"Vector drive" is sales lingo for a motor that has been specifically designed to tolerate the spiky nature of VFD waveforms.
Cute, no?
Vector drive units don't have better torque -- per se -- they have their wiring -- especially the tap wires -- insulated to a wholly different, higher, standard than the normal NEMA stuff.
Once the windings have wrapped into the magnetic circuit/ taken a couple of laps around the silicon steel -- the magnetic field effects will have shaved off the highest spikes in the AC waveform.
From that point onward, even traditional winding insulation techniques will do fine.
The superior torque sales pitch is due to the fact that the VFD -- itself -- will adjust its frequency towards an idealized pull-in frequency during spool up.
This is to be contrasted with the common induction motor -- that starts out at zero rpms -- and 'sees' a rotating magnetic field racing away faster than the rotor could possibly catch up to. So, during spool up, it -- the rotor -- gets heated up -- and slips very, very, badly... particularly during high torque start-ups. (Traction motors, etc.)
The VFD slows the frequency down -- during the spool-up -- so that the speed of the revolving magnetic field is not so absurdly faster than the rotor.
A vector drive motor can tolerate this condition, too.
Slowing the spinning field down -- dropping the apparent frequency -- increases the delivered torque. (Inverse square law applies)
A VFD is brainy enough to spool up its waveform in tempo with the motor. Such pull-in/ spool up dynamics are adjustable in the field -- see the documentation provided with them.
Vector drive motors and mated VFD have almost entirely replaced DC traction motors. (!!!)
BART, most subways, the major railroads, etc. have all swapped out their DC systems for Vector 3-phase drive systems.
In the case of BART, it takes in 1000 VDC off of the third rail and uses it to power its 3 phase vector drive traction motors. The original power system (DC) was never changed.
It was in this fashion that both old style DC and new style AC could run side by side.
Otis Elevator has done the same thing for their product line. DC is out, vector drive is in.
