In-Depth Study of the Torque Constant for Permanent-Magnet Machines

The torque constant, together with the back-EMF constant, was originally used in permanent-magnet DC commutator (PMDC) motors to couple electric circuit equations with mechanical equations. It is still an open question how these two constants should be defined in brushless DC (BLDC) motors and permanent-magnet (PM) AC motors. We present an in-depth study of these two constants, and conclude that the definition based on thedqaxes is applicable for the dynamic motion control of not only PM AC motors, but also BLDC motors.