Study On Sliding Mode Variable Power-Level Control Method For Pressurized Water Reactors

Power-level control technique is one of the key techniques guaranteeing safe,stable and efficient operation of nuclear power plants.Along with the growing proportion of nuclear power in the total electricity generation,nuclear power units need to participate in the power grid peak shaving urgently.In order to improve the stability and economic efficiency of the power grid,nuclear power plants should have the capability to make power changes according to the grid requirements,i.e.the load tracking capability.Because nuclear power plants are in nature of highly complex,time lag and nonlinear systems,there is still large space for classic PID controllers to get a better performance,especially when large load variation occurs.The variable structure control method has the characteristics of simple structure,fast response,and strong robustness against external disturbance.It has an important significance to apply the variable structure control theories to power-level control problems for pressurized water reactors.First,the various influence factors of the reactivity during load tracking process are analyzed.The differential time domain model and state space mode which can describe the power-level control process are established based on lumped parameter method.To solve the problem that parts of the state variables such as,the relative concentration of delayed neutron precursor and the average fuel temperature cannot be measured,a state observer based on sliding mode method is introduced to observe and obtain their estimation value.The sliding mode controller which contains a nonlinear sliding mode surface and a reaching law is designed to track the load change of the pressurized water reactors.Moreover,the impacts of different reaching law on controlling effect are analyzed.Based on the above work,for the case that the power-level control model for pressurized water reactors exist uncertainty factors,a series connection extended state observer is introduced to observe and obtain the estimation value of the unmeasured state variables and the uncertainty parameters.To guarantee the reaching quality during the sliding mode control process,an improved reaching law is designed and its dynamic performance is analyzed theoretically,and a sliding mode controller based on improved sliding mode algorithm is presented to track the load change of the pressurized water reactors,moreover,advantages and disadvantages of this improved reaching law on controlling effect are analyzed.Finally,the fuzzy control algorithm and the sliding mode control algorithm are combined,and the parameters of the reaching law are self-adjusted by fuzzy rules in order to guarantee the best reaching quality.After that,the chattering phenomenon is weakened,and the control performance is improved.The globally asymptotic closed-loop stability analysis of the designed control systems is given by Lyapunov stability criterion,and the feasibility of those controllers is proved through numerical simulations.