Study on QEMF Model and Adaptive Full-Order Observer Design for Universal Sensorless Control of IPMSMs

Abstract

Quadratic extended electromotive force (QEMF) model enabled the use of traditional high-speed adaptive estimation methods combined to high-frequency signal injection (HFSI) for full-range sensorless position control of interior permanent magnet synchronous motors (IPMSMs). However, the first QEMF model presented in literature only works with HFSI in the q-axis, due to the QEMF being a function of the q-axis current derivative. The q-axis HFSI is known to produce undesired torque ripple. Furthermore, q-axis signal injection can be insufficient for low-speed position estimation in IPMSMs with low salience. A recent study demonstrated that the QEMF concept can be modeled as a function of the d-axis current derivative. In this paper, the influence of d-axis HFSI on QEMF is investigated and compared to the q-axis HFSI method. Furthermore, the electromotive force based observers are usually designed for medium to high-speed operation. Here, the adaptive full-order observer is adapted in order to achieve universal sensorless control through QEMF based d-axis HFSI. The state observer and adaptive law are designed by a cascade methodology, which guarantees accurate EEMF estimation and robustness throughout the entire operating speed range. Experimental results are presented in order to validate the proposed method and analysis under full-range sensorless control.