Industrial Control Engineering

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Browsing Industrial Control Engineering by Subject "Air flow"

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    Robust Control of Industrial Boiler Using Quantitative Feedback Theory (QFT)
    (Addis Ababa University, 2019-01) Rebira, Etefa; Dereje, Shiferaw (PhD)
    Most practical Boiler systems are characterized by high uncertainty which makes them difficult to maintain good stability margins and performance properties for closed loop system. In case of conventional control, if plant parameter changes we cannot assure about the system performance. Hence it is necessary to design robust control for uncertain plant. Among the various strategies proposed to tackle this problem, Quantitative Feedback Theory (QFT) has proved its superiority especially in the face of significant parametric uncertainty. The feature of QFT is that it can take care of large parametric uncertainty along with phase (degree) and magnitude (dB) information at each working frequency. To achieve good performance of industrial boiler system which reduce fuel consumption rate and improves efficiency, dynamic variables such as fuel flow, air flow and pressure of boiler must be controlled. In the first step plant is identified by using experimental data by the mean of converting into a group of linear time invariant (LTI) uncertain plants. After representation of the uncertain dynamic system in general control configuration and modeling the parametric uncertainties, nominal performance, robust stability and robust performance against disturbances are analyzed by the concept of robust control. Finally, Linear time invariant (LTI) has been carried out and two controllers are compared. As in the PID controller case, the initial PID design balances reference tracking and disturbance rejection. In this case as well, the controller yields some overshoot in the reference-tracking response, and suppresses the input disturbance with a longer settling time. The output in response to a unit step disturbance should remain within the range [−1, 1] at all times, and it should return to 0 as quickly as possible y(t) should at least be less than 0.1 after 3 sec). From simulation we observed settling time 20.9 seconds and overshoots 30.7%. But both Controller and pre-filter controllers guarantee robust performance of the system against the uncertainties and result in desired time responses of the output variables. By applying QFT robust control, system tracks the desire reference inputs in a less time and with smoother time responses. It is observed from the simulation results that the overshoot is 0%, rising time is 0.0199 seconds and the settling time is 0.0369 seconds and Peak time is 0.0939 seconds with QFT controller. It is further observed that the proposed controller has robust stable and Performance.