Optimal LPV control with hard constraints

This paper considers the optimal control of polytopic, discrete-time linear parameter varying (LPV) systems with a guaranteed ℓ₂ to ℓ_∞ gain. Additionally, to guarantee robust stability of the closed-loop system under parameter variations, H_∞ performance criterion is also considered as well. Controllers with a guaranteed ℓ₂ to ℓ_∞ gain and a guaranteed H_∞ performance (ℓ₂ to ℓ₂ gain) are a special family of mixed H₂=H_∞ controllers. Normally, H₂ controllers are obtained by considering a quadratic cost function that balances the output performance with the control input needed to achieve that performance. However, to obtain an optimal controller with a guaranteed ℓ₂ to ℓ_∞ gain (closely related to the physical performance constraint), the cost function used in the H₂ control synthesis minimizes the control input subject to maximal singular-value performance constraints on the output. This problem can be efficiently solved by a convex optimization with linear matrix inequality (LMI) constraints. The main contribution of this paper is the characterization of the control synthesis LMIs used to obtain an LPV controller with a guaranteed ℓ₂ to ℓ_∞ gain and >H_∞ performance. A numerical example is presented to demonstrate the effectiveness of the convex optimization.