Fotis Stergiopoulos

Robust constrained stabilization of a boost DC-DC converter with Lyapunov-based control and piecewise-linear Lyapunov functions

In this paper we describe a new methodology for designing robust and efficient state-feedback control laws for a switched-mode boost DC-DC power converter. The proposed design is adopting the so-called Lyapunov-based control law and attempts to solve the robust constrained stabilization problem under large parameter variations. With the methodology proposed static or switching state-feedback control laws are generated so that a number of further key issues are addressed, i.e. low complexity of the implementation, accurate nonlinear dynamics incorporation, nonconservative handling of hard state and control constraints, robustness to supply voltage variations, set-point and load changes. The control design procedure is based on the generation of controlled invariant polytopes (safety domains) using piecewise-linear Lyapunov functions. The proposed technique is numerically evaluated using the exact switched model of the converter.

Energy management in a stand-alone power system for the production of electrical energy with long term hydrogen storage

This paper deals with the importance of an efficient energy (or power) management strategy (EMS) on an existing stand-alone power system that uses renewable energy sources for the production of electrical energy. Due to the intermittent nature of the renewables, part of this energy is used to split the water for the production of hydrogen, which is stored and used later for the production of energy in a PEM fuel cell, in case of high energy demands. The energy management algorithms aim at the reliable and effective control of the energy flow that is basically used to meet the load requirements of the autonomous system. The developed simulated algorithms were compared to each other in order to determine the most efficient strategy as far as hydrogen production and autonomy are of concern. Parametric sensitivity was also a major issue which was studied extensively. All the results and outcomes of such an analysis are considered as the basis for the optimization and control study of similar stand-alone power systems.

Optimal switching Lyapunov-based control of a boost DC-DC converter

A new methodology for designing robust and efficient state-feedback control laws for a switched-mode boost DC-DC power converter has been recently proposed. This approach has adopted the so-called stabilizing or Lyapunov-based control paradigm which is well-known in the area of energy-based control of DC-DC converters, whereby the control law takes a state-feedback form parameterized by a positive scalar γ. Extension to state-dependent switching state-feedback control laws has been proposed, where the switching surfaces are parameterized by a number of positive scalars γ.i. In this paper this methodology is revisited by considering the problem of designing optimal switching state-feedback control laws, i.e. finding the optimal control parameters γ.i corresponding to the optimal position of the switching surfaces. This permits minimization of the number of switchings required for achieving an optimal performance and hence reduced complexity of the control law. Systematic derivation of gradient information to apply gradient-descent algorithms is provided. The proposed technique is numerically evaluated using the exact switched model of the converter.

Optimal switching Lyapunov-based control of power electronic converters

This paper presents new ideas and insights towards a novel optimal control approach for power electronic converters. The so-called stabilizing or Lyapunov-based control paradigm is adopted, which is well known in the area of energy-based control of power electronic converters, in which the control law takes a nonlinear state-feedback form parameterized by a positive scalar λ. The first contribution is the extension to an optimal Lyapunov-based control paradigm involving the specification of the optimal value for the parameter λ in a typical optimal control setting. The second contribution is the extension to more flexible optimal switching-gain control laws, where the optimal switching surfaces are parameterized by a number of positive scalars λj. Systematic derivation of gradient information to apply gradient-descent algorithms is provided. The proposed techniques are numerically evaluated using the exact switched model of a DC-DC boost converter. Copyright

Study of an integrated system for the production of hydrogen by autothermal reforming of methanol

Abstract In this study a mathematical model is developed and evaluated in order to describe an experimental methanol fuel processor (a combination of autothermal reformer and preferential oxidation reactor) for the production of hydrogen to be used it as the main fuel of a Proton Exchange Membrane Fuel Cell (PEMFC) for the generation of 1kW electrical power. This integrated system has been studied from a theoretical and an experimental point of view where different parameters were studied in order to maximize hydrogen production and keep in a low content carbon monoxide. The main variables that are of concern in this study, are the temperature and the concentrations of the reactants and products as a function of the length of the reactors. By utilizing kinetic expressions developed for this catalytic system, the results of the simulations are found in good agreement with the results obtained from the experimental implementation.

State-feedback control of an interleaved DC-DC boost converter

This paper extends a recently proposed statefeedback control design method from a simple DC-DC boost converter to a multi-phase interleaved DC-DC boost converter with an arbitrary number of legs. Both static and dynamic state-feedback pole placement control laws are considered. In the case of static state-feedback control a bifurcation analysis procedure that can predict the generation of multiple equilibria is introduced. This analysis can be integrated into the control design so that multiple equilibria can be completely avoided or ruled out of the operating region of interest. The proposed control laws are digitally implemented and verified in a 2-leg case study using both simulation and real experimentation.

Behaviour Assessment of a Fuel Cell - Battery System Using a Supervisory Control Methodology Empowered by a Hybrid Timed Automaton (HTA)

Abstract This work presents the design and development of a supervisory control methodology for the management of energy decisions in a hybrid powered system. More specifically the methodology implements an energy management strategy (EMS) which is applied in a fuel cell – battery system for vehicular applications and explores the behaviour of the system under a realistic operation scenario. The EMS relies on a Hybrid Timed Automaton (HTA) combined with propositional rules and formalizes the operation of the system as it thoroughly describes the dynamic transitions between each operating state. A sensitivity analysis reveals the influence of the power distribution between the two energy sources and an optimization study determines the values of the selected operating parameters. Finally the response of the Fuel Cell Electric Vehicle (FCEV) system is assessed through a combined urban and high-way driving cycle.

Flexible polyhedral Lyapunov functions for the robust constrained stabilization of bilinear boost DC-DC converters

Recent research efforts, relying on constrained stabilization principles, have been concentrated on the design of robust and efficient state-feedback control laws for switched-mode DC-DC boost converters, characterized by accurate nonlinear dynamics incorporation, nonconservative handling of hard state and control constraints, and robustness to supply voltage variations and load changes. This paper focuses on the efficient construction of flexible polyhedral Lyapunov functions, which can facilitate control design procedures which address all aforementioned issues via the generation of contractive polytopes (safety domains). New non-conservative conditions for the averaged-model bilinear converter dynamics and a corresponding ray-gridding algorithm are proposed that allow near-maximal approximations of the real stability domains with negligible computational cost. A significant improvement in the size of the contractive domains is obtained by resorting to more flexible partial contractivity conditions. This novelty allows the extension of the constrained stabilization framework to robust constrained tracking, whereby a wide operating region may be covered. The proposed ideas can be applied for the specification of affine state-feedback control laws and are numerically evaluated on a boost converter example using the exact switched model of the converter.

Application of Neural Networks Solar Radiation Prediction for Hybrid Renewable Energy Systems

In this paper a Recurrent Neural Network (RNN) for solar radiation prediction is proposed for the enhancement of the Power Management Strategies (PMSs) of Hybrid Renewable Energy Systems (HYRES). The presented RNN can offer both daily and hourly prediction concerning solar irradiation forecasting. As a result, the proposed model can be used to predict the Photovoltaic Systems output of the HYRES and provide valuable feedback for PMSs of the understudy autonomous system. To do so a flexible network based design of the HYRES is used and, moreover, applied to a specific system located on Olvio, near Xanthi, Greece, as part of SYSTEMS SUNLIGHT S.A. facilities. As a result, the RNN after training with meteorological data of the aforementioned area is applied to the specific HYRES and successfully manages to enhance and optimize its PMS based on the provided solar radiation prediction.

Evaluation of Design Issues and Automation Infrastructure in a Solar-Hydrogen Production Unit at CERTH in Thessaloniki

Abstract Objective of the presented study is to evaluate the technical and design issues required prior to the full operation of a solar-hydrogen integrated system. The required measurements, sensors and control elements are a prerequisite for a flexible automation structure and finalization of the process flowsheet. The control strategy and system monitoring are realized on an industrial Supervisory Control and Data Acquisition (SCADA) system. The control strategy is further independently developed based on the system mathematical model and according to the theory of Hierarchical Control. Its evaluation is performed through an one-year simulation study for the conditions of region of installation where the effect of the main system variable on the overall operation is reported.