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Chattering is inevitable in most sliding-mode controllers due to finite and imperfect switching. Most of the discrete-time sliding-mode schemes reported to date fail to alleviate chattering effectively; even under perturbation-free conditions, chattering is still inevitable. This present work proposes a scheme that can guarantee both one-sided behavior and chattering-free performance with uncertainties of the known bounds of the plant. This scheme is applied to the design of a seek-controller for an optical pick-up head to illustrate its feasibility. Both simulation and experimental studies were performed to further validate its effectiveness.

This paper proposes a global sliding mode control (GSMC) scheme that can guarantee a chattering-free performance for systems without external perturbations and ensure a chattering-alleviated performance under the perturbations of known bounds. The GSMC has been a remarkable control technique and is designed to achieve extremely robust performance. This perfectly robust control, however, suffers from the same problem as the conventional sliding mode control, i.e. the chattering problem due to switching control. In this paper, the GSMC scheme employs a smooth function for the switching device to alleviate the chattering phenomenon. Moreover, the proposed scheme uses an auxiliary compensator not only to establish the sliding condition for an ideal system but also to specify directly the dynamic characteristics of the sliding variable. According to Lyapunov's direct method, an explicit condition to ensure a stable attractor is derived. Experimental studies of designing a positioning system with a permanent magnet a.c. servomotor are conducted to illustrate further the feasibility and effectiveness of the proposed scheme.

In this study, a perturbation compensator is introduced in the sliding mode control (SMC) through a function of the prespecified sliding function, which is capable of estimating the lumped uncertainty and external disturbance with a known bandwidth. The approaches are designed to ensure a stable attraction and to attenuate the perturbation, which can be determined through the frequency domain analysis. Furthermore, an upper bound on the perturbation estimating error can be obtained based on the designed parameters, which depend on the bandwidth of the perturbation and the resonant frequency of the proposed estimator. Owing to the fact that the gain margin at zero frequency is infinity, the constant load disturbance can be estimated exactly. Combining the estimator with the sliding mode control method not only drastically reduces the gain of the discontinuous control term as compared with a conventional sliding mode control scheme but also achieves a chattering alleviated performance. In contrast to the SMC, the switching action is then performed in the bandwidth of the proposed compensator. For a disturbance-free system, this scheme not only establishes the sliding condition but also directly specifies the dynamic characteristics of the controlled system during the reaching stage, in which a discontinuous term is not needed. Experimental studies for the design of a turntable spindle servo system are conducted to illustrate its feasibility and effectiveness.

A discrete-time hierarchical sliding-mode control scheme for a dual-stage tracking control system with bounded parameter variation and external disturbance is proposed in this study. This scheme is capable of performing a positioning servo control task that requires driving both coarse tracking and fine tracking stages simultaneously. The desired tracking performances, both the coarse tracking and fine tracking, are ensured. The settling time of the controlled system could be pre-specified by selecting a sliding hyperplane. Furthermore, explicit conditions, involving inequality constraints on the controller parameters, to ensure a one-sided behavior, quasi-sliding mode and chattering-alleviated performance with uncertainty and/or external perturbation of known bounds of the plant are derived. Experimental studies on the design of a track-seeking controller for an optical pick-up head is conducted to further illustrate its feasibility and effectiveness. The experimental results also demonstrate that the proposed scheme provides better performance than a discrete-time sliding mode control method with controller switching method.

Chattering phenomenon is inevitable in most sliding-mode controllers due to finite switching or imperfect switching. Even under perturbation-free condition, chattering is still inevitable as well. This present work proposes a scheme that can guarantee a one-sided behavior performance and chattering-alleviated performance with uncertainty of known bounds of the plant. This scheme is applied to an optical pick-up head positioning system to illustrate its feasibility. Simulation study is performed to validate its effectiveness.

The authors present a novel variable-structure control (VSC) technique for UPS inverters. Unlike other approaches in which all control objects are achieved by a single switching surface function, the proposed inverters employ multiloop control in which the regulation of output voltage as well as inductor current is in terms of its own VSC. In addition, the smooth function is adopted to prevent infinite switching of comparator and alleviate the chattering effect. It follows that the inverters are capable of being current limited and switched with constant frequency. Owing to the robustness of VSC, the output voltages of the inverters have the features of low distortion, fast dynamic regulating speed and insensitivity to load and input voltage variations. A 2 kVA single-phase system is implemented, and both simulated and experimental results are provided to prove the effectiveness of the proposed approach. Applicability to three phase systems, demonstrated by simulated results, is also included.