Case study comparison of robust linear quadratic design and mixed-sensitivity H∞ control

The aim of the paper is to compare the respective advantages of time-domain robust linear quadratic and frequency-domain H_∞ control laws in the presence of real parametric and frequency-dependent uncertainties. Design-application considerations for each method are also offered. For the time-domain design, the LQL method is used, which is a minimax robust state estimation-maximin state feedback closed-loop control scheme for linear systems with L₂ bounded uncertainties. For comparison, the frequency-domain mixed-sensitivity H_∞ approach is also examined. To improve its poor parametric robustness owing to LHP pole-zero cancellation property of H_∞ controllers, increasing system bandwidth and inner-loop feedback enhancing the damping are applied simultaneously. The context of this design comparison is the HIT-3T2 flight simulator. The simulation results, once again, reveal the close relationship of LQL and H_∞ control synthesis on the basis of game theory