Abstract
In this paper, the partitioned rotor flux switching permanent magnet machine with ferrite permanent magnet is proposed. By the adoption of the partitioned rotor configuration, the stator flux leakage is eliminated and the permanent magnet utilization is improved. The ferrite permanent magnet machine often suffers from irreversible demagnetization due to the inherent relatively low coercivity of ferrite permanent magnet. To mitigate the machine irreversible demagnetization risk, an improved partitioned rotor flux switching permanent magnet machine with hybrid permanent magnet topology is also proposed. Two little pieces of rare-earth permanent magnet are installed at the corners of ferrite permanent magnet, thus forming the hybrid permanent magnet topology. And the demagnetization mechanisms of both machines are clarified by the magnetic equivalent circuit method, which prove that the rare-earth permanent magnet offer magnetic protection function for the ferrite permanent magnet. Furthermore, by the 2-D finite element analysis, the demagnetization characteristics and the electromagnetic performances of the two machines are quantitively assessed, revealing that the demagnetization risk is reduced significantly. Both theoretical analysis and simulation results verify that the improved machine can not only maintain low-cost design, but also possess enhanced demagnetization withstand capability and competitive electromagnetic performances as expected.
Highlights
Rare-earth permanent magnet (PM) machines have been widely applied in electric vehicles (EV) and hybrid electric vehicles (HEV) where high power density and high energy efficiency are required.[1,2,3]
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 improved partitioned rotor flux-switching permanent magnet (PR-FSPM) machine, the flux densities of all seven different locations in the FPM are above the demagnetization limit during operating process
Summary
Rare-earth permanent magnet (PM) machines have been widely applied in electric vehicles (EV) and hybrid electric vehicles (HEV) where high power density and high energy efficiency are required.[1,2,3] With the increasingly strict operating environments for traction machines, highreliability operation of machines has gained much attention.[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. A new ferrite PM topology is proposed in Ref. 20 to mitigate the PM demagnetization risk, the machine can sustain irreversible demagnetization even under five times the rated current. In contrary, this kind of machines still suffer limited torque density and serious outer flux leakage. By incorporating the concept of partitioned rotor and non-rare-earth PM, the partitioned rotor flux-switching permanent magnet (PR-FSPM) machine with ferrite PM is proposed The novelty of this machine is that by the adoption of partitioned rotor, the stator flux leakage can be avoided and the PM utilization can be improved. This paper propose a new orientation for utilizing ferrite PM, in which desired torque density and augmented demagnetization withstand capability can be realized at the same time
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