Robust Fixed-Time Integral Sliding Mode Control of a Nonlinear Hydraulic Turbine Regulating System

The hydraulic turbine regulating system (HTRS) plays an important role in the safe and stable operation of hydropower stations. In this paper, a fixed-time integral sliding mode controller (FTISMC) is designed to make the nonlinear HTRS with disturbances stable in a fixed time. The HTRS is a highly complex, strongly coupled, nonlinear nonminimum phase system, which can ensure the frequency and rotor angle of generator stability by adjusting the guide vane opening. In order to decouple the nonlinear HTRS, the input/output feedback linearization is applied to establish the relationship between the control input and the output of the HTRS. Based on sliding mode control (SMC) theory and fixed-time stability theory, FTISMC is proposed to stabilize the HTRS in a fixed time. Compared with the finite time control method (FTCM), the convergence time of nonlinear HTRS under FTISMC is independent of initial conditions and can be exactly estimated. Meanwhile, the integral sliding surface can avoid singularity, thus eliminating the chattering phenomenon. Finally, the numerical simulation is implemented to demonstrate the superior performances of the proposed FTISMC than the existing PID, SMC, and FTMC.