Hi,
High speed means high frequency.
But high frequency means loss (heating) in the magnetic core.
The higher the frequency, the higher the loss.
There's a dilemma.
If you simply "switch" the power, then this will cause overtones.
These overtones are useless for rotation, but cause a lot of heating because of their high frequency nature.
An ideal waveform is a pure sine, it has no overtones.
Therefore the use of overtone filters (LPF) you may be able to improve speed.
The drawback is, that it also reduces voltage and introduces phase shift. You have to take care about both.
Klaus