A Frequency Domain Interpretation of Signal Injection Methods for Salient PMSMs

Several heuristic procedures to estimate the rotor position of interior permanent magnet synchronous motors via signal injection have been reported in the applications literature, and are widely used in practice. These methods, based on the use linear time invariant high-pass/low-pass filters, are instrumental for sensorless controllers. To the best of our knowledge, no theoretical analysis has been carried out for them. The objectives of this note, are (i) to invoke some recent work on the application of averaging techniques for injection-based observer design to develop a theoretical framework to analyze the sensorless methods, and (ii) to propose a new method that, on one hand, ensures an improved accuracy and, on the other hand, can be related with the current filtering technique. An additional advantage of the new method is that it relies on the use of linear operators, implementable with simple computations. The effectiveness of the proposed scheme is assessed by experiments.