Contents I. Introduction
Permanent magnet synchronous machines (PMSMs) are widely employed in servo control, automotive, aerospace, and wind power generation systems due to its high power density, high efficiency, and simple structure [1], [2], [3]. For improved system performance, high-performance control strategies rely on sensors to obtain accurate information of rotor position and speed. Thus, position sensor such as the optical encoder or a resolver needs to be installed on the machine shaft. The employment of these extra position detecting devices and associated signal processing equipment for position information, on the other hand, is well known to increase costs. In reality, not only is the cost of the position sensor itself considered, but also the cabling, the appropriate connectors and the interfaces, and all associated expenses have to be considered as well [4]. Besides, the encoder also reduces the system reliability since it is susceptible to harsh environment. Therefore, various sensorless control algorithms for the elimination of speed and position sensors have been proposed.
