Second-order sliding mode fault-tolerant control of heat recovery steam generator boiler in combined cycle power plants

Power generation plants are intrinsically complex systems due to their numerous internal components. Higher energy efficiency in power plants is now achieved through employing combined cycles. In this article, an adaptive robust Sliding Mode Controller (SMC) is designed to overcome the faults in Heat Recovery Steam Generator boilers (HRSG boilers) as one of the main parts of a combined cycle plant. On condition that a fault occurs in the HRSG boiler, the control system must be able to reconfigure its parameters to maintain the admissible thresholds in dynamic variables such as drum pressure, steam temperature, and drum water level. To achieve good performance for the boiler, the proposed adaptive robust SMC shall conquer the effects of faults and uncertainties by estimating their upper bounds adaptively, and force the outputs of the multivariable boiler to track the outputs of a desired multivariable reference model. Manipulating a suitable control input and using second-order sliding mode control strategy, the output tracking error slides to zero on a PID sliding surface. Besides tracking, the controlled boiler tolerates faults in system matrix, faults in input matrix, and external disturbance signal. Numerical simulations confirm the effectiveness of the proposed FTC (Fault-Tolerant Control) system for an uncertain non-minimum phase HRSG boiler.