A Sensorless Permanent Magnet Synchronous Motor Drive with Full Range Speed and Position Control using Feed Forward Control
Feed Forward Control (FFC), and its predecessor Feed Forward Torque Control (FFTC), is a new technique for sensorless control of the permanent magnet synchronous motor which offers greatly improved performance over existing methods.
As its name suggests, FFC uses direct feed forward methods to control the motor. When operating in speed control mode, both phase and amplitude of the output voltages applied to the motor together with an applied rotor position are directly controlled by the speed command input. When operating in torque control mode, the controller switches from direct control by the speed command to direct control by the torque command. With the motor currents no longer needed for an output current controller, as used in traditional field oriented control, they are used instead to provide motor damping and to modify the feed forward transfer functions to adapt to changing loads which ensures the rotor stays locked in position.
The result is a sinusoidal output motor controller with almost instantaneous speed response with no overshoot, even at and through zero speed, with no position sensing required. It has no current loops, allowing it to operate at very high speeds, with output voltages up to the DC supply voltage, and even higher with over-modulation.
Feed forward control of a motor is not a new control method. Traditional induction motor V/F control is a direct feed forward control method with the output voltage and speed being directly controlled by the input speed command. FFC for permanent magnet motors was developed from this by adding precise voltage amplitude and phase control with the aid of current feedback adjustments.
With the aim of illustrating FFC for the speed control of drone motors, a prototype drone-motor speed controller has been developed.
The prototype has been designed to control a quad-copter motor suitable for driving a 5 inch propeller.
The operating manual for the prototype can be found here (man.pdf).
A book describing in detail how FFC work with application to a drone motor can be found here (book.zip).
A video introducing FFC and its basic operation applied to the prototype controller can be found here (intro.mp4).
A video showing how to tune the prototype controller to a motor is shown here (tuning.mp4).
A video showing the prototype controller’s performance can be found here (tests.mp4).