High-Performance Low-Cost Electric Motor for Electric Vehicles Using Ferrite Magnets

Abstract

Permanent magnet motors with rare earth magnets are amongst the best candidates for high performance applications such as automotive. However, due to their cost and risks relating to security of supply, alternative solutions such as ferrite magnets have recently become popular. In this paper the two major design challenges of using ferrite magnets for a high torque density and high speed application, namely their low remanent flux density and low coercivity, are addressed. It is shown that a spoke type design utilizing a distributed winding may overcome the torque density challenge due to a simultaneous flux concentration and reluctance torque possibility. Furthermore, the demagnetization challenge can be overcome through careful optimization of the rotor structure, with the inclusion of non-magnetic voids on the top and bottom of the magnets. To meet the challenges of the high speed operation an extensive rotor structural analysis has been undertaken, during which electro-magnetics as well as manufacturing tolerances are taken into account. The electromagnetic studies are validated through testing of a prototype, custom built for static torque and demagnetization evaluation. The disclosed motor design surpasses the state of the art performance and cost, merging the theories into a multi-disciplinary product.

Shaft cooling and the influence on the electromagnetic performance of traction motors

“…In this case, based on the CFD results, the shaft hole average heat transfer coefficient can be correlated with the rotational speed. Application of the concept to a Ferrite magnet based tarction motor Using the Template A ferrite magnet motor design, [20], is used to verify the benefits of the shaft-cooling approach on the electromagnetic and thermal performance. An experimental investigation was carried out with 50-50 ethylene glycol-water as a shaftcooling coolant under various operating conditions.…”

Roles of coercivity and remanent flux density of permanent magnet in interior permanent magnet synchronous motor (IPMSM) performance for electric vehicle applications

“…[1][2][3] The performance of IPMSM is strongly affected by magnetic properties of the permanent magnet (PM), such as remanent flux density (B r ) and coercivity (H c ). Therefore, selection of PM is an important factor in motor design.…”

Demagnetization investigation of a partitioned rotor flux switching machine with hybrid permanent magnet

“…[4][5][6] Especially when traction machines operate under extreme conditions, such as overload and deep flux-weakening, the PMs suffer from high irreversible demagnetization risk. [7][8][9][10] In this condition, the output torque capability will be reduced to some extent, which impacts the continuous high-reliability operation of the vehicles. However, during the design process of the conventional PM machines, the anti-demagnetization investigations of the PMs are often ignored.…”

“…[7][8][9][10] In the Ref. 6, the demagnetization characteristics of the PM-assisted synchronous reluctance motor are investigated under different current loads, revealing that the PM is demagnetized seriously when 2.5 times rated current is fed.…”