A Simple Search Coil Based on Motor Winding Strands for Rotor Position Estimation

Conventional sensors for detecting the rotor position in permanent magnet synchronous motors can be influenced by environmental conditions and may pose reliability concerns during operation. Accordingly, this study proposes a search coil design in which a single strand of the motor winding from each phase terminal is used to derive the three-phase stator flux linkage. The flux linkage is transformed into the alpha - beta frame to determine the stator flux linkage angle, which is then used to interrogate a pre-established lookup table to determine the corresponding motor rotor angle. The effectiveness of the proposed search coil is evaluated via experimental trials using a commercial 3.7-kW motor. The position estimation results are found to be in good agreement with those obtained using a commercial resolver under various speed and load conditions. The proposed search coil offers a simple, noninvasive, and reliable means of estimating the rotor angle. Importantly, the proposed search coil can function as either a reliable backup in the event of motor position sensor failure or as a primary sensor. It, thus, provides a suitable choice for a wide range of motor types.