Comparison of PM-machines with ferrite and NdFeB magnets in terms of machine performance and sensorless start-up control

Abstract

The costs of rare-earth permanent magnets such as NdFeB increased rapidly in the last few years. Therefore, great attention is paid for alternative magnet materials. This paper compares two permanent magnet synchronous machines using external rotors with different magnet materials -one with NdFeB and the other with much cheaper ferrite magnets. The first section examines the risk of irreversible demagnetization of the ferrite magnets at inappropriate operating points. Furthermore, measurements and some numerical-simulation results contrast characteristics of the machines in terms of no-load voltage, shortcircuit behavior, torque output and efficiency. Different magnet materials influence position-sensorless techniques based on anisotropic effects especially for start-up control. The last part of this study compares two methods to estimate the absolute electrical rotor position at standstill. Reliability considerations show their quality at the respective machine.

Design and analysis of a highly integrated 9-phase drivetrain for EV applications

“…Hence it is necessary to derive rotor designs with a larger amount of magnets to achieve a performance level equal to conventional NdFeB ones [22], [23], [24], [26]. This became a challenging part since neither the magnets nor the electrical steel sheets are characterized by high mechanical strengths.…”

Analytic calculation of magnetic field and electromagnetic performances of spoke type IPM topologies with auxiliary magnets

“…The Poisson's equation in subdomain region IV where the relative recoil permeability is equal to 1 is given by 2 2 , , ,…”

On the relation between performance and permanent demagnetisation in spoke type machines with ferrite magnets

“…In previous studies, the access of permanent demagnetisation on the PMs is done only on the final design, excluding this constraint from the design algorithm [8][9][10], that is, demagnetisation consideration is not integrated in the design process. Also, in others, the demagnetisation is only accessed using three fixed levels of current for fault conditions, ignoring the influence of the magnetic circuit on the amplitude of the fault current [11].…”

“…The novel methodology of completely integrating the demagnetisation into the optimisation process allows the evaluation of its impact on the machine design and performance. In contrast to the common demagnetisation check on a final design, sometimes leading to re-design [8][9][10]. The method used to access the partial permanent demagnetisation effects by considering the recoil behaviour is similar to the one proposed in [14].…”