Academic Writing: Introduction and conclusion

An effective introduction explains the purpose and scope of the paper to the reader. The conclusion should provide a clear answer to any question asked in the title, as well as summarizing the main points.

A common framework in an introduction

In an introduction much depends on the type of research a person is conducting, but a common framework is:

a. Definition of key terms, if needed.

b. Relevant background information.

c. Review of work by other writers on the topic.

d. Purpose or aim of the paper.

e. Your methods and the results you found.

f. Any limitations you imposed.

g The organization of your work.

Read this introduction sample, then highlight the components of a common framework in an introduction:

Introduction

Modern electric (electromagnetic) generators and motors have started with the “Law of electromagnetic induction” attributed to Faraday (1831), but recently found by us formulated as an experimental fact in Lucretius book: “The Nature of Universe” 1st century B.C., in Rome, in terms of repelling and attraction electromagnetic forces of a moving magnet on a copper cap above it. After Faraday’s homopolar and heteropolar DC brush machines, induction AC cage – rotor (brushless) machines have been introduced, with paramount contributions by Siemens brothers, Galileo Ferraris and Nikola Tesla.

The patents of first induction motors (Fig. 1a,b) showed great promise – as travelling field brushless AC machines – but their topologies were rather primitive and thus efficiency was low. Soon after that, before 1900, the windings have been put in slots (as of today) by Dolivo Dobrovolski and others, to produce practical performance.

Even before 1900 DC excited–rotor AC (synchronous) generators have been introduced, even with additional PMs on the rotor and with today’s popular tooth-wound stator a.c. windings as in an AEG 1896 patent (with 36 slots and 42 rotor poles).

Based on these “building bricks”, DC and then AC power grids have been developed, first local, then regional, national and continental from 1900 to 1960. Power grids rely on paralleling AC synchronous generators (whose power per unit increased to 1800 MW for turbo generators and 770 MW recently for hydrogenerators on Yantze River) controlled with a small droop in frequency (less than 0.5 Hz) and in voltage (a few %) control to allow input power sharing from different generators based on energy availability, demand, reliability and cost.

Electric installed power and electric energy grew steadily over the last century with a particular surge in the last 20 years due to the emergent economies in large population areas (in Asia, Africa, S. America). But so did the environmental concerns. This is how “renewable energy” emerged at the forefront (Fig. 2 a, b).

Renewable energy sources (hydro, wind, waves, solar – thermal) do not bring more energy (heat) on earth, while fossil fuel sources do; they also do less harm to the environment. But they are characterized by load power density (nuclear power turbine + generator weights 50 times less than a wind turbine – generator per kW). Consequently, the need for better harnessing renewable energy turbine–generator systems is imperative. On the other end, saving electric energy by its more intelligent usage, to do “mechanical useful work by electric motors”, has led to variable speed motor drives (Fig. 3a,b).

The advantage of variable speed in electric generators has been capitalized mainly in the last 10 years in wind generator systems with AC–DC–AC power electronic interfaces. It was soon realized that, even for limited variable speed range (and power electronics fractional p.u. ratings), besides increased efficiency, the flexibility gains in electric power faster control are even more important. The first breakthrough was represented by 400 MVA pump–storage hydroplants with variable speed wound–rotor induction generators (DFIGs), introduced in Japan, in 1994. Recently 230 MVA such variable speed DFIG system was introduced to pump storage hydro-plants in Europe.

But the renewable distributed energy resources led to massive introduction of power electronics (and variable speed) in distributed (intelligent) power grids. In view of the wide spectrum of electric generator and motor systems and the rich heritage of books, articles and patents on them (see for selected references) in what follows we will concentrate on recent progress and future trends in a few representative applications:

• Electric generators in high power systems, Section2

• Renewable energy variable speed generators in distributed power systems, Section 3

• Autonomous electric generators in transport and industry, Section 4

• Industrial electric drives, Section 5

• Electric propulsion systems, Section 6

• Electric drives in residential applications, Section 7

• Electric actuators in info-gadgets, Section 8

• Line start higher efficiency motors, Section 9

Note. Another valid approach would have been, perhaps, to treat recent progress and future trends by looking into: principles, topologies for various speed and power ranges, multi-physics modeling and optimal design methodologies, control methods by power electronics, testing, commissioning, monitoring, maintenance, while mentioning, in passing, selected applications. As most potential readers are rather familiar academically with the subject, we selected here the more practical criterion of applications which is not without shortcomings, either.

Parts of conclusion:

·       summary of the main points of the essay

·       no new arguments or important information

·       the arguments (made in the body of the essay) can be logically extended by making recommendation or prediction

·       it’s not a novel; there are no surprising endings

·       the best thing is if the conclusion can be tied back to introduction (hard to write)

·       summary of the main points of the essay

·       no new arguments or important information

·       the arguments (made in the body of the essay) can be logically extended by making recommendation or prediction

·       it’s not a novel; there are no surprising endings

·       the best thing is if the conclusion can be tied back to introduction

 

Read this conclusion sample, then highlight the parts of conclusion:

Conclusion

Electric (electromagnetic) machines (EMs) started with Faraday’s law of “electromagnetic induction” (1831) found, spelled as an experiment with attraction and repulsive (induced currents) forces, in Lucretius “The nature of Universe”, book, the year 60 B.C.

EMs convert mechanical energy to electric energy (generator mode) or vice – versa (motor made) via stored magnetic energy. Energy balance is crucial in analyzing EMs.

EMs may develop (experience) rotary or linear or hybrid motion.

Standard EMs developed already by 1900 classify into DC (AC) brush (fixed field) machines and AC (traveling field) machines: asynchronous/induction and synchronous.

Electric energy is obtained through electric generators (except for photovoltaic energy) with powers/unit up to 1800 MVA (turbgenerators driven by fossil or nuclear fuel turbines) and up to 770 MVA in hydrogenerators (recently on Iantze River)

More than 60% of electric energy is producing “mechanical useful work” in electric motors, which may be line – started (fix speed) or fed from PWM static power converters (for variable speed).

The last 50 years witnessed staggering progress in:

·       Lighter and more efficient large power generators

·       Optimal multi-physics design methodologies using magnetic equivalent circuit (MEC) and FEA

·       The extension of PM usage in variable speed synchronous machine drives (with PWM AC-DC-AC static converter interfaces); from subwatt to a few MW power (3 MWA, 15 rpm PMSGs for wind energy conversion)

·       As the offer of quality (high energy) magnets is limited, it is anticipated that PMs will be used only when the cost is not the first target, but weight and efficiency are (low PM weight/kW), when high speed applications are favored

·       Combining lower cost magnets on rotor and on stator with single and (or) double magnetic saliency in “brushless” motors has led to an avalanche of “novel” topologies, augmented by tooth-wound stator windings in the last 20 years; some are close to worldwide market entrance.

The present paper presents a summary of the recent progress in EMs, rotary and linear (MAGLEVs, included) following eight important application domains, with key literature citations, and infer some avenues for further developments.

The paper is by no way complete or fully objective and inevitably reflects both the horizon and the limits of the author. Consequently, criticism is welcome.