Nonlinear power-level control design for MHTGRs by considering stepper motor dynamics

• Stepper motor for driving control rods deeply influences MHTGR's operation.
• An MHTGR power-level control is given by considering stepper motor dynamics.
• This control can guarantee globally asymptotic closed-loop stability.
• Numerical simulation results show the feasibility of this control.

Due to its inherent nuclear safety, modular high temperature gas-cooled reactor (MHTGR) is promising in building the next generation nuclear plants which provide safe and clean power or heat supply. It is clear that power-level control technique is crucial in guaranteeing safe, stable and efficient operation of MHTGRs. Since MHTGR dynamics is complexly nonlinear, it is necessary to develop nonlinear power-level control laws. The stepper motor is a satisfactory choice for driving the control rods of MHTGRs, and has already been applied to under-construction HTR-PM plant. Since a stepper motor itself is a nonlinear dynamic system that can deeply influence power-level control performance, it is meaningful to develop nonlinear power-level control laws of MHTGRs by considering the stepper motor dynamics. Motivated by this and based upon the backstepping technique and physically-based control design approach, a novel nonlinear power-level control is proposed by regarding the MHTGR and stepper motor as an entire dynamical system. It is proved theoretically that this newly-built power-level controller can guarantee globally asymptotic closed-loop stability by generating proper motor stator voltages. Numerical simulation results show not only the feasibility of this novel control law but also the relationship between regulation performance and controller parameters.