On the Rotor Position Self-Sensing Capability of Reluctance and IPM Synchronous Motors

Iron saturation affects the low-speed and standstill rotor position estimation of synchronous motors based on high frequency voltage injection, leading to an estimation error. In the case of a heavily saturated machine, the estimation algorithm could even fail, due to the absence of convergence points, making the sensorless drive impractical. This article examines in depth the mentioned problem of convergence in salient rotor machines; a synchronous reluctance motor is assumed as case study since this kind of machine is considerably affected by iron saturation. At first, the article models and describes in detail the high frequency voltage injection estimation mechanism. Then it analyzes the convergence conditions and investigates the dependence of the estimation convergence range on the amplitude and phase of the reference current vector of the drive. Moreover, it proposes different methods to enhance the estimation convergence range, improving the accuracy as well. A comparison between the different approaches is given as well as hints for their design. At last, the impact of airgap space harmonics is pointed out. The results are validated by simulations and experimental tests.