Nonlinear control of conventional steam power plant

Abstract

Conventional fossil fueled power plants are the leading power producers despite the existence of other energy sources and power generation technologies. As renewable power production is integrated into the grid, the operation of the conventional power plants faces new challenges that demand new control strategies. A key challenge is that the power demanded from conventional plants will continuously change to recover the production shortages caused by the intermittency of the renewable sources. This challenge demands an efficient control structure that is able to accommodate such power fluctuations, in addition to the inherent complexities of power plants such as the existence of deadtime associated with solid fuels. Coal, for example, is pulverized in real time prior to being transported to the furnace, which in turn, introduces deadtime to the power generation process. This thesis proposes the use of deadtime compensated nonlinear controllers that are based on feedback linearization of models obtained from physical principles for the control of coal fired power plants. The designed control strategies aim to control power generation, boiler pressure, boiler drum level, and superheated and reheated steam temperatures. In the first part of this thesis, the control of the boiler pressure and power generation is considered. A single deadtime compensated model state feedback structure is developed to track variations in power demand and to reject applied disturbances. The second part focuses on the development of a control strategy for the drum level dynamics in addition to the boiler pressure and power generation. The strategy proposed aims to decouple the manipulated variables of the boiler pressure and the drum level dynamics and applies a conventional three-element level controller with the deadtime nonlinear controller proposed in the first part. In the last part of the thesis, the control of the boiler pressure, power generation, superheated steam temperatures is considered. The control strategy considers decoupling the performance of the boiler from the superheated steam temperature, the decomposition of the overall plant into three cascading subsystems and the application of deadtime compensated nonlinear controller for each subsystem.