Robust control of a 1.5 MW free turbine with complex load: nonlinear closed loop simulations

This paper describes the results of nonlinear closed loop simulations of a 1.5 MW free turbine with complex load. The nonlinear model is developed within SIMULINK from details previously presented by Biss and Grimble (1993). The generalised H_infinity (GH_infinity ) and classical controllers, implemented within the paper, were previously designed and applied in the above paper to linearised models of the engine. The performance of the controllers when applied to a nonlinear model in the presence of a severe load disturbance are compared with the predictions of the linear closed loop simulations discussed in the above paper. The nonlinear model includes constraints on the magnitude of the manipulated variable. The results show that the GH_infinity controllers provide better disturbance attenuation than the classical controllers in the absence of manipulated variable constraints, as predicted by the linear simulations. However when the range of the manipulated variable is limited in some cases the GH_infinity controlled system becomes unstable whereas the classical controllers are still able to satisfy the majority of the performance requirements.