Control structure analysis and design for boiler-turbine units

Based on a low-order nonlinear model of a boiler-turbine unit, a simplified general model which can capture the essential dynamics and interaction of a unit is derived in this paper. The control structure of this model is analyzed via the decentralized relative gain method (dRG) under the condition of finite-bandwidth control. Then internal model control (IMC) principle is applied to design the decentralized PID controllers. When the coupling is strong and the fully decentralized structure can not meet the desired performance, Gramian method is applied to analyze the partially decentralized structure of the model, and the resulting controller is tuned based on the decentralized and the centralized controller. Simulation results show that partially decentralized controller can achieve comparable performance as the centralized one; however, it has a simpler structure and is easier to implement and tune.