High-Frequency Voltage Injection for Synchronous Reluctance Motor under Magnetic and Cross-Coupling Saturations

In sensorless field-oriented control (FOC) of synchronous reluctance motors (SynRMs), high-frequency voltage injection (HFVI) is widely employed. However, the HF current response in this injection is significantly affected by magnetic and cross-coupling saturations. Magnetic saturation causes substantial variations in parameters such as flux and inductance depending on the amount of current, leading to nonlinear characteristics in the HF current response. Meanwhile, cross-coupling saturation results in mutual coupling between the dq-axis currents, introducing error components, such as offset, into the current response. These effects can significantly degrade the accuracy of position estimation based on HFVI. To address these issues, a HF current response model was developed in this study based on theoretical analysis and finite element method (FEM)-based electromagnetic simulations, with consideration of cross-coupling saturation. Using the developed model, the influences of magnetic and cross-coupling saturations on the HF current response were analyzed, and a method is proposed that combines two HF current responses along the dq-axis. The validity of the proposed model was verified by comparing its characteristics with experimental results obtained using a 2.2-kW-class SynRM. Finally, the effectiveness of the proposed method was demonstrated through experimental validation using a motor drive platform.