Of course, this effect is real, and it can be seen in Fig. 7. The deviation of the detected angle, however, is rather small – much smaller than to be expected according to [22]. The reason for that is the design of the rotor of a synchronous machine with permanent magnets. Fig. 10 shows some typi- cal examples. The holes in the rotor are located where there is no iron needed for the main flux, and these are mainly provided for reducing the inertia. As a result the flux pro- duced by the “armature reaction” has to overcome a high magnetic reluctance – as a result the impact of the “armature reaction” on the main flux distribution is much lower than with a full iron rotor. Consequently servo motor designs are suited very well for encoderless control with HF injection methods.