Similar model reference adaptive control with bounded control effort

Abstract

In this article, we propose an indirect similar model reference adaptive control scheme (SMRAC) in which the reference model is no longer constrained to be fixed but may be time varying in order to assure a bounded control effort, measured as the shift from the plant poles to the reference model poles. The reference model may be time varying, but its dimensionless description is kept constant; hence, the reference output, in a dimensional analysis sense, is similar. The similarity property guarantees that the dimensionless output properties of the reference model, such as the % overshoot, are kept unmodified during operation. The ideas presented in the paper allow the user to set a control effort level and the SMARC scheme maintains the control effort bounded while keeping the dimensionless properties of the reference output unaltered. This property is interesting because due to error parameter estimation and/or time-varying system parameters, the use of a fixed reference model can lead to either problems on actuator saturation or loss in achievable performance. The proposed scheme keeps the control effort bounded, while the dimensionless output properties are kept constant. The ideas presented may be extended to other adaptive control schemes.