"Required" is a really strong word here. In practice when you have FF in the gap area, then even under what I would call heavy loading situations the motor core is typically not going to get more than like 70-80 oC, the shell and magnets of course even cooler still, and that's way below the point where demagnetization even with field weakening currents would be of concern. If you're using the fact that there is FF in order to dump much more power into the motor core than you would otherwise do, then yes that would result in hotter magnets and you'd be prudent to have a temp sensor and do thermal rollback as always.jmz wrote: The net effect is that I believe extremely good thermal bonding of the magnets and rotor backing to the shell will be required if field weakening is to be employed while increasing heat transfer through the rotor, hence potting of the rotor up to and perhaps over the magnet surfaces will be required when using FF.
As has been said before, if you put the same input power in a motor with and without FF, the final steady state shell and magnet temperatures will be quite similar, even though the core in the non-FF case is much hotter. It's only during the transient stage as things are warming up that the motor with FF will show warmer magnets and casing.