Direct Torque Control (DTC) is a patented ABB technology that provides exceptionally good sensorless vector control of induction motors. The improvements come primarily because of the quality of the motor model which is constructed in drive memory when commissioning the system. It is not uncommon to acheive .1% speed regulation without an encoder with DTC.
The system is also very fast which allows the torque response of the motor to follow step changes in the speed reference with nearly servo performance. As with most AC drives, positioning is not possible as with servo systems unless a separate positioning controller is added.
Having said that, none of these benefits may be worth anything in your application. So, as always, you need to understand your load's requirements and build your power-train, motor, and drive to match.
One of the unusual aspects of DTC is that there is no PWM carrier. The drive issues power pulses to the motor based on rotor position, torque demand, and speed. For the purpose of spec'ing reactors, etc. an approximation of carrier frequency is 3.16khz.
I don't see why DTC drives need to be double in price. I am an ABB territory manager in Michigan USA and our pricing is right in line with other higher performance drive systems.
