Stability region of closed-loop pilot-vehicle system for fly-by-wire aircraft with limited actuator rate
Keywords:pilot induced oscillation, rate limited actuator, closed-loop pilot-vehicle system, stability regions, linear matrix inequality
AbstractThe category-II PIO (Pilot Induced Oscillations) caused by actuator rate limitation of fly-by-wire airplanes will badly threaten the flight safety. The stability regions of closed-loop pilot-vehicle (CLPV) system with rate limited actuator were studied in this paper to assess stability of such CLPV system. The augmented state variables were introduced to segregate the rate limited element from the primary system in order to build the saturation nonlinear model of CLPV system. To get the maximal stability region, firstly, the estimation of the stability region of CLPV system is transformed into convex optimization problem; secondly, the Schur complement lemma is applied to transform the convex optimization problem intolinear matrix inequalities(LMIs) formulations; finally, the ellipsoidal stability region estimation algorithm is obtained. The time-domain simulation results show that the estimated stability region is slightly conservative and within the real stability region of CLPV system. The category II PIO of static unstable fly-by-wire airplanes is a kind of much rapid divergent oscillation instead of limit cycle oscillation. Moreover, the stability region is distinctly influenced by the pilot controlling gains and the actuator rate limitation value, the proposed stability region method exhibits clear physical concept and intuitionistic results.
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