Phase vector drives (or simply vector drives) are an improvement over variable frequency drives (VFDs)
in that they separate the calculations of magnetizing current and torque generating current.
These quantities are represented by phase vectors, and are combined to produce the driving phase vector
which in turn is decomposed into the driving components of the output stage. These calculations need
a fast microprocessor, typically a DSP device.
Unlike a VFD, a vector drive is a closed loop system. It takes feedback on rotor position and
phase currents. Rotor position can be obtained through an encoder, but is often sensed by the
reverse EMF generated on the motor leads.
In some configurations, a vector drive may be able to generate full rated motor torque at zero speed.