Nonlinear robust control for single-machine infinite-bus power systems with input saturation

Abstract

Abstract. In this paper, a new control scheme is proposed to achieve stability for a single-machine infinite-bus power system. A power system model simultaneously considering input saturation and time-varying uncertainties is presented. A sufficient condition for the system convergence is given and based on this result, a switching excitation control law with auxiliary system is designed. The stability analysis and simulation results all show that the developed controller is effective.Key words: nonlinear robust control, input saturation, generator excitation, single-machine infinite-bus power systems (SMIB).Nonlinear robust control for single-machine infinite-bus power systems with input saturation Y. WAN * College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China tion to the control problem of nonlinear systems with input saturation. In [9], an auxiliary system is employed to address input constraints, but only boundedness of the "last modified virtual error" is obtained. If the desired value of control input greatly exceeds the constraints, then the auxiliary system will be unstable and thus the convergence of the "last virtual error" to the origin cannot be ensured. In [10], the tanh function and the mean-value theorem are used to deal with the saturation function, and then the redial basis function i.e. neural network is employed to approximate the unknown control gain. However, since the tanh function is also a kind of bounded function, when there are large disturbances and the desired value of control input goes beyond the range of tanh, the efficacy of the designed control law may be limited. In [11], dynamic surface control is used to equivalently transform a class of nonlinear system into a linear system, and then the region of attraction which is enlarged to allow some degree of input saturation is estimated via a linear matrix inequality method [12]. But this approach does not give a solution for a case when the initial condition is out of this region of attraction. This article proposes a new nonlinear robust control framework to tackle the stabilization problem for a class of nonlinear system with time-varying uncertainties and input saturation. Compared with the prior works, the proposed method ensures not only the boundedness of state variables but the global stability of the closed-loop system. Furthermore, the approach proposed processes the saturation phenomenon directly and does not require approximating the saturation function by a smooth function, which is often not invertible outside its range.The paper is organized as follows: the preliminaries and a SMIB power system model are described in Section 2. In Section 3, a sufficient condition for the convergence of states to the origin under saturation is shown in a Theorem, and then on the basis of this result, a switching excitation control law with auxiliary system (SAEC) is designed, as well as stability analysis for the closed-loop system with the designed controller. The simulation resul...