Enhanced sensorless controllability of PMSM - A novell rotor asymmetry approach

Methods for estimating the rotor position of permanent magnet synchronous machines (PMSM) from standstill to medium speed, are generally based on magnetic anisotropies and as a consequence on differences between direct and quadrature stator inductances (L_sd and L_sq). As one possibility, a high frequency (HF) rotating carrier signal injection can be used for a kind of modulating the rotor position and finally applied for sensorless control. The performance of such a method depends very much on the chosen motor topology. Methods which potentially advance the effects of anisotropy are of general interest. This paper introduces a novel approach for enhancing sensorless controllability of PMSM, especially if HF rotating carrier signals are used. The basic idea is to design and implement a rotor asymmetry, which causes, beside the material based rotor anisotropy, an additional effect on the difference between L_sd and L_sq. The substantial progress of this novel approach is that the effect can be controlled by the HF signal parameters like frequency and amplitude. First, the paper lines out the general field of sensorless control of PMSM, followed by some theoretical considerations of the mentioned effect. Second, theory gets underpinned by simulation results. Finally, experiments and measurement results indicate that in case of the used motor topology, the effect under investigation is not significantly distinctive. Because of that lack, at the very end of this paper ideas and an outlook for future research work are presented.