Measuring magnetic properties of synchronous machines by applying angle estimation techniques known from sensorless control

Abstract

The torque produced by synchronous machines is a function of stator current and flux linkage. Due to magnetic saturation, the relation between both is non-linear. With other words, the inductances of a motor are set point dependent. In many applications, however, magnetic saturation is neglected in order to simplify the model of the motor. If, on the other hand, a precise model is needed (e.g. for efficiency improvements), it is useful to measure the flux linkage depending on the current (or vice versa). This work proposes a method that applies angle estimation algorithms from anisotropy-based sensorless control schemes to measure the relation between flux linkage and stator current. The method is independent from the mechanical speed of the drive and works for different types of synchronous machines. Measurement results are presented and compared to results obtained with a conventional emf-based measuring method.