Turbo Expander System Behavior Improvement Using an Adaptive Fuzzy PID Controller.

Turboexpanders are used in industries for cooling, liquefaction and also power generation. An important part of these turbines is the variable angle nozzlecausing a nonlinear behavior that is not well recognized among the prime movers of the dispersed generators. In this paper, at first, the turbo expander system is evaluated in detail and its nonlinear behavior is investigated. Then, the system is linearized and the variations of its eigenvalues are investigated by a system modal analysis for some changes in input gas stream parameters. Afterwards, the variations of nozzle angle and output pressure are studied using a conventional PID controller. Due to the system nonlinearity, adaptive PID and fuzzy controllers are then designed to improve the system behavior by controlling mechanical parts of turbine nozzle actuator. An adaptive controller uses a fuzzy system as a nonlinear tuner to specify the coefficients for conventional PID controller of the system. A comparison of controllers’ effects is presented. Simulation results show that the turbine response to step changes in gas flow rate or pressure would be steadier when the adaptive or fuzzy controllers are used.