic can must be installed on the rotor and stator surfaces to avoid the damage from chemical fluid. Outlet Passive magnetic bearing Rotor can Controller 3-phase Inverter Single-drive bearingless motor Passive magnetic bearing 8 Inlet x y Impeller Hall sensor Winding Stator Rotor permanent magnet Displacement sensor
3-4. Unstable thrust force 9 Active axial force to overcome the unstable thrust force must be generated for stable magnetic suspension. Controller RPMB SDBM 3-phase Inverter RPMB x y Hall sensor Winding Stator Rotor PM Displacement sensor
3-5. Initial idea of the SDBM structure 10 Active axial force is generated in one side of the coil-end by a shifting rotor in the axial direction. Structure (a) U Current direction Permanent magnet flux W V x y N S V W F,L N S f 10 U Coil-end 28
3-6. Active axial force in the initial structure Unfortunately, the axial force of Coil ends structure (a) is quite low. Several structures have been investigated. force, Axial suspension F force, suspension Axial (N) F (N) force, Fi (N) Active axial 1515 N F Rotor PM S 1010 Target Targetvalue value 6.28 7N N 55 00 (a) 00 11 22 33 ddaxis current, i (A) axis current, i d(a) d 44 55 11
3-7. Investigation of several structures 12 Structure (b) U W x V y N S V W F,L N S S N U Structure (c) Winding Current direction y q-axis d-axis N S x Stator core U-coil Rotor A Front F M N S B Permanent magnet flux Current direction Suspension flux Rotor F L N S U-coil Stator bars Stator yokes
Axial suspension force, F Axial suspension (N) force Active axial F i force, (N) F i (N) Continuous rating Twice 3-8. Principle of active axial force generation The active axial force is increased although structures (a) (c) can t achieve the target axial force. A novel structure without magnetic saturation is proposed. 15 10 15 10 5 0 5 0 0 Target value 6.28 N (d) (c) (b) (a) 1 2 3 4 5 0 1 2 3 4 5 d axis d axis current, current, i d i (A) d (A) 13
3-9. Proposed stator and rotor structures 14 The stator core is constructed with six bars. The rotor is two-pole cylindrical permanent magnet. The permanent magnet flux is distributed sinusoidal wave between the rotor and stator cores. Current direction Stator core y q-axis Winding Rotor S N x d-axis
3-10. Principle of active axial force generation 15 When the suspension flux is superimposed on the PM flux, flux density in the air-gap in positive -direction is high compared with that in negative -direction. Suspension flux Permanent magnet flux Flux strengthening Flux strengthening F N S Flux weakening Rotor Flux weakening Stator
3-11. Principle of torque generation 16 Virtual two-pole concentrated winding is generated by novel V-shaped winding structure. Fold angle f is key parameter for torque generation. Stator core q-axis V y Winding Current directions W d-axis i t i Stator core U U x f W V i t i i t Winding V-shaped winding structure
20 4-1. Test machine 17 Housing Windings Displacement sensor Prototype machine with the rotor and divided cores RPMB RPMB Two-pole PM Rotor PM RPMB RPMB Unit : cm PM for detecting angular position Rotor One of the divided cores with V-shaped winding
4-2. Demonstration movie 18 Rotor shaft
Current, i d, i q (A) Current, i d and i q (A) Axial displacement, (mm) Axial displacement, (mm) 4-3. Test machine 19 The rotor is served to the reference position after the d-axis current is excited. 0.3 0.3 Touch down length ±0.2 mm 0.2 0.2 0.1 0.1 0.0 0.0-0.1-0.1-0.2-0.2-0.3-0.3 4 0.00 4 0.02 Suspension 0.04 0.06 control is 0.08 activated 0.10 2 2 i d Time (s) 0 0-2 -2 i d = -2.98 A i q -4-4 0.00 0.00 0.02 0.04 0.06 0.08 0.10 0.10 Time Time (s) (s)
4-4. Test machine 20 The regulations of the axial position and the rotational speed are realied in the experiment. w (10 3 r/min) i d (A) (mm) 0.2 0.2 0.0 0.0-0.2-0.23 30.0 1.0 2.0 3.0 0-3 4000 0.0 1.0 2.0 3.0 2000 0 0-3 4 2 Static magnetic suspension ± 22 mm Acceleration up to 3600 r/min ± 0.95 A 3600 r/min 0 0 1 2 3 Time (s) 0.0 1.0 2.0 3.0
5. Conclusion 21 A novel single-drive bearingless motor with wide magnetic gap and high passive stiffness is proposed. Design process of the proposed single-drive bearingless motor is shown. In the experiments, stable magnetic suspension and speed regulations are confirmed.