Analysis of Model Uncertainties Using Inverse Simulation

摘要

Helicopter modelling is a complex task as helicopters consist of many subsystems (nacelle, rotor, engine,u0001 u0001 u0001 ) that arerndescribed by coupled differential equations. Controller design requires a model that is accurate over a certain frequencyrnrange. Usually, system identification is used to derive the models from flight test data and the model complexityrndepends on the frequency range of interest. Since system identification is an empirical process and the measuredrndata are approximated by low-order equivalent models, high modelling accuracy is not self-evident. To assist systemrnidentification, inverse simulation is applied. This type of simulation computes control inputs needed to obtain thernmeasured output variables. The comparison of measured and inverse simulated control inputs provides an additionalrntool for model validation. In this paper, inverse simulation is applied to identified matrices of the EC135 ACT/FHS.rnThe results show that the model uncertainties can be subdivided into deterministic and stochastic ones. Finally therndeterministic modelling errors are described by generic transfer functions which can be used as disturbance input intornthe plant for controller design.