Fractional-Order Quasi-Resonant Extended State Observer for Position Error Compensation in PMSM Sensorless Control

Flux linkage observers have been widely employed in permanent magnet synchronous motor (PMSM) sensorless drives, and the back electromotive force (BEMF) estimated by an extended state observer (ESO) can be used to compensate for the position estimation error of the flux linkage observer. However, inverter dead time introduces periodic disturbances into the estimated synchronous reference frame, thereby contaminating the BEMF estimation and degrading the accuracy of position compensation. To this end, a position estimation error compensation strategy based on a fractional-order quasi-resonant extended state observer (FOQR-ESO) is proposed. First, a PMSM voltage model incorporating the inverter dead-time effect is established, and the resulting sixth-order harmonic component in the estimated synchronous reference frame is analyzed. Then, a fractional-order quasi-resonant element is embedded into the ESO to enhance its capability to estimate harmonic components. The proposed FOQR-ESO separates the BEMF-related component from the sixth-order harmonic disturbance, while the fractional-order parameter provides an additional degree of freedom for shaping the observer frequency response. Simulation and experimental results demonstrate that the proposed FOQR-ESO effectively suppresses the sixth-order harmonic disturbance and achieves higher rotor position estimation accuracy than the conventional ESO and the integer-order quasi-resonant extended state observer (IOQR-ESO).