Comparison of torque responses of the interior permanent magnet motor under PWM current and direct torque controls

This paper compares the conventional CRPWM torque control scheme (in the rotor reference frame) for interior PM synchronous motor drives with the direct torque control scheme which operates in the stator reference frame. The direct torque control scheme, controls the stator flux vector directly in the stator reference frame as a means to control torque. It has several advantages such as elimination of the mandatory rotor position sensor, stator to rotor transformation and closed-loop PWM current controller networks/software. The elimination of certain hardware/software and of the inevitable delays inherent in these networks potentially results in a much faster dynamic torque response than that which is obtained with PWM current control. This paper examines the response times of torque for the two schemes through analysis, modelling and experimental studies, and compares the two strategies of torque control.