Differential magnetic anisotropy - prerequisite for rotor position detection of PM-synchronous machines with signal injection methods

It is well known that rotor position detection at very low speed and at standstill is only possible with signal injection methods, because at vanishing speed the different methods using the induced voltage (back EMF methods) are not suitable. All signal injection methods need as a prerequisite the existence of a magnetic anisotropy of the machine over a wide range of operating conditions. This document presents first the basic theory of electrical machines to derive the needed machine properties which are the prerequisite for rotor position detection at standstill with signal injection methods. Different machine designs with concentrated windings will be analyzed in view of the differential magnetic anisotropy by means of finite element field calculations. Results from prototype measurements will also be presented and compared with the theoretical findings.