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

A 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 the 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, the
$q$
-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 article, the influence of the
$d$
-axis HFSI on QEMF is investigated and compared with 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 the QEMF-based
$d$
-axis HFSI. The state observer and adaptive law are designed by a cascade methodology, which guarantees accurate extended electromotive force (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.