A Sensorless Permanent Magnet Synchronous Motor Drive with Full Range Speed and Position Control using Feed Forward Torque Control

Feed Forward Torque Control (FFTC) is a totally new technique for sensorless control of the PMSM which uses none of the existing methods or technology. It approaches the sensorless control problem from completely different way which has never been considered in previous research.

All previous methods, except the stepper motor, are based around estimating the rotor position from motor terminal measurements instead of measuring it directly. FFTC uses the reverse of this process. FFTC starts with the required motor torque then calculates the wanted motor position from a model of the load and the required motor voltages from an inverted model of the motor (which converts motor currents to voltages instead of voltages to currents). Errors between the rotor position applied to the motor and the actual rotor position are corrected at high speed by using the error in the motor currents to correct the load model and at low speed by increasing the motor current in the correct phase sequence to lock in the rotor position, similar to a stepping motor. Standard speed and position feedback loops are easily applied to the feed forward torque controller for the control of speed or position.

FFTC offers many advantages over the sensorless control techniques currently being used:

·         Only one method is required to operate over the full speed, including fast speed reversals and zero speed operation under load.

·         It does not require any specially designed motors.

·         Existing methods use high bandwidth current feedback loops which need high computing power. FFTC uses very low bandwidth current feedback greatly reducing the needed hardware computing resources.

·         The problem of extracting the rotor speed and position information from the motor terminal voltages and currents is removed.

·         The problem of estimating the motor resistance with varying motor temperature is removed. FFTC does not require accurate knowledge of the motor resistance to operate.

·         Existing methods use feed-back torque control, resulting in a delayed torque response. Torque response with FFTC is instantaneous, allowing much faster response times for servo applications.

FFTC is not only applicable to the PMSM. It can be applied to all other AC motors including the induction motor. With the induction motor, FFTC can provide significant improvements over existing sensorless control methods.

Detailed information about FFTC can be found by following the links below. Details of some recent advances are limited due to confidentiality constraints. If you require more information, please contact me.

  1. FFTC White Paper.pdf Brief introduction to Feed Forward Torque Control.

  2. FFTC Description March 2018.pdf Newest version including flux weakening and improved damping and speed control.

  3. FFTC Description.pdf Old version, but more detailed.

  4. Video presentation of FFTC applied to a hybrid stepper motor (YouTube link)

  5. Video demonstration of the sensorless PMSM controller (YouTube link)