Positional non-linearity compensation for electric motor

An iterative method for obtaining correction values for compensating positional non-linearity of a rotor of a synchronous electric motor, a single revolution of the rotor being divided into N mechanical positions, wherein the iterative method comprises:

• (1) controlling the electric motor to run at a constant speed based on a field-oriented control scheme, the field-oriented control scheme using a flux control signal that controls a magnetic flux in the electric motor;
• (2) determining, for each of i=1, . . . , N mechanical positions and for each of a predetermined number M of one or more revolutions of the rotor of electric motor running at the constant speed, one or more instantaneous flux control values using the field-oriented control scheme, wherein the instantaneous flux control values are based on respective position signals indicative of an absolute position of the rotor of the electric motor corresponding to the N mechanical positions and the predetermined number M of one or more revolutions;
• (3) filtering the instantaneous flux control values determined in step (2) for each of the N mechanical positions to obtain a respective filtered instantaneous flux control values Vd,i representing oscillation of the magnetic flux for each of the N mechanical positions;
• (4) multiplying the N filtered instantaneous flux control values Vd,i with a scaling factor;
• (5) updating correction values for an angular error of the rotor corresponding to the N mechanical positions in a compensation table based on the scaled and filtered instantaneous flux control values;
• and
• (6) repeating steps (2) to (5) using the updated correction values for an angular error of the rotor in the compensation table until reaching a predetermined number of iterations.