The brushless DC motor combines many of the advantages of the permanent excited DC motor and the synchronous motor. It has no exciting losses, and no wear out. The brushless DC motor needs low reactive current, so similar to the DC motor, the current is proportional to the torque. Measuring the shaft torque is therefore easy to realize by detecting the DC current in the DC link. High supply voltage is allowed - only limited by the power transistors in the frequency inverter and the winding insulation of the motor.
Like the DC motor, the brushless DC motor needs a speed control and a speed sensor. Like the synchronous motor it needs its own frequency inverter.