Full‑speed sensorless control of HEAFSPMM using nonlinear adaptive flux observer, improved MRAS, and ADRC speed controller

This paper proposes a low-noise, full-speed sensorless control strategy for a hybrid excitation axial flux-switching permanent magnet machine (HEAFSPMM). To eliminate the acoustic noise and additional losses inherent in conventional high-frequency signal injection methods, a nonlinear adaptive flux observer with saturation-based sliding correction and a disturbance observer is developed for zero- and low-speed operation without any dedicated high-frequency carrier signal; instead, the inherent current ripple from the PWM inverter naturally satisfies the persistence of excitation condition. For medium and high speeds, an improved model reference adaptive system (MRAS) that incorporates the excitation winding current i f is employed, enhancing estimation accuracy under heavy load. A sigmoid weighting function provides a bumpless transfer between the two observers. Furthermore, an active disturbance rejection control (ADRC) speed controller replaces the conventional PI controller, consisting of a third-order extended state observer and a nonlinear state error feedback law. Lyapunov-based stability analysis proves uniform ultimate boundedness of the flux observer, asymptotic stability of the MRAS, and practical stability of the switched system. Experimental results on a 600-W HEAFSPMM prototype validate the proposed method: the low-speed position error remains below 2.5º with no injection ripple, the sigmoid transition reduces the error spike from 4.5º(linear weighting) to 2º, the torque ripple is reduced by 55–63% across the full speed range, and the speed drop under load steps is reduced by more than 60% compared to the HF-injection+MRAS hybrid. The proposed method achieves silent operation, negligible extra losses, and superior robustness, making it an attractive solution for electric vehicle and industrial drives—without requiring any dedicated injected signal.