Sliding Mode Control of Gas Turbines Using Multirate-Output Feedback

The advent of electronic controllers in the field of gas turbine control has allowed the implementation of sophisticated control algorithms. The design of a control system requires accurate models of the plant to be controlled. A real-time program for the dynamic simulation of a gas turbine engine has been developed. Most of the control design techniques need the linear representation of a plant at various operating points. In this regard, the linear analysis tool box of MATLAB-SIMULINK (Anon., 2004, SIMULINK: User’s Guide, The Math Works, Inc.) has been used to obtain linear models at various operating points. The linear models are discretized at various sampling times. The algorithm for discrete sliding mode control using the output samples has been reviewed and the same has been used to develop a controller for the gas turbine engine. A fast output sampling sliding mode controller is synthesized using a linear model of the engine. The controller developed is implemented in the nonlinear model and simulation with external disturbance is carried out. The responses with and without the controller are compared. It is shown that discrete sliding mode control law can be directly obtained in terms of the output samples and immediate past control function. The control law thus obtained is of practical importance. The algorithm needs the states of the system neither for feedback purpose nor for switching function evaluation. Thus, it is easily implemented in practice. The algorithm is computationally simple and easy to implement on a gas turbine.