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A speed control of sensorless induction motor (IM) drives at zero and very low frequencies is designed in this paper. A new adaptive sliding mode observer (SMO) to estimate the stator current, rotor flux, and rotor speed is proposed. To improve the robustness and accuracy of an adaptive SMO during very low frequency operation, the sliding mode flux observer uses independent gains of the correction terms. The gains of current and rotor flux SMOs are designed using Lyapunov stability theory to guarantee the stability and fast convergence of the estimated variables. A Lyapunov function candidate utilizing the error of rotor fluxes and speed estimation error is synthesized for speed estimation. Detailed simulations and experiments are given showing the operation of the sensorless speed control at very low frequency. The results prove the accuracy and robustness of the proposed adaptive SMO. Also, comparison results with the state-of-the-art methods prove that the proposed method shows excellent transient and steady-state speed estimation, particularly at very low and zero frequency operations. [ABSTRACT FROM PUBLISHER]

This paper proposes a new approach for separation of saliency signals of the induction machine at very low speed and heavy loads. The change of current responses due to the transient voltage pulse excitation is employed to obtain the inherent impedance saliency information. The proposed separation approach uses the discrete wavelet transform (DWT) in combination with Taylor's expansion and least square error (LSE) methods. The DWT removes the higher and lower harmonic orders to extract the operating frequency band based on the reference speed. Then, Taylor's expansion modeling processed by LSE algorithm is applied to extract the slotting saliency signal from the nearby frequency of the inter-modulation signal. The extracted slotting saliency signal is employed to estimate the rotor/flux position using the phase locked loop observer and current model. Experimental results are provided to prove the effectiveness of the proposed new separation approach at very low speed including zero electrical speed operations. It is found that the proposed new approach is accurate at very low speed and heavy load operations with less noise compared to previous methods. [ABSTRACT FROM AUTHOR]

A novel separation procedure applied to overlap condition of saliencies in induction machine is presented. The machine's current reaction to voltage step excitation is used to obtain saliency signals. The proposed procedure is based on a digital signal processing implementation of the discrete sine and cosine transforms for extracting the slotting saliency signal at close and equal frequencies of the slotting and saturation saliencies under heavy load operation. The proposed algorithms are processed based on an online adaptive threshold. Using the proposed separation algorithm guarantees precise estimation of rotor/flux angle and efficient sensorless control of the induction machine. A sensorless induction motor drive is implemented in the laboratory. Extensive experimental results are presented. A performance comparison between the proposed algorithm and previous works is provided. The robustness and effectiveness of the applied signal processing algorithms for sensorless torque control are verified at low speed and heavy load. [ABSTRACT FROM PUBLISHER]