Font Size: a A A

Robust Adaptive Backstepping Control For Uncertain Nonlinear Systems

Posted on:2015-01-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:J P CaiFull Text:PDF
GTID:1268330428963567Subject:Control Science and Engineering
Abstract/Summary:PDF Full Text Request
Modeling errors, external disturbances, unmodeled dynamics are unavoidable during system modeling and its operation. All these uncertainties will deteriorate the control performance of the system, and even may lead it to instability. Therefore, such uncertainties should be taken into ac-count in system performance analysis and the controller design. Meanwhile, due to the complexity of modern large-scale system with hundreds of actuators, actuator failures are inevitable in actual applications. Such failures may lead to catastrophic accidents if there are no suitable measure to take. Recently, more and more experts and scholars in control society pay more attentions to the research on failure compensation, especially to the failure compensation of non-smooth nonlinear actuators, which has more realistic significance.In this dissertation, the lower-triangular nonlinear systems with different kinds of uncertain-ties, including non-triangular structural uncertainties and unknown failure of hysteretic actuators are considered. The uncertainties of unknown nonlinear modeling errors and unmodeled dynamics will be taken into account in the controller design. These uncertainties are always shown in un-known nonlinear functions of system states and exist in every state equation or channel, or show in mismatched form. The uncertainties can be bounded by certain known function of all sys-tem state instead of lower-triangular forms such uncertainties are called non-triangular structural uncertainties. The requirement to deal with a semi-strict feedback form of system by using ex-isting backstepping technique do no longer met. A novel robust adaptive control scheme based on backstepping is proposed for a class of nonlinear systems without lower-triangular structural uncertainties firstly. Then, two robust adaptive control schemes using backstepping technique are first proposed to compensate for the uncertain failures of hysteretic actuators of a class of nonlinear systems through backlash-like model and backlash inverse, respectively. The research results are summarized as follows,(1) Considering a class of second-order uncertain nonlinear systems with such non-triangular structural uncertainties, we present a novel backstepping-based robust adaptive control scheme, which establish the sufficient condition about the existence of controller and provide the guidelines of choosing the controller parameters.(2) A robust adaptive control scheme based on backstepping technique is presented for a class of n-order nonlinear systems with non-triangular structural uncertainties. Throughout the whole procedure in our controller design, the key point is to keep the linear relationship between the state vector x=(x1,···, xn)T and its transformed vector z=(z1,···, zn)T by adjusting virtual control αi. All effects of non-triangular structural uncertainties are accumulated to the last step for compensation by selecting appropriate control law and parameter update law. The sufficient condition about the existence of controller is also established.(3) Considering the compensation problem of unknown actuator failures of uncertain non-linear systems with hysteretic actuators, firstly, an adaptive control scheme is proposed by using backlash-like model. A discontinuous function sign(·) is included into this control law design, which result in chattering. Secondly, To avoid this phenomenon, a series of smooth functions are used to approximate the function sign(·) in the control law. The stability of closed-loop system can be ensured by the adaptive controllers and the performance of closed-loop system has been improved greatly.(4) Considering a class of uncertain nonlinear systems preceded by m hysteretic actuators which exhibit unknown backlash nonlinearity and possibly experience unknown failures, an adap-tive backstepping compensation control scheme is proposed based on smooth inverse of the actua-tor backlash. Due to the fully utilization of backlash structure information in controller design, the performances of closed-loop system have been greatly improved.
Keywords/Search Tags:nonlinear system, adaptive control, backstepping, modeling error, backlash hystere-sis, actuator failure
PDF Full Text Request
Related items