Intelligent Control of the Energy Generation Systems

Intelligent Control of the Energy Generation Systems

Nicu Bizon (University of Pitesti, Romania)
DOI: 10.4018/978-1-60566-737-9.ch002
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Abstract

In this book chapter are analyzed the Energy Generation System (EGS) topologies, used in automotive systems, and the grid inverter systems, with intelligent control algorithms (fuzzy logic controller, genetic algorithm, etc.). The EGS blocks are modelled using Matlab & Simulink ® program. A necessary block is the EGS power interface between the fuel cell stack and the batteries stack, usually a boost converter that uses a Peak Current Controller (PCC) with a Boundary Control with Current Taper (BCCT). The control law is a function of fuel cell current and battery voltage, which prevents the “boiling” of the batteries. The control objective for this power interface is also the fuel cell current ripple minimization, used in order to improve the fuel cell stack life cycle. Clocked and non-clocked control methods are tested in order to obtain a small fuel cell current ripple, better a dynamic response, and robustness against system uncertainty disturbances. The EGS behaviour is tested by bifurcation diagrams. It is shown that performances increase if the control law is a function that depends by the fuel cell current ripple and battery voltage. The clocked PCC using the BCCT 2-D law is implemented by a fuzzy logic controller. The power load dynamic is compensated using an ultracapacitors stack as a dynamic energy compensator, connected by a bi-directional converter to the batteries stack bus. Small fuel cell current ripple using compact batteries and ultracapacitors stacks will be obtained by the appropriate design of the control surface, using an Integrated Fuzzy Control (IFC) for both power interfaces.
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Introduction

Power electronics is an interdisciplinary “green” technology (electronics, electrical engineering, automatic control and, obviously, mathematics and physics), with three main aims:

  • To convert electrical energy from one of the other energy forms, facilitating its regulation and control (main objective of this chapter);

  • To achieve high conversion efficiency;

  • To minimize the mass of power converters.

The specific objective of this book chapter will be to promote new control techniques for Energy Generation System (EGS) based on intelligent concepts. The typical Energy Generation System topology with Energy Storage Device (ESD) is presented in figure 1. The energy storage technologies, usually used in an EGS, are such as presented below.

Figure 1.

A typical energy generation system topology with energy storage devices

Electrochemical Energy Storage

Batteries

The lead-acid battery has a high specific energy as compared to other energy storage technologies, but the specific power is lower due to the high internal impedance (contact resistance between the electrodes and the electrolyte). Researches into this battery type are mainly focused on its construction, so that, after more than 150 years, the chemical reactions remain the same. Efforts to increase the power delivery capabilities of lead-acid batteries are reported in:

  • Thin Metal Film (TMF) battery by Bolder Technologies Corporation (USA). The 2V/1,5Ah Bolder TMF cell can be fully discharged in 1s at over 1kA, and then fully recharged in a few minutes. It has a specific power, of about 5kW/kg, and could now reach over 15kW/kg.

  • The bipolar lead-acid battery. It achieves a specific power of up to 1kW/kg, and a power density of 35 MW/m3. For reasons of price, this kind of battery is usually used in an EGS.

  • High power Li-ion. These batteries achieve over 1kW/kg specific power, at a higher specific energy than the bipolar lead-acid battery, but lower than the Bolder TMF batteries.

    • To conclude, these technologies have high-energy storage capabilities, with a lesser performance in power delivery. As far as the charge/discharge time constants are concerned, the batteries belong to the time transfer range of one minute up to several hundreds of hours, which makes them long-term energy storage devices.

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