# What is the advantage of Interior permanent magnet over surface permanent magnet?



## tudole3 (Jan 25, 2017)

As tittle. I couldn't find much information to compare IPM to SPM. Does IPM supposed to have better torque control?


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## CoastalCruiser (Sep 29, 2017)

This has been discussed here and there. Can't find the core thread at the moment. Not 100% sure about one design having better torque control than another, but it may be the IPM motor. Reason being, most internal permanent magnet motors (in EVs) are used to augment a reluctance machine (switched reluctance motor), and electronics have been developed to precisely control reluctance machines.

Now that is torque _control_. For pure torque advantage, a motor builder told me once nothing beats a pure PM motor for torque. ;>

But comparing the designs in general, IPM designs use smaller magnets than PM designs, and combined with the very simple construction of the reluctance rotor are apparently cheaper to build.


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## PNWmisty (Aug 19, 2017)

I think the small magnets solve the problem of torque ripple (torque variation throughout the rotation of the motor) as well as increase efficiency.


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## tudole3 (Jan 25, 2017)

If the smaller magnet can reduce the weight, it will reduce the rotational inertia and increase efficiency.


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