Paul Puleston

Supervisor control for a stand-alone hybrid generation system using wind and photovoltaic energy

A comprehensive supervisor control for a hybrid system that comprises wind and photovoltaic generation subsystems, a battery bank, and an ac load is developed in this paper. The objectives of the supervisor control are, primarily, to satisfy the load power demand and, second, to maintain the state of charge of the battery bank to prevent blackout and to extend the life of the batteries. For these purposes, the supervisor controller determines online the operation mode of both generation subsystems, switching from power regulation to maximum power conversion. Decision criteria for the supervisor based on measurable system variables are presented. Finally, the performance of the supervisor controller is extensively assessed through computer simulation using a comprehensive nonlinear model of the plant.

Variable Structure Control of a Wind Energy Conversion System Based on a Brushless Doubly Fed Reluctance Generator

This paper introduces a variable structure robust controller for wind energy conversion systems based on brushless doubly fed reluctance machine. Two simultaneous control goals are tackled: maximization of the wind energy conversion efficiency and minimization of the machine copper losses. The proposed multiple-input multiple-output (MIMO) robust controller is systematically synthesized following a general design method for MIMO nonlinear affine systems. The design is approached through a theoretical framework based on the combination of variable structure techniques and the Lyapunovs theory. Robustness to bounded disturbances and chattering minimization is attained.

Control-Oriented Modeling and Experimental Validation of a PEMFC Generation System

An experimentally validated control-oriented model that reproduces the most typical features of a laboratory proton exchange membrane fuel cell generation system, is presented in this paper. The proposed representation is a 7th order fully analytical nonlinear model of ordinary differential equations, primarily focused on the system gases dynamics. The complete model is developed following a modular procedure, combining theoretical modeling techniques and empirical analysis based on experimental data. The presented methods can be used as a general modeling guideline for control-oriented purposes, being possible to adapt to other fuel-cell-based systems with similar characteristics.

Development and Implementation of a Supervisor Strategy and Sliding Mode Control Setup for Fuel-Cell-Based Hybrid Generation Systems

This paper presents the development and experimental results of a supervisor strategy and a sliding mode control setup to improve the performance of hybrid generation systems. The topology in this study is conformed by a core comprising a fuel cell module and a supercapacitor module, in combination with an alternative energy source module and an electrolyzer. In particular, a wind power turbine is considered as alternative power source to attain a hybrid generation system fully relying on renewable energy. First, a supervisor strategy is proposed to manage the power flows of the subsystems and coordinate the system as a whole. Subsequently, a sliding mode control setup for combined operation of the dc/dc power converters of the fuel cell/supercapacitor core is presented to track the power references synthesized by the supervisor control. Both control levels, supervisor strategy and sliding mode controllers, are implemented and assessed through extensive experimental tests under different wind conditions and heavy-load changes.

Variable gains super-twisting control for wind energy conversion optimization

An adaptive second order sliding mode control strategy is explored in this work, to maximize the energy extracted from the wind in a wind energy conversion system (WECS). It is required to such strategy to deal with the nonlinear nature of the WECS, the randomness of the wind speed, model uncertainties and external disturbances, and also with the need to reduce mechanical loads. The special features of this adaptive technique together with the robustness, relative simplicity and other desirable inherent characteristics of the super-twisting algorithm make the proposed controller an attractive solution. The suitability of the proposed strategy is proved by extensive computer aided simulations employing a comprehensive model of the system.

Fundamentals of Sliding-Mode Control Design

This chapter provides an introduction to Variable Structure Control theory and its extension to the so-called Sliding-Mode (SM) control. The presentation is not intended as a comprehensive survey of the state-of-the-art in the field, but to supply the basic concepts on SM control required to understand the developments to come in this book. The readers can use this material as a straightforward introduction to the field of SM control.

A Geometric Approach for the Design of MIMO Sliding Controllers. Application to a Wind Driven Double Output Induction Generator

This paper presents a systematic methodology to design controllers for a general class of nonlinear MIMO systems affine in the control in the presence of bounded uncertainties and disturbances. The proposed design method is developed through a theoretical framework based on the combination of a geometric approach and sliding mode techniques. The resulting robust control law guarantees finite time convergence, while chattering reduction is attained by utilising the minimum discontinuous action required to ensure disturbance rejection. The proposed methodology is applied to the control of a grid connected wind energy generation system based on a double output induction generator

Time-based adaptive second order sliding mode controller for wind energy conversion optimization

In this paper a novel time-based adaptive second-order sliding mode (SOSM) technique to optimise the efficiency of a variable-speed wind turbine is developed and analised. A revisited form of a recent time-based adaptation algorithm is proposed to deal with the characteristics and control requirements of the wind energy conversion system (WECS), particularly fastly varying disturbances due to gusty wind effects. The revisited algorithm, which enhances the reactivity of the adaptation strategy against fastly varying uncertainties, represents the main theoretical novelty of this work. The proposed controller is extensively assessed through computer simulation of the WECS under study.

Feasibility study of variable gain Super-Twisting control in fuel cells based systems

This work presents a controller based on a Super-Twisting (ST) algorithm with variable gains, designed to maximize the efficiency of a fuel cell (FC). The strategy consists on regulating the oxygen excess ratio, maintaining it at an optimum value in spite of external disturbances and model uncertainties. The tested algorithm has the well-known advantages of the original ST with fixed gains, such as simplicity, robustness against uncertainty and disturbances, reduced chattering and finite time convergence. In addition, the variability of its gains allows expanding the range of operation, without a significant increase in the complexity of the control law. The adjustment of the gains is based on certain variable bounding functions, which have to be determined analysing the system and its characteristics. This process is laborious for a non-linear system like the FC, but is performed off-line during the design stage. Promising results have been obtained through exhausting simulation tests, considering model uncertainties and highly variable load regimes.

PEM Fuel Cell Systems

Proton Exchange Membrane (PEM) fuel cells are extensively used for mobile and portable applications. This is due to their compactness, low weight, high power density, and clean, pollutant-free operation. Besides, their low temperature of operation (typically 60–80 degrees Celsius) allows fast starting times, a key feature for automotive applications, for instance. In a PEM Fuel Cell, a hydrogen-rich fuel is injected by the anode, and an oxidant (usually pure oxygen or air) is fed through the cathode. Both electrodes are separated by a solid electrolyte that allows ionic conduction and avoids electrons circulation. The output of a PEM Fuel Cell is electric energy, with water and heat as the only by-products. In this chapter, the basics of PEM fuel cells operation are reviewed, including electrochemical equations, losses, and efficiency issues. The state-of-the-art in PEM fuel cells technology is summarised, including membranes, electrodes, catalysts, line heaters, water, and heat management devices. Control-oriented models in the literature are discussed, and typical control objectives are analysed.