H∞ ANALYSIS AND SYNTHESIS BY GENETIC ALGORITHMS OF THE ATTITUDE CONTROL SYSTEM OF THE BRAZILIAN SATELLITE LAUNCHER

摘要

This paper introduces approaches for H∞ analysis of thernattitude control system of the Brazilian satelliternlauncher (VLS), to attenuate the bending modesrneffects. This study firstly shows that the effect ofrnintroducing a band-reject (notch) filter is similar to thatrnproduced by the use of an H∞ controller synthesized tornreject flexible dynamics. Next, the proposed H∞rnanalysis indicates that the filter-switching manoeuvre,rnnecessary to ensure stability at the time of therntransition from the first to the second stages, should bernperformed earlier to get better results in terms ofrnattenuation of the considered oscillation modes. Then,rntime evolutions of the H∞ norm of the closed-looprnflexible dynamics channel pointed out thosernimprovements in time and frequency performances arernpossible if the parameters of the filter are scheduledrnduring the atmospheric flight. The classicrnmethodology uses a controller with a Proportional-rnIntegral-Derivative (PID) structure. The gains arernadjusted through the linear-quadratic (LQ) controlrntechnique in order to accomplish stationaryrnperformance requirements. This paper also introducesrnapproaches for synthesis of a set of correspondingrnrobust PID controllers, by genetic algorithms (GA). Arnnew design methodology resulted satisfactory, takingrncare of the performance restrictions, structure andrnnumerical variations of the gains. As a result, a set ofrncorresponding robust PID controllers was obtained andrntested.