Limit Cycle Analyses of Extended EMF-Based Position-Sensorless in IPMSM Drives

This article reveals a limit cycle issue in the widely used position estimation method of interior permanent magnet synchronous motors (IPMSMs) based on extended back electromotive force (EMF). The limit cycle can result in self-oscillations in the estimated rotor position and greatly increase the estimation errors. In this article, a nonlinear model is proposed to analyze the arctangent nonlinearity involved in the EMF method, and a describing function approach is employed to derive the critical criteria for limit cycle issue. The result shows that a limit cycle will be excited when the parameters of the phase-locked loop exceed the critical value. The parameter boundary is determined by the operating conditions and motor parameters, which facilitates the tuning of sensorless control. Theoretical analyses are verified on the IPMSM setup, of which experimental results confirm the correctness of the proposed analysis in predicting the autonomous oscillation in extended EMF-based position estimation.