Keqi Mei

Bio: Keqi Mei is an academic researcher from Jiangsu University. The author has contributed to research in topics: Integrator & Control theory. The author has an hindex of 4, co-authored 15 publications receiving 307 citations.

Disturbance Observer Design for Nonlinear Systems Represented by Input–Output Models

Abstract: A new approach to the design of nonlinear disturbance observers (DOBs) for a class of nonlinear systems described by input–output differential equations is presented in this paper. In contrast with established forms of nonlinear DOBs, the most important feature of this new type of DOB is that only measurement of the output variable is required, rather than the state variables. An inverse simulation model is first constructed based on knowledge of the structure and parameters of a conventional model of the system. The disturbance can then be estimated by comparing the output of the inverse model and the input of the original nonlinear system. Mathematical analysis demonstrates the convergence of this new form of nonlinear DOB. The approach has been applied to disturbance estimation for a linear system and a new form of linear DOB has been developed. The differences between the proposed linear DOB and the conventional form of frequency-domain DOB are discussed through a numerical example. Finally, the nonlinear DOB design method is illustrated through an application involving a simulation of a jacketed continuous stirred tank reactor system.

A New Second-Order Sliding Mode and Its Application to Nonlinear Constrained Systems

Abstract: This note considers the second-order sliding-mode (SOSM) control of nonlinear constrained systems. A new state-saturated-like SOSM algorithm has been constructed by using the saturation technique and the backstepping-like method. The finite-time stability of the closed-loop SOSM dynamics has been verified by Lyapunov analysis. The advantage of the proposed SOSM algorithm lies in that it will provide the maximum domain of attraction under the preset state constraints. An example of a pendulum control system has been given to verify the effectiveness of the proposed method.

Second-Order Sliding Mode Controller Design Subject to an Upper-Triangular Structure

Abstract: The second-order sliding mode (SOSM) controller design problem for a class of sliding mode dynamics subject to an upper-triangular structure has been discussed in this paper. The proposed SOSM controller design involves two steps. First, a Lyapunov-based SOSM controller is developed by using the adding a power integrator technique to locally finite-time stabilize the sliding variables. Second, by combining the local SOSM controller with a saturation function, a novel SOSM controller with a saturation level is constructed. The feature of the new SOSM controller lies in that the saturation level can be tuned not only to guarantee the global convergence but also to improve the dynamic performance. Lyapunov analysis has been utilized to test the finite-time stability of the closed-loop sliding mode dynamics. The proposed method is eventually demonstrated by simulation results.

Fixed-time SOSM controller design with output constraint

Abstract: In this paper, a novel fixed-time second-order sliding mode (SOSM) controller has been developed for a class of nonlinear systems with output constraints. Based on the output constraint condition, a new barrier Lyapunov function, which can be used to deal with the output constraint, is first constructed. Then, with the help of adding a power integrator technique, the SOSM algorithm can be constructed step by step. The feature of the proposed SOSM algorithm lies in that it will not only fixed-time stabilize the sliding variable to the origin, but also keep the output variable staying inside the constraint set. This also implies that the setting time of sliding variables will be independent of their initial conditions. Finally, the feasibility and effectiveness of proposed SOSM control method are verified by a numerical example and a practical pendulum system.

Adaptive Fuzzy SOSM Controller Design With Output Constraints

Abstract: The output constraints are widespread in physical systems. Violation of output constraints may result in system damage and performance degradation. This paper investigates the design issue of adaptive fuzzy second-order sliding mode (SOSM) controller, which aims to handle a class of nonlinear systems with output constraints. The unknown bounds of uncertainties are approached dynamically by fuzzy logic systems. Through designing a new barrier Lyapunov function, the output constraint problem has been well solved. Then, by integrating adding a power integrator (API) technology and adaptive fuzzy control, a novel adaptive fuzzy SOSM controller is proposed. It is proved that the proposed method makes the output variable not violate the specified constraint region. At the same time, it can be shown based upon the Lyapunov approach that the finite-time stability of the resulting closed-loop system under output constraint is ensured. Finally, a numerical example and a practical pendulum system are presented to demonstrate the validity of the proposed SOSM control strategy.

Disturbance Observer Design for Nonlinear Systems Represented by Input–Output Models

Abstract: A new approach to the design of nonlinear disturbance observers (DOBs) for a class of nonlinear systems described by input–output differential equations is presented in this paper. In contrast with established forms of nonlinear DOBs, the most important feature of this new type of DOB is that only measurement of the output variable is required, rather than the state variables. An inverse simulation model is first constructed based on knowledge of the structure and parameters of a conventional model of the system. The disturbance can then be estimated by comparing the output of the inverse model and the input of the original nonlinear system. Mathematical analysis demonstrates the convergence of this new form of nonlinear DOB. The approach has been applied to disturbance estimation for a linear system and a new form of linear DOB has been developed. The differences between the proposed linear DOB and the conventional form of frequency-domain DOB are discussed through a numerical example. Finally, the nonlinear DOB design method is illustrated through an application involving a simulation of a jacketed continuous stirred tank reactor system.

Reduced Adaptive Fuzzy Tracking Control for High-Order Stochastic Nonstrict Feedback Nonlinear System With Full-State Constraints

Abstract: This paper focuses on the design of a reduced adaptive fuzzy tracking controller for a class of high-order stochastic nonstrict feedback nonlinear systems with full-state constraints. In the proposed approach, reduced fuzzy systems are used to approximate uncertain functions which involve all state variables and a high-order tan-type barrier Lyapunov function (BLF) is considered to deal with full-state constraints of the controlled system. With this BLF and a combination of the reduced fuzzy control and adding a power integrator, a novel control scheme is constructed to ensure that tracking error is within a very small range of the origin almost surely, meanwhile, the constraints on the system states are not breached almost surely during the operation. Two examples are proposed to show the effectiveness of the design scheme.

Improved Non-Singular Fast Terminal Sliding Mode Control With Disturbance Observer for PMSM Drives

Abstract: For the purpose of shortening response time and improved anti-disturbance performance of the permanent magnet synchronous motor (PMSM) drives, a compound control method using improved non-singular fast terminal sliding mode controller (NFTSMC) and disturbance observer compensation techniques are developed. First, in order to overcome the contradiction between fast response and heavy chattering of the conventional NFTSMC, a new sliding mode reaching law (NSMRL) is proposed for the improved NFTSMC. The NSMRL, which allows chattering reduction on control output while maintaining high tracking performance of the controller, can dynamically adapt to the variations of the controlled system. Second, to further improve the anti-disturbance performance of the PMSM control system, the sliding mode disturbance observer (SMDO) is introduced to estimate the load disturbance and add to the output of the improved NFTSMC for a feed-forward compensation item. Finally, both the simulation and experimental results applied to PMSM drives show that the proposed control method has better suppression of chattering effect, fast dynamic response, and disturbance rejection ability.

Network-based passive estimation for switched complex dynamical networks under persistent dwell-time with limited signals

Abstract: In this paper, the state estimation issue for a set of switched complex dynamic networks affected by quantization is studied, in which the switching process is assumed to follow persistent dwell-time switching regulation. Thereinto, the switching regulation aforementioned describes the switchings among different parameters on complex dynamic networks. Meanwhile, for the network-based model, in the communication channels from the sensor to the estimator, quantization is inevitable to be taken into consideration. To track partially inaccessible information in the target system, a state estimator is thoroughly reconstructed. Intensive attention is that a set of sufficient conditions can be derived by using some simple matrix transformation methods, linear matrix inequality and Lyapunov stability theory, to further assure the error dynamic obtained is globally uniformly exponentially stable and meets passive property. The serviceability of the state estimator gains solved is finally verified and the effectiveness of the proposed design approach is further illustrated.