Global stabilisation of input-saturated systems subject to L-2 disturbances

Globally stable control of linear systems with input saturation subject to L-2 disturbances is analysed. The well known results on disturbance-free systems are that nonlinear controls can ensure global stability, while linear time-invariant controls can only achieve semiglobal stabilisation. A linear control with a tuning parameter is proposed to achieve global stability of the systems even when they are subject to arbitrary L-2 disturbances. The parameter is automatically tuned using a switch rule based on state measurement. The advantage over the existing algorithms is that no online solution of algebraic Riccati equations is needed. Control design of an armature-controlled DC servomotor is used to demonstrate the proposed algorithm, and simulation results are shown.