The conventional approach to Rolls-Royce Inverse Model closed loop fuel control is to represent the inverse high-pressure (HP) spool dynamics within the controller. In this paper, the options of configuring the controller to represent either the intermediate (IP) or the low pressure (LP) dynamics of a 3-spool engine are also analysed. Control performance is assessed as the engine is subjected to step changes in power offtake. For each controller, power offtake is extracted from each of the three shafts in turn giving a total of 9 engine/controller configurations. For any given power offtake configuration applied to the engine, the results suggest that the controller based upon LP or IP dynamics offers more robustness measured in terms of phase margins and improved performance with regard to power offtake disturbance rejection.

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