Electrical & Computer Engineering, Department of


Date of this Version

Spring 4-2014

Document Type



Y. Zhao, “Position/Speed Sensorless Control for Permanent-Magnet Synchronous Machines,” Ph.D. dissertation, Dept. Elect. Eng., University of Nebraska, Lincoln, NE, 2014.


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Electrical Engineering, Under the Supervision of Professor Wei Qiao. Lincoln, Nebraska: May, 2014

Copyright (c) 2014 Yue Zhao


Permanent-magnet synchronous machines (PMSMs) are widely used in industrial applications owing to their distinctive advantages, such as high efficiency, high power density, and wide constant power region. To achieve high-performance field oriented control, accurate rotor position information, which is usually measured by rotary encoders or resolvers, is indispensable. However, the use of these sensors increases the cost, size, weight, and wiring complexity and reduces the mechanical robustness and the reliability of the overall PMSM drive systems. The goal of the research for this dissertation was to develop a rotor position/speed sensorless control system with performance comparable to the sensor-based control systems for PMSMs over their entire operating range.

In this work, different sensorless control methods were developed for different speed regions. In the medium- and high-speed regions, quasi-sliding-mode observer-based position estimators were proposed to obtain rotor position information. Several assistive algorithms, including an online observer parameter adaption scheme, a model reference adaptive system based speed estimator, and an estimated speed-based oscillation mitigation scheme, were proposed to improve the performance of the rotor position estimation and the sensorless PMSM control system. The proposed methods were effective for both salient-pole and nonsalient-pole PMSMs. In the low-speed region, saliency tracking observers are commonly used for rotor position estimation of salient-pole PMSMs. However, for a nonsalient-pole PMSM, due to the symmetric rotor structure, the dependence between rotor position and spatial saliency is weak. This research proposed a novel high frequency square-wave voltage injection-based rotor position estimation method, which is much less dependent on the machine rotor asymmetry and is well suited for nonsalient-pole PMSMs.

The proposed sensorless control offers an effective means to solve the problems incurred in using position sensors in PMSM control systems. Firstly, it provides an alternative to existing sensor-based controls for PMSMs with reduced cost, size, weight, and hardware complexity. Second, it can be used as a supplementary (backup) function in the sensor-based control systems, when the sensor failure occurs. Moreover, the estimated rotor position and speed and other state variables of the PMSMs can be used for condition monitoring of the position sensors and other components in the PMSM drive system.

Advisor: Wei Qiao