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The sliding-mode observer (SMO)-based voltage model (VM) design is an effective way to improve the robustness of speed estimation in sensorless induction motor (IM) drives. However, this article reveals that the existing SMO-based VM is unable to remove the dc offset present in the rotor flux derivative, resulting in the integral drift problem of rotor flux estimation. To address this problem, this article proposes a SMO-based closed-loop VM observer based on the orthogonality between the rotor flux and its derivative. First, by introducing the orthogonality into the design of observer structure, the rotor flux estimation can be incorporated into the stator current observer. Second, by ensuring the stability of current observer, the SMO law can compensate the deviation between the estimated rotor flux and the ideal orthogonality. Finally, the SMO law will act as the feedback term to remove the dc offset in the rotor flux derivative and stabilize the pure integral for rotor flux estimation. The contrast and verification experimental results from a 2.2-kW IM test bench confirm the accuracy and robustness improvement of rotor flux and speed estimation.

There are multisource disturbances in permanent magnet synchronous motor (PMSM) drives, which can lead to speed fluctuations, deteriorating the speed control performance. The existing terminal sliding mode controller (TSMC) methods cannot achieve the desired control performance when they are applied as the speed controller. This is because these methods do not overcome the inherent problems of the traditional TSMC, such as the chattering phenomenon and differential calculation. To solve this problem, this article proposes an integrated observer-based TSMC for the speed regulation of PMSM drives. First, a TSMC is proposed. Then, an error-based extended state observer with generalized integrators is proposed and it is introduced to the proposed TSMC. In the proposed scheme, the proposed observer is employed to estimate the multisource disturbances, which are adapted to the TSMC to attenuate the chattering level. In addition, the proposed observer contains the speed error differential signal, which can be employed for the calculation of the TSMC. Thus, the proposed scheme can solve the inherent problems of traditional TSMC. Compared with the existing TSMC methods, the proposed scheme can achieve the desired control performance even in the presence of multisource disturbances when it is employed as the speed controller. Finally, the effectiveness of the proposed scheme is validated on a 2.2-kW PMSM platform.

For the high-end industrial application of induction motors (IMs), the speed controller is expected to possess strong torque rejection capability to suppress the speed fluctuation. To accomplish this goal, this article proposes a second-order terminal sliding-mode (SO-TSM) speed controller with nonlinear control gain. First, a SO-TSM manifold is designed to introduce the convergence trajectory without speed overshoot. Second, an integral term control law is constructed to compensate external disturbance with the antiwindup mechanism. The analysis of convergence trajectory shows that the torque rejection capability of the studied method is represented by the gain value of the integral term. Thus, the studied nonlinear control gain can improve the torque rejection capability and suppress the chattering simultaneously. Finally, the experimental results from a 3.7 kW IM test bench reveal the strong torque rejection capability of the studied method.

For speed-sensorless induction motor (IM) drives, the high-order sliding-mode observer (SMO) can improve the robustness of speed estimation. However, it is difficult for the existing high-order SMOs to ensure finite-time convergence, resulting in performance degradation or even instability in the wide-speed range. To address this problem, a high-order SMO with adaptive gain is proposed based on the motor operation speed. First, a high-order sliding-mode surface is designed to achieve finite-time convergence of the rotor flux estimation in the reference model. Then, an adaptive gain is proposed to guarantee the stability of the high-order SMO in the wide-speed range. Second, an improved discretization method is introduced to ensure the stability and reduce the discretization error in the adaptive model. On this basis, the rotor speed is further obtained by the model reference adaptive system. Compared with the existing SMOs, the investigated method can achieve finite-time convergence and guarantee the estimation stability in the wide-speed range, including field-weakening range. Finally, the experimental results from a 3.7 kW IM test bench reveal the effectiveness of the investigated strategy.

By ensuring the finite-time convergence to equilibrium point under disturbance, the high-order terminal sliding-mode (HO-TSM) current controller can improve the system robustness for induction motor (IM) drives. However, the existing HO-TSM still suffers from the drawback that it cannot obtain rapid convergence and effective chattering suppression simultaneously. To address this problem, a fast HO-TSM current controller is studied with the modifications from three aspects. First, a fast HO-TSM surface is designed to improve the convergence speed when the system state is on the designed surface. Second, the control law is modified with a linear integral term to enhance the capability of disturbance compensation. Third, a nonlinear gain is introduced to adjust the gain value, leading to satisfactory chattering suppression during steady state. Compared with conventional HO-TSM, the studied method can achieve strong robustness to disturbance, rapid convergence, and improved chattering suppression capability at the same time. Finally, the superiority of studied method is verified by the experimental results from a 3.7 kW IM test bench.

By combining the high robustness of sliding-mode observer (SMO) with the adaptability of model reference adaptive system (MRAS), the sliding-mode-based MRAS can improve the speed estimation performance of speed-sensorless induction motor (IM) drives. However, the analysis of this article shows that there exists a mismatch problem between the fixed-value of SMO gains and the variable stability boundary, which changes with IM operation speed, resulting in speed estimation performance degradation or even instability in high-speed range. To cope with this problem, a discrete SMO is proposed to expand the effective operation range of sliding-mode-based MRAS. First, a discrete terminal SMO with modified observer structure is designed for rotor flux estimation. Then, a variable gain is designed to ensure the SMO stability in high-speed range, and avoid the chattering caused by gain value overestimation. Compared with existing sliding-mode-based MRAS, the studied method can improve the stability and accuracy of speed estimation in high-speed range. Finally, the experimental results from a 3.7 kW IM test bench can confirm the validness of studied speed estimation scheme.