A novel speed optimisation scheme for unmanned sailboats by sliding mode extremum seeking control without steady-state oscillation

This paper proposes a novel speed optimisation scheme for unmanned sailboats by sliding mode extremum seeking control (SMESC) without steady-state oscillation. In the sailing speed optimisation scheme, an initial sail angle of attack is first computed by a piecewise constant function in the feed forward block, which ensures a small deviation between sailing speed and the maximum speed. Second, the sailing speed approaches to maximum gradually by extremum search control (ESC) in the feedback block. In SMESC without steady-state oscillation, a switching law is designed to carry out the control transformation, so that the speed optimisation system carries out SMESC in the first convergence phase and ESC without steady-state oscillation in the second stability phase. This scheme combines the advantages of both control algorithms to maintain a faster convergence rate and to eliminate steady-state oscillation. Furthermore, the strict stability of the speed optimisation system is proved in this paper. Finally, we test a 12-m mathematical model of an unmanned sailboat in the simulation to demonstrate the effectiveness and robustness of this speed optimisation scheme.

EXTREMUM SEEKING CONTROL OF TWO-STAGE ANAEROBIC DIGESTION SYSTEM: A MINI REVIEW

Anaerobic digestion (AD) is a biotechnological process, in which microorganisms degrade organic matter under anaerobic conditions to produce biogas. It has long been known that the two main species (acidogenic and methanogenic) in the community of microorganisms in AD differ in many aspects and the optimal conditions for their growth and development are different. Therefore, in AD in a single bioreactor (BR) (single-phase process), the optimal conditions are selected taking into account the slow-growing methanogens at the expense of fast-growing acidogens, which affects the efficiency of the whole process. This has led in recent years to the development of two-stage AD (TSAD), in which processes are divided into a cascade of two separate BRs. It is known that this division of the processes into two consecutive BRs leads to significantly higher energy yields for the two-phase system (H2 + CH4), compared to the traditional single-stage CH4 production process. In our previous studies different mathematical models of the TSAD have been developed. It was shown that in both BRs the input-output characteristics have a clear maximum, which allows the yields to increase significantly if operations are provided around the maximum points. However, in order to maintain the sustainability of the biogas plants work, it is necessary to introduce automatic control with sophisticated extremum seeking control (ESC) algorithms. This paper presents the pioneering research on ESC of AD process with production of hydrogen and methane. This research has been realized by the Department of Biotechnology at The Stephan Angeloff Institute of Microbiology (SAIM) and the French-Chinese Laboratory on Automatic Control and Signal Processing (LaFCAS), in collaboration with the Laboratory of Signals and Systems (L2S) at the French National Center of Scientific Research CNRS.

Using Extremum Seeking Control to Improve the Power Capture of Midsize Hydrostatic Wind Turbines

Adaptive control strategies are commonly used for systems that change over time, such as wind turbines. Extremum Seeking Control (ESC) is a model-free real-time adaptive control strategy commonly used in conventional gearbox wind turbines for Maximum Power Point Tracking (MPPT). ESC optimizes the rotor power by constantly tuning the torque control gain (k) when operating below rated power. The same concept can be applied for hydrostatic wind turbines. This paper studies the use of ESC for a 60-kW hydrostatic wind turbine. First, a systematic approach to establish the ideal ESC is shown. Second, a comparison of the power capture performance of ESC versus the conventional torque control law (the kω2 law) is shown. The simulations include a timesharing power capture coefficient (Cp) to clearly show the advantages of using ESC. Studies under steady and realistic wind conditions show the main advantages of using ESC for a hydrostatic wind turbine.