Contents I. Introduction
The mechanical encoder that is in general mandatory for operating electrical machines includes some disadvantages such as the volume and the cost of the machine or the influence of the environment on it. If some requirements are fulfilled, this mechanical part of the machine can be obsolete when using self-sensing control. At higher speeds, techniques based on the back-EMF of the machine are applicable by only evaluating a certain voltage signal of the machine during operation. At declining speeds, however, the signal-to-noise ratio gets worse and the position estimation based on the back-EMF is no longer possible [1]. Hence, an additional test signal needs to be injected. For still being able to estimate the correct rotor position of the machine it requires an electromagnetic saliency, which needs to be present at every rotor position and operating point. The first one is e.g investigated in [2], the latter one in [3]. A general overview of typically used techniques for encoderless control in the present research is carried out in [4]. Cross-coupling effects between the high frequency (HF-) inductances and resistances are the crucial point of these concepts using test signal injection. When the saturation of the machine increases, these effects rise as well [5] and the electromagnetic saliency strongly decreases [2], [6]. For a vanishing saliency, the worst-case scenario is a total loss of the position information.
