Optimal power control of a three-shaft brayton cycle based power conversion unit

This paper discusses the development of a control system that optimally controls the power output of a Brayton-cycle based power conversion unit. The original three shaft design of the Pebble Bed Modular Reactor (PBMR) power plant is considered. The power output of the system can be manipulated by changing the helium inventory to the gas cycle. The helium inventory can be manipulated in four ways: Injecting helium at the high-pressure side of the system by means of a booster tank; extracting helium at the high-pressure side of the system; injecting helium at the low- pressure side of the system and lastly opening and closing the bypass control valve. The control system has to intelligently generate set point values for each of the four helium manipulation mechanisms to eventually control the power output. In this paper two control strategies are investigated namely PID control and Fuzzy PID (FPID) control. The FPID control strategy is a linear type Fuzzy controller, but can progressively be made nonlinear if nonlinearities exist in the system. An optimal control system is derived by applying an optimisation technique to the gain constants of the controllers. A Genetic Algorithm (GA) is used to optimise the gain constants of both the PID and FPID controllers. The GA uses the ITAE performance index as an objective function.