Control of Synchronous Motors

Chapter 9

Sensorless Control of Permanent Magnet Synchronous Machines: Deterministic Methods, Convergence and Robustness ¹

9.1. Introduction

The vector control of permanent magnet synchronous machines (PMSM) requires specific information on the rotor position. This information, necessary for the machine control, is usually supplied by a position sensor set on the machine shaft. There are many disadvantages to the use of this mechanical sensor. First, it increases the volume and the global cost of the system. Moreover, it requires an available shaft extension, which is usually undesirable, particularly in the case of small machines. The installation of this sensor requires a setting relative to the stator (an operation tricky to reproduce in series) and decreases the system reliability. The cost of mechanical sensors and the difficulty of placing them encourage researchers to avoid their use and to study mechanical sensorless control [MAT 92], [AFS 94], [BRU 96], [MAT 96], [BOL 99], [BOD 99] and [HAR 00].

The back-EMF is one of the magnitudes able to supply instantaneous information on the mechanical variables. Its determination requires only the knowledge of some electric variables and of an appropriate model of the machine. This is why a large number of studies carried out in the field of sensorless vector control of the PMSM rely on the estimation of the “back-EMF vector”. There are two categories of methods for estimating the “back-EMF vector”:

- methods based on the estimation ...