In this article, a novel adaptive super-twisting nonlinear Fractional-order PID sliding mode control (ASTNLFOPIDSMC) strategy using extended state observer (ESO) for the speed operation of permanent magnet synchronous motor (PMSM) is proposed. Firstly, this paper proposes a novel nonlinear Fractional-order PID (NLFOPID) sliding surface with nonlinear proportion term, nonlinear integral term and nonlinear differential term. Secondly, the novel NLFOPID switching manifold and an adaptive supertwisting reaching law (ASTRL) are applied to obtain excellent control performance in the sliding mode phase and the reaching phase, respectively. The novel ASTNLFOPIDSMC strategy is constructed by the ASTRL and the NLFOPID sliding surface. Due to the utilization of NLFOPID switching manifold, the characteristics of fast convergence, good robustness and small steady state error can be ensured in the sliding mode phase. Due to the utilization of ASTRL, the chattering phenomenon can be weakened, and the characteristics of high accuracy and strong robustness can be obtained in the reaching phase. Further, an ESO is designed to achieve dynamic feedback compensation for external disturbance. Furthermore, Lyapunov stability theorem and Fractional calculus are used to prove the stability of the system. Finally, comparison results under different controllers demonstrate that the proposed control strategy not only achieves good stability and dynamic properties, but also is robust to external disturbance. INDEX TERMS Adaptive super-twisting nonlinear Fractional-order PID sliding mode control (ASTNL-FOPIDSMC) strategy, extended state observer (ESO), permanent magnet synchronous motor (PMSM), nonlinear Fractional-order PID (NLFOPID) sliding surface, adaptive super-twisting reaching law (ASTRL).

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A novel sliding mode controller (SMC) with nonlinear fractional order PID sliding surface based on a novel extended state observer for the speed operation of a surface-mounted permanent magnet synchronous motor (SPMSM) is proposed in this paper. First, a new smooth and derivable nonlinear function with improved continuity and derivative is designed to replace the traditional nonderivable nonlinear function of the nonlinear state error feedback control law. Then, a nonlinear fractional order PID sliding mode controller is proposed on the basis of the fractional order PID sliding surface with the combination of the novel nonlinear state error feedback control law to improve dynamic performance, static performance, and robustness of the system. Furthermore, a novel extended state observer is designed based on the new nonlinear function to achieve dynamic feedback compensation for external disturbances. Stability of the system is proved based on the Lyapunov stability theorem. The corresponding comparative simulation results demonstrate that the proposed composite control algorithm displays good stability, dynamic properties, and strong robustness against external disturbances.

In this research, based on the ultra-local model, a novel compound model-free control strategy with an intelligent Proportional-Integral and super-twisting Sliding Mode Control (MFiPISTSMC) strategy for permanent magnet synchronous motor (PMSM) drives is proposed. Firstly, an intelligent Proportional-Integral (iPI) control strategy is designed for motor speed regulation. Secondly, a super-twisting Sliding Mode Control (STSMC) strategy is constructed based on the ultra-local model of PMSM. At the same time, the unknown term of the ultra-local model of PMSM is estimated by a Linear Extended State Observer (LESO). The stability of the compound MFiPISTSMC strategy is proved by the Lyapunov stability theorem. As a result of the compound MFiPISTSMC strategy integrating the STSMC strategy, the iPI control strategy and the LESO is proposed to have excellent performance. Finally, the static characteristic, dynamic characteristic and robustness of the novel compound MFiPISTSMC strategy are verified by simulation and experimental results.

This paper proposes a novel model-free super-twisting nonlinear sliding mode control (MFSTNLSMC) strategy with an improved smoothing extended state observer (SESO) for permanent magnet synchronous motor (PMSM) drives. First of all, the improved SESO is introduced to estimate the unknown term of the PMSM ultra-local model. Secondly, a novel nonlinear sliding mode surface (NLSMS) is designed, which can effectively overcome the disadvantages of simple and rough signal processing of the conventional linear sliding mode surface. At the same time, a super-twisting (ST) structure is chosen to suppress the chattering phenomenon and improve system robustness. Then, the Lyapunov stability theorem is used to prove the stability of the proposed control algorithm. Finally, both comparative simulations and experimental demonstrations verify the excellent speed tracking performance and robustness of the proposed control strategy.

How to improve head-disk interface (HDI) characteristics in the mechanical design of hard-disk drives (HDDs) has become increasingly important due to the ever-growing demand for storage density and speed of access. In this paper, a means of active actuation and control of the suspension structure in HDDs is investigated and it is used to reduce head-disk friction/wear and to suppress induced vibrations. The analytical model for a cantilever-beam-like structure with the bonded piezo films is presented. A constant-gain velocity feedback control is proposed and its effectiveness in suppressing induced vibrations is demonstrated both theoretically and experimentally.

In the 21 st century, the importance of helping students become more autonomous in their learning has become one of its most prominent themes. Autonomy is usually defined as the capability to take charge of, or responsible for, one's own learning. Nowadays, autonomy is widely accepted as a desirable goal in education. With promoting learner autonomy as the ultimate goal of education comes the question of how to foster learner autonomy. In this essay, we are arguing for the provision of circumstances and contexts for language learners through developing process syllabuses in the language classroom to help them make decisions for their own learning through negotiations. This practice of negotiated syllabus emphasizes the value of collaborative learning, learner-centredness, learner autonomy and shared decision making. We practiced producing process syllabus in the Advanced Speaking and Listening Course between 2006 and 2008 and we found out that through negotiations of purposes, contents, ways of working and evaluation, students are going through the various stages of producing languages and by shifting the power into students' hands, they become highly motivated and whole-heartedly involved and take on greater responsibility for their own learning.

An active magnetic bearing (AMB) is a kind of high-performance bearing that uses controllable electromagnetic force to levitate the rotor. Its control performance directly affects the operation characteristics of high-speed motors and other electromechanical products. The magnetic bearing control model is nonlinear and difficult to control. Sliding mode control algorithm can be used in the magnetic bearing control system, but the traditional sliding mode control has the problem of high-frequency chattering, which affects the operation stability of magnetic bearings. Based on the second-order sliding mode control algorithm, a new second-order sliding mode controller for active magnetic bearing control was designed, and the stability of the designed sliding mode control law was proven by Lyapunov criterion. On the basis of the established active magnetic bearing control model, the numerical analysis of the designed controller was carried out, and the control effect was compared with that obtained by the exponential reaching law for the sliding mode control algorithm. The experimental results show that the designed sliding mode controller has better dynamic performance and stability than the exponential reaching law for the sliding mode controller.