Hybrid modelling and control of a power plant three-stage reheater

The problem of modeling and control of a three-stage steam reheating process in a steam power plant is considered in this paper. Mathematical model of this process is marked by considerable nonlinearity. Moreover, switching of dynamic behavior occurs because individual reheat stages are bypassed depending on the value of manipulated variable. For both of these reasons, there is a little chance that replacing the traditional control system based on cascade PID/PI loops with advanced control methods such as MPC based on single linearized model may bring any performance improvement. However, both of these features make the steam reheating process a suitable object of modeling with a hybrid model in the form of a switched piecewise affine (PWA) system. Hybrid MPC based on this model then becomes a promising candidate approach to control. This paper describes the results of PWA modeling of the steam reheating process. A good agreement of responses between PWA model and nonlinear first principles model is shown. Following the development of this model, the design of a hybrid MPC controller is outlined.