When a failure occurs in a nuclear plant, a lack in the response of the controller could lead to serious consequences. The fundamental property to be ensured by the controller is the plant stability, possibly proved formally, and at least in the range of validity of the process model. In this work, using a mathematical model for the primary circuit of a PWR, accurate enough to catch the nonlinear, time–varying, and switching nature of the system, and suitable for the control purposes, the reactor power controller, the inventory controller for the primary circuit, and the pressurizer pressure controllers are designed. These controllers do not use direct measurements of the pressurizer pressure or temperature, but they use instead pressurizer wall temperature measurements. Disturbances and parameter variations are compensated by the use of sliding–mode terms, which guarantee further robustness to the control scheme. The switching nature of the controller, reflecting the switching nature of the pressurizer dynamics, and the nonlinear terms implemented in the controllers, along with classical PI actions, ensure better transient behaviors. Hence, they represent an evolution and an improvement with respect to classical PID controllers, usually implemented in standard control actions.

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