International Journal of Control, Vol.83, No.8, 1664-1673, 2010
LMI-based H-optimal control with transients
In this article, the worst-case norm of the regulated output over all exogenous signals and initial states as a performance measure of the system is characterised in terms of linear matrix inequalities (LMIs). Optimal time-invariant state- and output-feedback controllers are synthesised as minimising this performance measure. The essential role in this synthesis plays a weighting matrix reflecting the relative importance of the uncertainty in the initial state contrary to the uncertainty in the exogenous signal. H-optimal control with transients is shown to be actually a trade-off between H-control, being optimal under unknown exogenous disturbances and zero initial state, and -control, being optimal under zero exogenous signal and unknown initial conditions, if and only if the weighting matrix satisfies a fundamental inequality. If this inequality is met, the performance measure is achieved and the explicit formulae for the worst-case disturbance and initial state are provided. If this inequality fails, the performance measure coincides with the H-norm and the trade-off gets broken.
Keywords:H control;unknown initial conditions;linear quadratic control;linear matrix inequality;output-feedback controller