Faculty Publications

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Author: search.filters.author.Sankar Rao, C.S.Subject: search.filters.subject.Controllers

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    Robust decentralized proportional–integral controller design for an activated sludge process
    (John Wiley and Sons Ltd, 2020) Anchan, S.S.; Sankar Rao, C.S.
    This paper presents the design of a decentralized proportional–integral (PI) controller for a wastewater treatment plant (WWTP). The aeration rate and the return recycle sludge rate are manipulated inputs to the WWTP process, while substrate and biomass concentration are considered as the output variables. The study is divided into two segments: A decentralized controller is designed based on the best pairing in the first segment, and in the second segment, a decoupler is developed to reduce the interactions. Decouplers are generally used to create independent loops in the multivariable control loops. Each decoupled subsystem is converted to first order plus time delay (FOPTD) model using a system identification toolbox to design independent diagonal controllers. The numerical simulations have been performed to evaluate the effectiveness of the presented methods. Furthermore, a robustness study has also been carried out by taking into account multiplicative input and output uncertainties, and it is found that the controller designed based on minimizing the integral of absolute error (IAE) criteria shows more robust. © 2020 Curtin University and John Wiley & Sons, Ltd.
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    Simultaneous separation of ternary mixture using modified dual compression middle vessel batch distillation column: Control and dynamic optimization
    (Taiwan Institute of Chemical Engineers, 2022) Desikan, B.; Krishna, P.; Sankar Rao, C.S.
    Background: Multivessel batch distillation has been found to be an effective method for the separation of multi-component mixtures. In this article, an effort has been made to devise a fast middle vessel batch distillation column (MVBDC) for the ternary separation of an Ethanol/Propanol/Butanol mixture by the means of inducing vapor compression in the system. Methods: ASPEN PLUS V12 has been used to generate the initial steady-state flowsheet of the process for equipment sizing. In contrast, ASPEN Dynamics was used to evaluate the performance of the batch distillation with various control structures and to perform a dynamic optimization on the proposed batch distillation column. MATLAB was used to identify single-input single-output transfer functions for more effective PID controller tuning. Significant Findings: The proposed Middle vessel batch distillation was found to separate each component of the mixture to a purity of 99 mol% in 22 h (for the cascade control structures) and 21.73 h (for the temperature control structure). This was found to be significantly lesser than the batch time of a conventional batch distillation column (28.12 h), while the energy consumed by the proposed column was 3.4 MMkcal lesser than the energy consumed by the conventional column. Dynamic optimization further reduced the batch time by 14.4% while simultaneously reducing the energy consumed by 20.3%. © 2022 Taiwan Institute of Chemical Engineers
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    Centralized Proportional Integral Controller Design for the Activated Sludge Process
    (John Wiley and Sons Inc, 2022) Anchan, S.S.; Sankar Rao, C.S.
    The design of a centralized proportional integral controller for a single-tank activated sludge process is presented. The relative normalized gain array (RNGA) and dynamic relative gain array (dRGA) were adopted for enhancing the closed-loop performance of a multivariable system. The dRGA method gave superior and acceptable responses compared to the RNGA method. The designated error indices decreased significantly for the dRGA method compared with the RNGA method. The dRGA method is simple and effective, since it considers the process dynamics to provide an accurate interaction assessment. The designed centralized controller overcomes the limitations of the decoupler for stability challenges when compared with decentralized controllers. © 2022 Wiley-VCH GmbH.
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    A Simple Method to Design a Decoupler for a Proton Exchange Membrane Fuel Cell
    (John Wiley and Sons Inc, 2022) Goyal, I.; Reddy, S.; Sankar Rao, C.S.
    A decoupling control system is designed by a simple tuning-free method for the multi-input multi-output model of a proton exchange membrane fuel cell. The decoupler minimizes the interactions among the loops and is designed by estimating the relative normalized gain array and dynamic relative gain array for the closed-loop model. The proportional integral controller settings are estimated using the partial model matching method. The performances of the proposed method are studied based on closed-loop performances of control variables and time integral errors that are compared with the synthesis method. The proposed controller performs better in terms of integral of time-weighted absolute error. © 2022 Wiley-VCH GmbH.
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    Optimal detuning of multivariable proportional integral controller based on data-driven approach for an activated sludge process
    (John Wiley and Sons Ltd, 2023) Anchan, S.S.; Kumar Tanneru, H.; Sankar Rao, C.S.
    The study deals with designing a multivariable centralized proportional-integral (PI) controller for an activated sludge process (ASP) by adopting a new tuning technique. To overcome the tedious task of manual tuning by a classical method that was based on Ziegler–Nichols tuning, a novel approach is developed by formulating the optimization problem and considering it along with the theoretical results to calculate the controller parameters. The proposed method is then compared with the reported method to demonstrate the advantages of the proposed approach. A nonlinear ASP model is selected to evaluate the performance of the designed controller. The simulation carried through the proposed optimization technique exhibits a significant improvement in closed-loop performance for tuning the centralized controller. It is observed that the proposed method minimizes the effort of tuning the controller significantly. The proposed controller achieves better load disturbance response and lower overshoot than the reported method. The proposed method could improve integral absolute error (IAE) and integral time absolute error (ITAE) performance indices, ranging between 18.69% to 53.80% and 16.42% to 52.97% for a step change in (Figure presented.) and (Figure presented.), respectively, which are better compared to the reported method. The study also assesses the control system's robustness for their uncertainties with the time constant and time delay. © 2023 Curtin University and John Wiley & Sons Ltd.