Robust LQ Control for Harmonic Reference/Disturbance Signals

Linear Quadratic (LQ) controller design is considered for continuous-time systems with harmonic signals of known frequencies and it is shown that the design is reducible to an interpolation problem. All LQ optimal loops are parametrized by a particular solution of this interpolation problem and a (free) stable/proper transfer function. The appropriate choice of this free parameter for optimal stability robustness is formulated as a multiobjective design problem and reduced to a Nevanlinna-Pick interpolation problem with some interpolation points on the boundary of the stability domain. Using a related result from the literature, it is finally shown that, if there is sufficient penalization on the power of the control input, the level of optimum stability robustness achievable with LQ optimal controllers is the same as the level of optimum stability robustness achievable by arbitrary stabilizing controllers

Generalized asymptotic regulation with guaranteed H2 performance : an LMI solution

A multi-objective controller synthesis problem is considered in which a set of generalized asymptotic regulation constraints are to be satisfied while also guaranteeing a desired level of performance measured in terms of the asymptotic variance of a performance output in response to a white noise random process with zero mean and identity covariance matrix. The generalized regulation constraints are expressed as bounds on the state-steady peak in response to disturbances generated by an anti-stable autonomous exogenous system with nonzero initial states. The controllers that guarantee these constraints can be realized by replicating the dynamics of the exogenous system within a certain structure formed by gain matrices, which are subject to convex constraints, and an accompanying controller with which the feedback loop is to be stabilized. Formulating the design of the accompanying controller in a way to guarantee the additional performance objective, the overall design is rendered tractable over a set of free variables, in terms of which the synthesis of a suitable controller is also outlined. The order of the controller is equal to the order of the plant plus the order of the exogenous system. By an adaptation of the developed techniques, a solution is also provided for the problem of generalized asymptotic regulation with suboptimal transient response