Powertrain 2020 - The Future Drives Electric (PDF ... - Roland Berger

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For high-end applications, most car manufacturers use permanent magnet
synchronous motors (PMSMs). The main design difference between these
and induction motors is that PMSMs feature permanent magnets in the
rotor that generate the second magnetic field. This allows the rotor to rotate
at the same speed as the revolving magnetic field generated in the stator
(hence the "synchronous"). The entire supply current can be used to generate
the stator field, providing more torque per power input than induction
motors, especially at low motor speeds. PMSMs also have disadvantages,
however. These include higher production costs (due to the expensive
permanent magnets and more complex manufacturing process), lower
efficiency at higher speeds (due to undesired currents in the stator created
by the permanent magnets) and a high braking torque in case of short
circuit.