Re: what happen if external force make motor speed higher than expected speed in AN1078
While the considerations about the motor becoming a generator given above are a general truth, there's another option to slow such a motor down - provided it's not an asynchronous machine (of which I'm just not sure whether this recipe might work as well):
(Gradually) shorting the stator windings. This way, the excess power is dissipated in the stator windings (as opposed to being dissipated in some brake resistor). While this scheme is only applicable for short-term breaking and not-too-high energies, it virtually comes for free.
Not sure whether this concept comes readily with AN1078.
PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)