The new solution bounds of the discrete algebraic Riccati equation and their applications in redundant control inputs systems

Redundant control inputs play an important part in engineering and are often used in H2$$ {H}_2 $$ control problems, dynamic control allocation, quadratic performance optimal control, and many uncertain systems. In this paper, by the equivalent form of the discrete algebraic Riccati equation (DARE), we propose new upper and lower bounds of the solution for the equivalent DARE. Compared with some existing work on this topic, the new bounds are more tighter. Next, when increasing the columns of the input matrix, we give the applications of these new upper and lower solution bounds to obtain a sufficient condition for strictly decreasing feedback controller gain. Finally, corresponding numerical examples illustrate the effectiveness of our results.