Showing papers by "Hassan K. Khalil published in 2021"
TL;DR: It is shown that the agents achieve practical synchronization and the synchronization error can be made arbitrarily small by tuning the high-gain observer parameter.
Abstract: In this article, we consider the synchronization problem in a network of nonlinear multiagent systems having the same relative degree $r$ . The agents do not have access to their state or output and only have relative output information from their neighbors. The controller structure is decentralized in nature and, therefore, depends only on the relative information available to it. The agent dynamics are transformed into relative dynamics by a change of coordinates where the agent dynamics are coupled. Extended high-gain observers are used to estimate the nonlinear coupling at each agent and then cancel them using feedback control. Therefore, the problem changes to a stabilization problem of $N$ nonlinear systems in the relative coordinates. It is shown that the agents achieve practical synchronization and the synchronization error can be made arbitrarily small by tuning the high-gain observer parameter. Finally, simulations are done with a network of power systems to show the efficacy of the proposed controller.
15 citations
TL;DR: Experimental results confirm the performance and robustness of the proposed controller and compare it to the cascaded proportional integral (PI) speed controller.
Abstract: Control of the speed as well as shaping the speed transient response of a surface-mounted permanent magnet synchronous motor (PMSM) is achieved using the method of feedback linearization and extended high-gain observer. To recover the performance of feedback linearization, an extended high-gain observer is utilized to estimate both the speed of the motor and the disturbance present in the system. The observer is designed based on a reduced model of the PMSM, which is realized through the application of singular perturbation theory. The motor parameters are assumed uncertain and we only assume knowledge of their nominal values. The external load torque is also assumed to be unknown and time-varying, but bounded. Stability analysis of the output feedback system is given. Experimental results confirm the performance and robustness of the proposed controller and compare it to the cascaded proportional integral (PI) speed controller.
14 citations
TL;DR: This article shows that, with persistent excitation, the closed-loop variables are ultimately bounded and the tracking error approaches a neighborhood of zero, where the neighborhood can be made arbitrarily small via the choice of the SMC boundary-layer width parameter and the servocompensator order.
Abstract: In this article, an adaptive conditional servocompensator is proposed to achieve precise tracking control of systems with hysteresis without requiring explicit inversion of the hysteresis. Motivated by a range of applications, such as the piezoelectric-actuated nanopositioning, the system considered in this work consists of a chain of integrators preceded by a hysteresis nonlinearity modeled by a modified Prandtl–Ishlinskii (MPI) operator with uncertainty. To facilitate the proposed control design, the MPI operator is rearranged into a form comprised of three parts: a linear term, a nominal hysteretic term represented by a classical Prandtl–Ishlinskii (PI) operator, and a hysteretic perturbation. The bound on the hysteretic perturbation is further derived based on the parameter uncertainty of the MPI operator. The controller consists of two major elements. The first is a continuously implemented sliding mode controller (SMC), which exploits the bound on hysteretic perturbation and drives the system states to a bounded set in finite time. To properly “cancel” the nominal hysteresis effect without inversion, a technique involving a low-pass filter is introduced. The second element of the proposed controller is an adaptive conditional servocompensator that aims to eliminate periodic components in the tracking error. We show that, with persistent excitation, the closed-loop variables are ultimately bounded and the tracking error approaches a neighborhood of zero, where the neighborhood can be made arbitrarily small via the choice of the SMC boundary-layer width parameter and the servocompensator order. The proposed approach is implemented experimentally on a commercial nanopositioner under different types of periodic references, and it shows superior tracking performance over the traditional proportional–integral control, as well as several hysteresis inversion-based approaches reported in the literature.
13 citations
TL;DR: In this article, a load-estimator-based consensus algorithm was proposed to achieve frequency synchronization in a network of lossless, connected, and network-reduced power systems.
10 citations
TL;DR: A control strategy comprised of continuous inputs and intermittent impulsive braking inputs is presented and the feasibility of implementation of impulsive control using standard hardware is demonstrated using a rotary pendulum.
Abstract: Recent investigations of underactuated systems have demonstrated the benefits of control inputs that are impulsive in nature. Here we consider the problem of stabilization of energy level sets of underactuated systems exploiting impulsive braking. We consider systems with one passive degree-of-freedom (DOF) and the energy level set is a manifold where the active coordinates are fixed and the mechanical energy equals some desired value. A control strategy comprised of continuous inputs and intermittent impulsive braking inputs is presented. The generality of the approach is shown through simulation of a three-DOF Tiptoebot; the feasibility of implementation of impulsive control using standard hardware is demonstrated using a rotary pendulum.
3 citations