Abstract
This paper presents an original adaptive sliding mode control strategy for a class of nonlinear systems on the basis of uncertainty and disturbance estimator. The nonlinear systems can be with parametric uncertainties as well as unmatched uncertainties and external disturbances. The novel adaptive sliding mode control has several advantages over traditional sliding mode control method. Firstly, discontinuous sign function does not exist in the proposed adaptive sliding mode controller, and it is not replaced by saturation function or similar approximation functions as well. Therefore, chattering is avoided in essence, and the chattering avoidance is not at the cost of reducing the robustness of the closed-loop systems. Secondly, the uncertainties do not need to satisfy matching condition and the bounds of uncertainties are not required to be unknown. Thirdly, it is proved that the closed-loop systems have robustness to parameter uncertainties as well as unmatched model uncertainties and external disturbances. The robust stability is analyzed from a second-order linear time invariant system to a nonlinear system gradually. Simulation on a pendulum system with motor dynamics verifies the effectiveness of the proposed method.
Highlights
Sliding mode control (SMC) is one of distinguished control methods because of its strong external disturbance rejection and parameter variations insensibility performance when matching condition holds
This paper presents an original adaptive sliding mode control strategy for a class of nonlinear systems on the basis of uncertainty and disturbance estimator
A novel uncertainty and disturbance estimatorbased adaptive sliding mode control (UDE-based ASMC) method is presented for nonlinear systems, which are with parameter uncertainties as well as unmatched model uncertainties and external disturbances
Summary
Sliding mode control (SMC) is one of distinguished control methods because of its strong external disturbance rejection and parameter variations insensibility performance when matching condition holds. One of the main obstacles for application of SMC is chattering, and when discontinuous term exists in control signal, chattering cannot avoid essentially. Reference [2] presented a chatteringfree second-order sliding mode control method for a class of multi-input systems. While [3] analyzed the chattering phenomenon in systems with second-order sliding modes. Since the amplitude of chattering is proportional to the discontinuity magnitude in control signal, adaptivity principles are employed to reduce the effect of chattering. Reference [8] discussed sliding order and proposed “super-twist” controller, [9] proposed an adaptive sliding mode control for discrete-time systems. Reference [10] developed and discussed different SMC algorithms with adaptive process to tune control gain. In [11], the control gain is of varying magnitude according to an adaptation process, but the adaptation process is terminated once sliding mode starts
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