A strategy to regulate unstable processes using a modified Smith predictor based sliding mode controller (SP-SMC) is illustrated. The proposed scheme presents disturbance rejection and optimal control input usage with overall improved regulatory performances. The unstable process with time delay is first estimated using a simple measurement of limit cycle output obtained from a modified relay experiment. Then this paper extends a work on SP-SMC for unstable processes, which leads to significant improvements in its regulatory capacities of reference inputs and disturbances. A new control law is incorporated in the discontinuous part of sliding mode control such that the overall performance improves significantly. The metaheuristic search algorithm with some modifications has been implemented successfully to satisfy the new control performance index. The robustness of the controller is also tested under the process uncertainty. Illustrative examples show the simplicity and superiority of the presented design method over previously published approaches.
Supercapacitors have been rapidly adopted to replace batteries in many instances from power tools to automotive and aviation. Designing systems incorporating supercapacitors necessitate an accurate model of supercapacitor to maintain system efficiency. However, due to varying impedance property of supercapacitor, modeling becomes critical with likelihood of introducing errors. This work proposes an enhanced model to predict the system dynamics under various initial state of charge in supercapacitors. The proposed flexible model is suitable to represent actual supercapacitor impedance without prior assumption on the model structure. The use of one model to cover the other various impedance structures is simple and possible to estimate accurate supercapacitor's impedance. Selection of impedance structure is selfregulated to improve the accuracy with minimum variables. To illustrate the variable structure fractional model, experimental results are shown with three different values of supercapacitors from three different manufacturers.
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