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To improve the accuracy of permanent magnet (PM) rotor position estimation for a hybrid stepper motor (HSM), the authors propose a sensorless control design based on the back electromagnetic force (back-EMF) caused by magnetic induction and harmonic rejection via an orthogonal third-order phase-locked loop (PLL3rd) and an integral harmonic filter (IHF). The accuracy of estimation is analysed considering PM rotor position estimation errors. The harmonics of the back-EMF signal are eliminated by the IHF before entering the PLL3rd, which synchronises and decreases position estimation error. This technique is a simple, reliable, and effective method for implementing sensorless control of an HSM. An industrial test-bench was used to implement the proposed scheme. The experimental results are presented to validate the effectiveness of the proposed estimation method. [ABSTRACT FROM AUTHOR]

Hybrid stepper motors, which convert the input pulse train into rotating angle increments by using an open-loop control strategy, are widely used in industrial applications. The bearing is a key and vulnerable component in stepper motors, and the bearing faults affect the positioning accuracy and output torque of motors. Order analysis is an effective method in bearing fault diagnosis under varying speed conditions. The rotating angle curve is necessary for order analysis, but angle or speed sensors are not installed on hybrid stepper motors. In this article, a method of estimating the rotating angle from motor current is proposed and applied to bearing fault diagnosis. First, a variational nonlinear chirp mode decomposition method is introduced to decompose the current signal and extract a dominant mode that has a strong correlation with motor rotation. Second, the rotating angle is calculated, and the synchronous vibration signal is resampled using the rotating angle curve. Finally, the bearing fault type is identified from the envelope order spectrum of the resampled signal. The proposed method can accurately diagnose bearing faults and has potential applications in condition monitoring of stepper motors. [ABSTRACT FROM AUTHOR]

Sensorless control of permanent magnet synchronous machines (PMSM) down to zero speed using high-frequency (HF) signal injection is an established method. Stable operation during transient states still presents a challenge for this method, especially for motors with very small anisotropies. This paper introduces a new method for stabilizing the sensorless control scheme. It is shown that a misalignment between the estimated dq coordinate system and the actual rotor position causes a variation of the high-frequency current amplitude. Calculated values based on theoretical observation are compared to actual measurements of a hybrid stepper motor used as a PMSM. Several issues that can be used to determine if a motor is suitable for this approach are addressed. Finally, the effectiveness of the new control scheme is validated by implementation in the existing sensorless control of a hybrid stepper motor. [ABSTRACT FROM AUTHOR]