Behavior Responses and Control Modeling Based Cascaded Pid Controller Scheme for Combustion of a Utility Boiler

Abstract – The main objective of the combustion controller in a thermal power plant is to regulate fuel and air in proper ratio to maintain the desired steam pressure at the turbine inlet, irrespective of the changes in steam demand. To achieve a continuous supply of steam at the desired pressure conditions is difficult to cope with inherent time delay, nonlinearity due to uncertainty of the combustion process and frequent load changes. This paper deals with the design of behavior response computation based approach to get the optimal PID controller parameters for the combustion control of utility boiler. A separate control model is developed for Fuel and Air system. The control model for fuel will drive the Fuel controller which is cascaded with Air controller. PID controller for Air and Fuel system will use the optimum PID parameter derived from response based computation method. Many steady state and dynamic behavioral responses were analyzed for different load conditions. A lab scale experimental setup is fabricated in the laboratory for fuel and air control and tests were carried out for several load conditions. Optimal PID controller parameters were obtained when the experimental responses have good agreement with the real time behavior responses. The advantages of the proposed design are highlighted.