Fixed Current Angle Operation Strategy in Low-Speed Sensorless Drive for Improved Torque Capability over Critical Point

This paper proposes a fixed current angle operation strategy in low-speed sensorless drive for improved torque capability of IPMSM. The operating principle of the proposed method and the effect of the critical point on the operating point would be analyzed. Based on the analysis, desirable location of the critical point for the proposed strategy to be effective is discussed. The proposed strategy has a simple control structure and can determine the d-q current references from an one-dimensional table without any additional LUTs for compensation. Analyses and experimental results verify that the actual current traces the MTPA trajectory less than 5 degrees of error bound and that torque capability has been improved from 1.75 p.u. to 2.4 p.u. by the proposed sensorless control method.