Articles written in Sadhana

    • Exponential state observer based finite time control of fully active hybrid energy storage system


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      This paper suggests an observer based control approach for fully active hybrid energy storage system (HESS) comprising of two storage elements such as supercapacitor (SC) and battery, two bidirectional DC–DC converters and variable load. In order to formulate a control approach for this hybrid system, theunmeasured dynamics of the system must be available. This engenders the design of a robust exponential state observer in this paper to estimate various unknown system variables such as load, battery and SC currents/ voltages. Furthermore, this paper also renders an integral terminal sliding mode control (ITSMC) concatenated with Proportional Integral (PI) based Lyapunov’s function technique to robustly track the reference battery current, SC current and load voltage in finite time in the presence of lumped system uncertainties. Therobustness, stability and finite time convergence properties of the closed loop system with the proposed technique are demonstrated through analytical approach. Simulated results are validated with the proposed methodology through various case studies and compared with LMI (linear matrix inequalities) based robust control techniques presented in literature.

    • Performance analysis of variants of super-twisting sliding mode control based governor designs for hydraulic generating regulated system


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      Hydroenergy is considered as one of the largest contributors of electricity whose global consumption has been rising owing to the annual growth rate of world’s population. This necessitates the stable and safe operation of hydropower plants via robust control designs in hydraulic generating regulated system (HGRS). However, HGRS exhibits non-linear, chaotic and non-minimum phase characteristics and therefore, devising controller for such an intricate system is a difficult objective. Besides, the system is primarily constituted by several electrical, mechanical and hydraulic series with a hydro-generating module conjectured as a controlled system and speed governor as a controller. To this end, this paper enacts novel robust non-linear governor prototypes for the stabilization of chaotic HGRS using five kinds of super-twisting sliding modecontrol techniques (SSMCs) namely, fixed gain SSMC (FGSSMC), variable gain SSMC (VGSSMC), terminal SSMC (TSSMC), adaptive SSMC (ASSMC) and higher order SSMC (HOSSMC). In addition, all the devised techniques are substantiated via the renowned Lyapunov’s stability theorem. Furthermore, to test and analyze their tracking and robust performances, four case studies involving fixed point stabilization test, variable speed tracking, periodic orbit tracking and random varying speed tracking test despite random noises are also executed. Moreover, the efficacies and usefulness of the proposed methods are compared with the preliminary methods such as input- output feedback linearization SMC (IFSMC) and Optimal PID (Proportional Integral Derivative)control in terms of settling time, error performance indices, control energy and total variance in control signal.

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