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9. Final conclusions
THE METHOD
Frequency domain controller regulation is a well established technique in the automation and electronic engineering field. It has already proved its utility in thermal hydraulics in the case of Rzf. [2] and also in this study case.
In fact it has been possible to highlight the dynamics of the process to control, and it provided a driving criteria (the stability margins) to optimize the regulations and quantify their stability. In this sense it allowed not to make a “blind” choice of the configuration also when no detailed requirements where placed on the control system.
The choice of a 0-D model proved to be very useful in reducing calculation time. Even if the details provided by a CFD analysis have been lost, time gained allowed to perform sensitivity studies on the system. It is in this way that the impact of the lost details has been limited.
THE SOFTWARE
The chosen software environment has proved to be very powerful. The software fulfilled all the expectations about it and it was possible to perform and conclude all the stages of the study on the same software platform without any particular difficulties.
The Control System toolbox provides also a time simulation based on the linearized model and this simulation was in good accordance with the results provided by the simulation in the time domain. This demonstrates that:
̶ The choice of the operating point was representative of the state of the system in the real operating condition;
̶ The accuracy of the algorithm used by the software to linearize the model.
Moreover predictions about the stability of the closed loop where always respected when validating the configuration in the time domain by means of a Simulink® simulation.
The main advantages of having used the Matlab®/Simulink® software (an its related add-on Control System toolbox) have come from:
147 ̶ The graphic interface that accompanies either Simulink® either the “Control System
toolbox”;
̶ The high integration of its toolboxes;
̶ The possibility to work on only one time domain built model to perform frequency analysis, controller tuning and, at the end, time validation of the controller.
One negative aspect is the complexity that the model attains when the Simulink® “real objects” library (Simscape add-on) is not available: in fact it has been necessary to implement the equation (or the set of equations) that describes each component using the basic Simulink® library (mathematical and logic functions). This can be time consuming since it requires a stage of theoretical analysis.
CONCLUDING REMARK
Further attention is going to be paid on the software and on the frequency analysis of systems and on the implications and benefits that they could have in design procedures.
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References
[1] Areva’s internal documentation;
[2] “The Thermal-hydraulics of a boiling water nuclear reactor – 2nd ed.” (Chapter 7: Boiling Water Reactor stability analysis) – R.T. Lahey Jr; F.J. Moody; ANS (American Nuclear Society).
