Measuring Magnetic Characteristics of Synchronous Machines by Applying Position Estimation Techniques

The torque produced by synchronous machines is a function of stator current and flux linkage. Due to magnetic saturation, the relation between both is nonlinear. In other words, the inductances of a motor are operating 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 paper proposes a method that applies position estimation algorithms from anisotropy-based sensorless control schemes to measure the relation between flux linkage and stator current. The method works for different types of synchronous machines. Measurement results of an interior permanent magnet (PM) and a surface PM motor are presented and compared with results obtained with a conventional electromotive force-based measurement method.