A Novel High-Frequency Injection Method Towards Speed-Sensorless Drive Control of Induction Machines over Full Speed Range

This paper proposes a systematic procedure to enhance the torque capability of sensorless induction machine control at/near zero frequency/speed under high-frequency signal injection (HFSI). The key idea is to select the tilted injection angle by two criteria: (1) maintaining the polarity of the sensitivity of an error signal w.r.t. the rotor flux angle estimation error to ensure closed-loop stability, and (2) maximizing the sensitivity to ensure robustness against uncertainties. Three look-up tables of injection angles and error scalings are constructed regarding operating points and used for real-time HFSI implementation. We further integrate the proposed HFSI method with an adaptive flux observer to enable a stable sensorless torque control at full-speed range. Experimental results validate the torque capability and demonstrate smooth operation over the full speed range of the proposed unified observer.