Measurement and identification of gas turbine dynamics in the presence of noise and nonlinearities

The identification of the fuel flow to shaft speed dynamics of a two shaft gas turbine engine is addressed. The measurement problem is discussed along with the limitations of previous work. The paper discusses why a measured input signal must be used for identification and why poor time domain models are consequently obtained, caused by the violation of the zero order hold assumption on the input. Frequency domain identification, using multisine test signals, is shown to overcome these problems and produce high quality models. The tests also yield information on the levels of nonlinearity and noise and the duration of pure time delay. This work illustrates the potential of frequency domain techniques for modelling systems which are difficult to model using time domain methods.