Method for determining initial rotor position of permanent magnet synchronous motor according to phase current differences and line current differences and associated motor device

A motor device comprising:

• a permanent magnet synchronous motor (PMSM);
• and
• a processing circuit, coupled to the PMSM and arranged to:
• apply a plurality of voltages to each phase stator winding of a three phase stator winding of the PMSM, to obtain a plurality of transient currents from the PMSM;
• generate three phase current differences according to the plurality of transient currents;
• determine a first zone in which an initial rotor position of the PMSM is located according to the three phase current differences, wherein angles between 0-360 degrees are divided into a plurality of zones, and the first zone is selected from the plurality of zones;
• calculate three line current differences according to the three phase current differences;
• and
• determine a second zone in which the initial rotor position of the PMSM is located according to the first zone and the three line current differences, wherein the second zone is a portion of the first zone;
• determine a function value for the second zone according to two of the three line current differences;
• compare the function value with a threshold setting to generate a comparison result;
• and
• determine the initial rotor position of the PMSM according to the comparison result.