A Robust and Practical Approach to Estimate the Number of Shorted Turns in PMSM With ITSC Faults

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Abstract
This paper puts forward a novel method to estimate the fault severity index and consequently the number of shorted turns in permanent magnet motors (PMSM) with inter turn short circuit fault (ITSC). In this method, the machine is excited with DC current at stand still conditions to obtain the winding resistance seen by the d-axis of the machine. The estimated d-axis resistance contains useful information pertaining to the fault severity index, and is used to extract the fault severity index and the number of shorted turns in the faulty motor. The proposed method enables the estimation of fault severity index without complex machine modeling and extensive experiments with different machine prototypes, or Finite Element Analysis (FEA) models to analyze the relationship between machine currents and short circuit current. To enhance the accuracy of the estimation algorithm, this paper addresses practical issues associated with inverter non-linearity effects such as distortion voltage due to dead time effects and voltage drops across the switching devices, and proposes method to estimate the fault severity index that is immune to the aforementioned issues. Determining the fault index is critical in order to design appropriate mitigation techniques, as well as defining a safe operating area for the machine to avoid further damage to the winding. To verify the efficacy of this algorithm, experiments are conducted on a three phase PMSMs with artificial taps that imitate the behavior of inter turn short circuit fault, and results which demonstrates the practicability of this algorithm are presented.
Funding Information
  • Nidec Inc.

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