Effects of d-Axis Inductance Change for Position Sensorless Control of SynRM at Low Velocities by Using an Extended EMF Caused by High-Frequency Current Superposition

Synchronous reluctance motors (SynRMs) are notable for lacking magnets or and rotor windings. For control of torque of SynRMs, information about position of rotor is essential; however, sensorless control is preferred for improved reliability, cost reduction, and space saving. This approach is challenging at low velocities due to the reduced electromotive force from the flux. We proposed a position-estimation method using the SynRM model to estimate the high-frequency extended EMF (HF - EEMF), including position information, by superimposing small high-frequency (HF) currents using SynRM. The SynRM's inductance changed significantly based on the load. We discussed how the influence between the setting value and the actual value of the d-axis inductance in the SynRM model affected this position estimation method, and experiments verified its influence. Additionally, we introduced a method to measure the actual value of the d-axis inductance using experimental result. The proposed method was verified experimentally.