Comparison of Synchronous Machines with Neodymium and Ferrite Magnets for Electrical Traction Systems Manfred Schrödl, Univ.Prof. Dr.; Florian Demmelmayr, Dipl-Ing.; Bernhard Weiss, BSc; Markus Troyer Institute of Energy Systems and Electrical Drives, Vienna University of Technology
Costs of magnetic materials NdFeB (N40H): Ferrite (Y30): 70 /kg 2,17 /kg Cost development of Neodymium (Nd) [2] Cost development of Terbium (Tb) Dysprosium (Dy) [3] 12.12.2012 Manfred Schroedl / Florian Demmelmayr 2/24
Overview NdFeB and Ferrite - Machine Comparison of magnetic materials - Irreversible demagnetisation Performance comparison of both rotor variants Sensorless control Results 12.12.2012 Manfred Schroedl / Florian Demmelmayr 3/24
NdFeB and Ferrite - Machine Prototype of a traction motor Outer rotor motor wheel hub drive Tooth coil winding q = 0,4 Permanent magnets with flux contentration One stator two different rotors (Position-) Sensorless control NdFeB rotor lamination 12.12.2012 Manfred Schroedl / Florian Demmelmayr 4/24
NdFeB and Ferrite - Machine Stator NdFeB Ferrite 12.12.2012 Manfred Schroedl / Florian Demmelmayr 5/24
Overview NdFeB and Ferrite - Machine Comparison of magnetic materials - Irreversible demagnetisation Performance comparison of both rotor variants Sensorless control Results 12.12.2012 Manfred Schroedl / Florian Demmelmayr 6/24
Magnetic Circuit at Θ = 0 B M ( H M ) ~ h b M M 1 δ B δ, Ferrite = 1,47T B δ, NdFeB = 1,57T δ 12.12.2012 Manfred Schroedl / Florian Demmelmayr 7/24
Ferrite: Magnetic Circuit at Θ 0 12.12.2012 Manfred Schroedl / Florian Demmelmayr 8/24
Local irreversible demagnetisation Simulation of magnetic flux density in the ferrite magnets 12.12.2012 Manfred Schroedl / Florian Demmelmayr 9/24
Air gap flux density 12.12.2012 Manfred Schroedl / Florian Demmelmayr 10/24
Overview NdFeB and Ferrite - Machine Comparison of magnetic materials - Irreversible demagnetisation Performance comparison of both rotor variants Sensorless control Results 12.12.2012 Manfred Schroedl / Florian Demmelmayr 11/24
Induced no load voltage Measured no load voltage: Ferrite Simulation B r = 0,3T Ratio Û NdFeB / Û Ferrite 2 12.12.2012 Manfred Schroedl / Florian Demmelmayr 12/24
Efficiency in torque/speed plane NdFeB Ferrite 12.12.2012 Manfred Schroedl / Florian Demmelmayr 13/24
Comparison of rotor variants Simulation (Ferrite) Measurement (Ferrite) Measurement (NdFeB) Outer diameter (rotor) 50,4cm (+26%) 40cm Magnet volume 570% 100% Rotor mass 55kg 22kg max. short circuit current 45A 95A torque @ rated current 126,43Nm 118Nm (215Nm) Max torque at short circuit 28,6Nm 105Nm No load voltage 92% 100% 202% Efficiency < 92% < 94% 12.12.2012 Manfred Schroedl / Florian Demmelmayr 14/24
Overview NdFeB and Ferrite - Machine Comparison of magnetic materials - Irreversible demagnetisation Performance comparison of both rotor variants Sensorless control Results 12.12.2012 Manfred Schroedl / Florian Demmelmayr 15/24
Sensorless Control PM synchronous machines need: Knowledge on actual rotor position for control Position sensor - Costs for sensor and sensor electronics - Additional hardware components (higher failure risk) Sensorless methods Evaluation of anisotropic effects (INFORM) Evaluation of induced voltage (back EMF) Used method depends on actual rotor velocity INFORM Evaluation of different inductances in direct and quadrature axis (position-dependent inductances) : magnetic saturation Reluctance effect 12.12.2012 Manfred Schroedl / Florian Demmelmayr 16/24
Position-dependent Inductance NdFeB Ferrite Inductance depends on actual current operating point 180 ambiguity at low currents 12.12.2012 Manfred Schroedl / Florian Demmelmayr 17/24
Sensorless Control - INFORM Voltage steps Δi u u Messung der Phasenströme 2γ el INFORM-evaluation Elimimination of 180 ambiguity 12.12.2012 Manfred Schroedl / Florian Demmelmayr 18/24
Elimination of 180 ambiguity Large signal INFORM High currents (i s 1) Shifting the magnetic set point by test current Detection of the absolute electrical position High currents in ( d)- direction cannot be applied at ferrite machines Sector detection Detectionof thesign of d-axis Well-suited to ferrite machines 12.12.2012 Manfred Schroedl / Florian Demmelmayr 19/24
Quality of sensorless control Large signal INFORM NdFeB-Machine Standard deviation: 2,28 el Sector detection High reliability 12.12.2012 Manfred Schroedl / Florian Demmelmayr 20/24
Overview NdFeB and Ferrite - Machine Comparison of magnetic materials - Irreversible demagnetisation Performance comparison of both rotor variants Sensorless control Results 12.12.2012 Manfred Schroedl / Florian Demmelmayr 21/24
Results Important quantity for selection of magnet material:(bh) max (BH) max, NdFeB / (BH) max, Ferrite 12 Recommendation: Operating point B r /2 < B OP < B r This prevents from irreversible demagnetisation Ferrite magnets are not allowed to be operated at low flux density Nonlinear BH-curve in second quadrant Good capability for sensorless control The developed ferrite rotor has certain disadvantages for traction applications with respect to compactness However: it offers good efficiency 12.12.2012 Manfred Schroedl / Florian Demmelmayr 22/24
References [1] Weiss, Bernhard Vergleich von Permanentmagnet-Synchronmotoren mit Neodymund Ferritmagneten, Diplomarbeit, TU Wien, 2012 [2] Eriksson, Sandra; Bernhoff, Hans Rotor design for PM generators reflecting the unstable neodymium price, ICEM 2012, Marseille, France [3] Barcaro, Massimo; Bianchi, Nicola, Interior PM Machines using Ferrite to Substitute Rare-Earth Surface PM Machines, ICEM 2012, Marseille, France 12.12.2012 Manfred Schroedl / Florian Demmelmayr 23/24
Thank you for your attention!