Continuous order identification of PHWR models under step-back for the design of hyper-damped power tracking controller with enhanced reactor safety

Highlights: ► Discrete time integer order transfer function models of a PHWR have been identified. ► Frequency domain data of LSE based identified models are used for FO model building. ► FO models with small commensurate order can be considered as continuous order models. ► CTCO PID controller places all closed loop reactor poles in higher Riemann sheets. ► Hyper-damped control system ensures higher safety margin for reactor operation. -- Abstract: In this paper, discrete time higher integer order linear transfer function models have been identified first for a 500 MWe Pressurized Heavy Water Reactor (PHWR) which has highly nonlinear dynamical nature. Linear discrete time models of the nonlinear nuclear reactor have been identified around eight different operating points (power reduction or step-back conditions) with least square estimator (LSE) and its four variants. From the synthetic frequency domain data of these identified discrete time models, fractional order (FO) models with sampled continuous order distribution are identified for the nuclear reactor. This enables design of continuous order Proportional–Integral–Derivative (PID) like compensators in the complex w-plane for global power tracking at a wide range of operating conditions. Modeling of the PHWR is attempted with various levels of discrete commensurate-orders and the achievable accuracies are also elucidated along with the hidden issues, regarding modeling and controller design. Credible simulation studies are presented to show the effectiveness of the proposed reactor modeling and power level controller design. The controller pushes the reactor poles in higher Riemann sheets and thus makes the closed loop system hyper-damped which ensures safer reactor operation at varying dc-gain while making the power tracking temporal response slightly sluggish; but ensuring greater safety margin