Output feedback Cross-Coupled Nonlinear PID based MIMO control scheme for Pressurized Heavy Water Reactor

Abstract

The dynamics of Pressurized Heavy Water Reactor (PHWR) are complex and open-loop unstable in nature. In such systems, parametric and input disturbances may cause instability if the control system fails to reject these disturbances. For such a large, unstable and uncertain process, designing a control scheme with the ability to reject disturbances along with good reference tracking capabilities is a challenging problem. The control scheme should not only be robust but also deterministic and easier to implement. In order to fulfill all these control scheme requirements for nuclear industries, in this work, a Cross-Coupled Nonlinear Proportional Integral Derivative (CCN-PID) scheme is suggested for a 70th order Multi-Input Multi-Output (MIMO) PHWR. It is also shown in this work that the proposed CCN-PID is a simple Cross-Coupled Proportional, Nonlinear Integrator and Derivative (CC-PNID) sliding surface based Sliding Mode Control (SMC). Furthermore, for the output feedback design, a High Gain Observer (HGO) is constructed for the PHWR process. In order to assure robust stability of the closed loop system, a Lyapunov based analysis of the state feedback CCN-PID control scheme is firstly presented. Then, in a similar way, robust stability analysis of HGO is carried out and finally, the stability analysis of the HGO and CCN-PID based output feedback control scheme is evaluated. In order to investigate the performance of the designed HGO based output feedback CCN-PID control scheme, four different scenarios are simulated. The results of these simulations show that the suggested control scheme efficiently rejects parametric uncertainties and input disturbances and corrects the power tilts while keeping the reactor stable and within safe limits of operation. The results also show that the scheme controls the reactor in an effective manner such that the reactor power closely follows the reference signal. The results of the control scheme presented in this work are also compared with earlier works.