Junkang Ni

Fast Fixed-time Nonsingular Terminal Sliding Mode Control and its Application to Chaos Suppression in Power System

This brief presents a novel control scheme to achieve fast fixed-time system stabilization. Based on fixed-time stability theory, a novel fixed-time stable system is presented. Using the proposed fixed-time stable system, a fast fixed-time nonsingular terminal sliding mode control method is derived. Our control scheme achieves system stabilization within bounded time independent of the initial condition and has an advantage in convergence rate over the existing result of the fixed-time stable control method. The proposed control strategy is applied to suppress chaotic oscillation in power systems, and its effectiveness as well as superiority is verified through numerical simulation. The proposed control strategy can be applied to address the control and synchronization problem for other complex systems.

Fixed-Time Leader-Following Consensus for Second-Order Multiagent Systems With Input Delay

This paper studies fixed-time leader-following lag consensus problem of second-order multiagent systems with input delay. Using fixed-time distributed observer, we obtain the leaders states for each followers. An extension of the Artsteins reducing transformation is employed to transform the delayed error system into a second-order system without time delay and a novel nonsingular terminal sliding mode protocol is proposed to achieve fixed-time consensus. The presented sliding mode controller can avoid singularity, eliminate chattering, and achieve exact convergence. It is mathematically proved that the presented protocol can achieve exact fixed-time leader-following lag consensus. Moreover, the upper bound of convergence time only depends on observer parameters, controller parameters, network parameters, and delay time, which makes it possible to determine the convergence time offline regardless of initial condition. The presented protocol is applied to coordinated lag tracking control of single-link robotic manipulators and the results validate the effectiveness of the proposed fixed-time protocol.

Chaos suppression for a four-dimensional fundamental power system model using adaptive feedback control

In this paper, the problem of chaos suppression for a four-dimensional fundamental power system (FDFPS) model is considered via the design of a novel adaptive feedback controller. The period doubling bifurcation route to chaos and some dynamical behaviors of the power system are investigated in detail. Based on stability analysis using an energy-type Lyapunov function, a single adaptive feedback controller is derived to suppress chaotic oscillation in four-dimensional fundamental power systems. The proposed controller simplifies the design of power system stabilizer and provides an easy way to implement in practical power system control. In addition, effectiveness of damping out chaotic oscillation and robustness against parameter uncertainty and external disturbance also make the proposed control scheme applicable for industrial application. Simulation results illustrate the effectiveness, the robustness and the superiority of proposed control method.

Chattering-Free Time Scale Separation Sliding Mode Control Design with Application to Power System Chaos Suppression

This paper presents a novel chattering-free sliding mode control method for a class of disturbed nonlinear systems, which achieves fast and exact disturbance estimation, eliminates chattering, and recovers the performance of nominal system and nominal control input. The proposed approach combines time scale separation design and sliding mode control. Different from the existing disturbance estimation based sliding mode control methods, the proposed scheme achieves fast and exact disturbance estimation through time scale separation and eliminates discontinuous switching term, thereby achieving good chattering alleviation effect and providing good transient response. The proposed control method is applied to suppress chaos in power system and simulation results confirm the effectiveness and robustness of proposed control scheme and highlight the advantages of the proposed control scheme over the existing disturbance estimation based sliding mode control methods in terms of chattering alleviation effect and transient response.

Fixed-Time Disturbance Observer Design for Brunovsky Systems

This brief presents a fixed-time disturbance observer for Brunovsky systems. The proposed disturbance observer is composed of a uniform convergent part and a finite time convergent part. The uniform convergent part first drives the estimation error trajectories into a compact set containing the origin and then the finite time convergent part achieves exact disturbance estimation. The proposed disturbance observer can achieve exact disturbance estimation within finite time upper bounded by a constant independent of initial estimation error. In addition, the upper bound of the estimation time can be calculated theoretically. Numerical simulations are provided to demonstrate the effectiveness of the proposed disturbance observer and verify the declared fixed-time property.

Secondary voltage control for microgrids based on fixed-time distributed cooperative control of multi-agent systems

In this paper, fixed-time distributed cooperative control of multi-agent systems is presented for secondary voltage control of microgrids. Fixed-time observer is constructed to estimate the synchronization error and fast fixed-time controller is designed to achieve fixed-time terminal voltage synchronization of each distributed generator in microgrids. The presented control scheme is fully distributed and requires sparse communication links. Therefore, it is more reliable and costs less than centralized control. Furthermore, the presented control scheme can guarantee fixed-time convergence of the synchronization error, which can reduce the loss caused by voltage instability and guarantee excellent power supply quality after restoration. Simulation results validate the effectiveness of the proposed control scheme.