Additional Insights into Power Electronics

There are several striking features of power electronics, the foremost among them being the extensive use of inductors and capacitors. In many applications of power electronics, an inductor may carry a high current at a high frequency. The implications of operating an inductor in this manner are quite a few, such as necessitating the use of litz wire in place of single-stranded or multi-stranded copper wire at frequencies above 50 kHz, using a proper core to limit the losses in the core, and shielding the inductor properly so that the fringing that occurs at the air-gaps in the magnetic path does not lead to electromagnetic interference. Usually the capacitors used in a power electronic application are also stressed. It is typical for a capacitor to be operated I a high frequency with current surges passing through it periodically. This means that the curent rating of the capacitor at the operating frequency should be checked its use. In addition, it may be preferable if the capacitor has self-healing property. Hence an inductor or a capacitor has to be selected or designed with care, taking into account the operating conditions, before its use in a power electronic circuit. In many power electronic circuits, diodes play a crucial role. A normal power diode is usually designed to be operated at 400 Hz or less. Many of the inverter and switch-mode power supply circuits operate at a much higher frequency and these circuits need diodes that turn ON and OFF fast. In addition, it is also desired that the turning-off process of a diode should not create undesirable electrical transients in the circuit. Since there are several types of diodes available, selection of a proper diode is very important for reliable operation of a circuit. Analysis of power electronic circuits tends to be quite complicated, because these circuits rarely operate in steady-state. Traditionally steady-state response refers to the state of a circuit characterized by either a dc response or a sinusoidal response. Most of the power electronic circuits have a periodic response but this response is not usually sinusoidal. Typically, the repetitive or the periodic response contains both a steady-state part due to the forcing function and a transient part due to the poles of the network. Since the responses are nonsinusoidal, harmonic analysis is often necessary. In order to obtain the time response, it may be necessary to resort to the use of a computer program.

WORD LIST:

Power electronics -силовая электроника; электроника

больших мощностей

power semiconductor device -силовой полупроводниковый

прибор,(однооперационный) тиристор

silicon-controlled rectifier (SCR) - кремневый силовой полупроводниковый прибор (однооперационный) триодный тиристор

mercury-arc rectifier -ртутный выпрямитель

drive - приводное устройство

Inverter - преобразователь

Conversion - преобразование

chopper - преобразователь прерыватель; инвертор

cycloconverter - понижающий преобразователь

cycloinverter -повышающий преобразователь частоты

rectification - выпрямление (тока) частоты,

statific switch -бесконтактный переключатель,

- статический коммутатор

fully-controlled rectifier -полностью управляемый

- выпрямитель (автомат)

bridge -электрический шунт;

-параллельное присоединение

inter-phase transformer (IPT) -межфазный трансформатор

bipolar junction transistor(BJT) -биполярный (плоскостной) транзистор

Metal Oxide Semiconductor

Effect Transistor (MOSFET) - полевой МОП - транзистор

insulated gate bipolar -биполярный транзистор

transistors (IGBT) - с изолированным затвором

MOS-controlled thyristor (MCT) -МОП - управляемый тиристор

gate turn-off thyristor (GTO) -запираемый теристор

uninterrupted power supply - источник бесперебойного питания

step-down switch-mode - понижающий переключающийся

power supply источник(питания)

step-up chopper - повышающий (пошаговый) преобразователь

fly-back converter - преобразователь обратного хода

resonant converter - резонансный преобразователь

traction motor - тяговый электродвигатель

mains - магистральная электролиния,

линия сильных токов

triac - триодный тиристор; триак, симистор

inductor - индукционная катушка, дроссель

capacitor - конденсатор

litz wirе - многожильный провод

(обмоточный, высокочастотный)

single-stranded - одножильный провод

wire multi-stranded copper wire - многожильный медный провод,

кабель

fringing - растрепывание, нарушение (изоляции)

current rating - режим (номинал) по току

current surge - выброс тока

elf-healing property - самовосстанавливающиеся характеристики

electrical transient - электрический импульс (мгновенный)

steady state response - характеристика устойчивого режима

EXERSICES:

I. Answer the following questions:

a) What is power electronics designed for?

b) Name main forms of electrical power conversion

c) Explain the principle diffidence between rectifier and inverter*.

d) Does input voltage of a cycloconverter have fixed amplitude and freq|

e) What is the typical application of a cycloconverter?

f) Tгу to explain the difference between litz wire and single-stranded they conductors?

g) What is the task done by a diode in the electrical circuits?

II. Translate into English words in brackets and then the sentences into Russian:

a) Advent of silicon-controlled rectifiers, led to the development of a new area of application called the (силовая электроника)

b) For low voltage, high current applications, a pair of (трёхфазный), three-pulse rectifiers interconnected by an (межфазовый трансформатор)

c) There are several types of diodes available, selection of а (нужный, (ветствующий диод) is very important for reliable operation of a circuit. Traditionally (устойчивые, постоянные характеристики) refers to the state of a circuit characterized by either a dc response or a sinusoidal response.

d) Many of the inverter and switch-mode power supply circuits operate at a much выcокая частота) and these circuits need diodes that (включать и выключать) fast. Before the application the (номинал по току) of the capacitor at the (рабочая в should be checked before its use.

e)A typical application of а (повышающий преобразователь частоты) is to use it for rolling the speed of an ас (тяговый двигатель).

III. Transtlate the following text:

Conductors

Conductors are materials having a low resistance, so that current easily passes though them . The lower the resistance of the material, the more current can pass through it. Most solid materials are classified as insulators because they offer very large resistance to the flow of electric current. Metals are classified as conductors because electrons are not tightly bound, but in most materials even the outermost are so tightly bound that there is essentially zero electron flow through them with ordinary voltages. And silver and copper are the best conductors. The advantage of copper is that it is much cheaper than silver. Thus, copper is widely used to produce conductors. One of the common functions of wire conductors is power supply to a load, for example a traction motor. Since copper wire conductors have a very low resistance they produce a min voltage drop while electrical current passes.

The conductor implies that the outer electrons of the atoms are loosely bound and free to move through the material. Most atoms hold on to their electrons tightly and are insulators. In copper, the valence electrons are essentially free and strongly repel each other. Any external influence which moves one of them will cause a repulsion of other electrons which propagates, "domino fashion" through the conductor.

Most materials change the value of resistance when their temperature varies

IV. Translate the following sentences:

Сила электрического тока в проводе определяется как электрический |заряд проходящий через поперечное сечение провода за единицу времени. Заряд измеряется в кулонах (coulombs), один кулон в секунду равен одному амперу.

b) Направлением тока считается направление, в котором двигаются положи­тельные заряды. На самом деле ток в большинстве случаев создается движением отрицательно заряженных электронов, и это движение может быть в любом на­правлении.

c) The term "semiconductor" means "half-conductor, that is, a material whose conductivity ranges between conductors and non-conductors or insulators. While the conductivity of metals is very little influenced by temperature, conductivity of semi­conductors sharply increases with heating and falls with cooling. This dependence has

opened great prospects for employing semiconductors in measuring techniques.

d) Если для перемещения заряда между двумя точками необходимо затра­тить энергию или если при перемещении заряда между двумя точками заряд при- обретает энергию, то говорят, что в этих точках имеется разность потенциалов.

Энергия необходима для перемещения заряда от более низкого потенциала к бо|лее высокому. На схемах рядом с точкой более высокого потенциала ставится +, а рядом с точкой более низкого - знак.

e) Батарея или генератор электрического тока — это устройство, которое со- общает энергию зарядам. Источник тока перемещает положительные заряды от меньшего потенциала к большему за счет химической энергии. Разность потенциалов на зажимах батареи или генератора называется электродвижущее (ЭДС). Разность потенциалов и ЭДС измеряются в вольтах.

f) Sunlight like heat can feed our electric circuit. Photocells made of semiconducting materials are capable of transforming ten per cent of sunray energy into electric power. Semiconducting materials are also excellent means of a constant maintaining a temperature irrespective of the surrounding temperature changes.

V. Translate into English:

Теория цепей

Цепь может представлять собой любую комбинацию батарей и генераторов а также резистивных и реактивных элементов. Батареи и генераторы в теории цепей рассматриваются либо как источники напряжения (ЭДС) с определенным внутренним сопротивлением, либо как источники тока с определенной внутренней проводимостью. Цепь, не содержащая источников тока и напряжения, называется пассивной, а цепь с источниками тока или напряжения - активной. Целью анализа цепи является определение полного сопротивления (импеданса) между любыми двумя точками цепи и нахождение математического выражения для тока через любой элемент цепи или для напряжения на любом элементе цепи при любыхзаданных ЭДС источников напряжения и любых токах источников тока. Всякий

замкнутый путь тока в цепи называется контуром. Узлом цепи называется всякая ее точка, в которой соединяются три или большее число ветвей цепи.

VI. Translate into Russian:

Current supply

Pertain types of telecommunication equipment require an ACsupply. Even in such

Cases the main's ac is first converted into DC- because this cab be stored in a storage battery which gives a constant supply of current independent of the mains and possible troubles affecting them - and then converted back into AC.This last-mentioned conversion can be done by means of a motor-generator, i.e., a DCmotor driving an ACgenera­lly means of an inverter. Two motor-generators or two inverters are connected in parallel, in order to improve operational reliability. For telecommunication installations are in remote location with no on-the-spot attendant personnel - e.g., directional Kansmitters-it may be advantageous to connect the power supply directly with a standby supply system. The requisite electrical power for operating the equipment is obtained from a generator whose shaft is coupled to that of an electrical motor (with flywheel) which in turn is connected, through an induction coupling, to a diesel engine.

Under normal operating conditions the motor, supplied with current from the mains, drives the generator and the flywheel. In the event of a power failure in the main, the induction coupling engages, and the momentum of the flywheel provides sufficient mechanical power to start the diesel engine. The latter runs at the same speed as the motor, which has now been automatically disconnected from the main. When the main supply pestered, the diesel engine is mechanically disconnected and the motor is electrically reconnected to the main.

LESSON #2

HOW RADIO WORKS

Simple Transmitters

You can get an idea for how a radio transmitter works by starting with abattery and a piece of wire. You can see that a battery sends electricity (a stream of electrons) through a wire if you connect the wire between the two terminals of the battery. Themoving electrons create a magnetic field surrounding the wire, and that field is strongenough to affect a compass.

Let's say that you take another wire and place it parallel to the battery's wire but several inches (5 cm) away from it. If you connect a very sensitive voltmeter to the wire,then the following will happen: Every time you connect or disconnect the from the battery, you will sense a very small voltage and current in the second changing magnetic field can induce an electric field in a conductor — this is the basicprinciple behind any electrical generator. So:

The battery creates electron flow in the first wire.

The moving electrons create a magnetic field around the wire.

The magnetic field stretches out to the second wire.

Electrons begin to flow in the second wire whenever the magnetic field in the first wire changes.

One important thing to notice is that electrons flow in the second wire only when you connect or disconnect the battery. A magnetic field does not cause electrons to flow in a wire unless the magnetic field is changing. Connecting and disconnecting the bat­tery changes the magnetic field (connecting the battery to the wire creates the magnetic field, while disconnecting collapses the field), so electrons flow in the second wire at I two moments.

Receiving an AM Signal

Here's a real world example. When you tune your car's AM radio to a station — for exempal, 680 on the AM dial — the transmitter's sine wave is transmitting at 680,000 hertz (the sine wave repeats 680,000 times per second). The DJ's voice is modulated that carrier wave by varying the amplitude of the transmitter's sine wave. An ampliefier amplifies the signal to something like 50,000 watts for a large AM station. The antenna sends the radio waves out into space.

So how does your car's AM radio — a receiver—receive the 680,000-hertz signal that IS sent and extract the information (the DJ's voice) from it? Here are the steps:

· Unless you are sitting right beside the transmitter, your radio receiver needs an antenna to help it pick the transmitter's radio waves out of the air. An AM antenna is simply a wire or a metal stick that increases the amount of metal (he transmitter's waves can interact with.

· Your radio receiver needs a tuner. The antenna will receive thousands of sine waves. The job of a tuner is to separate one sine wave from the thousands of radio signals that the antenna receives. In this case, the tuner is tuned to receive the 680,000-hertz signal.

· Tuners work using a principle called resonance. That is, tuners resonate at, and amplify, one particular frequency and ignore all the other frequencies in the air. It is easy to create a resonator with a capacitor and an inductor.

· The tuner causes the radio to receive just one sine wave frequency (in this case, 680,000 hertz). Now the radio has to extract the DJ's voice out of that sine wave. This is done with a part of the radio called a detector or demodu­lator. In the case of an AM radio, the detector is made with an electronic component called a diode. A diode allows current to flow through in one direction but not the other, so it clips off one side of the wave, like this:

· The radio next amplifies the clipped signal and sends it to the speakers (or a headphone). The amplifier is made of one or mote transistors (more transisters means more amplification and therefore more power to the speakers).

· In an FM radio, the detector is different, but everything else is the same. In FM, the detector turns the changes in frequency into sound, but the antenna, tuner and amplifier are largely the same.

Transmitting Information

If you have a sine wave and a transmitter that is transmitting the sine wave into space with an antenna, you have a radio station. The only problem is that the sine wave doesn't contain any information. You need to modulate the wave in some way to encode information on it. There are three common ways to modulate a sine wave:

•Pulse Modulation — In PM, you simply turn the sine wave on and off. This is an easy way to send Morse code. PM is not that common, but one good example of it is the radio system that sends signals to radio-controlled clocks United States. One PM transmitter is able to cover the entire United States!

•Amplitude Modulation — Both AM radio stations and the picture part of a TV signal use amplitude modulation to encode information. In amplitude modulation, the amplitude of the sine wave (its peak-to-peak voltage) chang­es. So, for example, the sine wave produced by a person's voice is overlaid onto the transmitter's sine wave to vary its amplitude.

· Frequency Modulation — FM radio stations and hundreds of other wireless technologies (including the sound portion of a TV signal, cordless phones, cell phones, etc.) use frequency modulation. The advantage to FM is that it is largely immune to static. In FM, the transmitter's sine wave frequency changes very slightly based on the information signal.

Onсе you modulate a sine wave with information, you can transmit the information!

Antenna: Real-life Examples

Let’s say that you are trying to build a radio tower for radio station 680 AM. It is transmitting a sine wave with a frequency of 680,000 hertz. In one cycle of the sine the transmitter is going to move electrons in the antenna in one direction, switch and pull them back, switch and push them out and switch and move them back again. In other words, the electrons will change direction four times during one cycle of the since wave. If the transmitter is running at 680,000 hertz, that means that every cycle completes as in (1/680,000) 0.00000147 seconds. One quarter of that is 0.0000003675 seconds. At the speed of light, electrons can travel 0.0684 miles (0.11 km) in 0.0000003675seconds. That means the optimal antenna size for the transmitter at 680,000 hertz is

About 361 feet (110 meters). So AM radio stations need very tall towers. For a cell phone working at 900,000,000 (900 MHz), on the other hand, the optimum antenna size is about 8.3 cm or 3 inches. This is why cell phones can have such short antennas.

You might have noticed that the AM radio antenna in your car is not 300 feet long- it is only a couple of feet long. If you made the antenna longer it would receive better, but AM stations are so strong in cities that it doesn't really matter if your antenna e optimal length.

You might wonder why, when a radio transmitter transmits something, radio waves want to propagate through space away from the antenna at the speed of light. Why can radio waves travel millions of miles? Why doesn't the antenna just have a magnetic field around it, close to the antenna, as you see with a wire attached to a battery? One simple way to think about it is this: When current enters the antenna, it does create a magnetic field around the antenna. We have also seen that the magnetic field will create an elec­tric field (voltage and current) in another wire placed close to the transmitter. It turns out that, in space, the magnetic field created by the antenna induces an electric field in space. This electric field in rum induces another magnetic field in space, which induces another electric field, which induces another magnetic field, and so on. These electric and magnetic fields (electromagnetic fields) induce each other in space at the speed of light, traveling outward away from the antenna.

Bluetooth Basics

Bluetooth is a standard developed by a group of electronics manufacturers mat al­lows any sort of electronic equipment — from computers and cell phones to keyboards and headphones — to make its own connections, without wires, cables or any direct action from a user. Bluetooth is intended to be a standard that works at two levels:

It provides agreement at the physical level — Bluetooth is a radio-frequency standard.

It also provides agreement at the next level up, where products have to agree on

when bits are sent, how many will be sent at a time and how the parties in a conversation can be sure that the message received is the same as the message sent.

The companies belonging to the Bluetooth Special interest Group, and more than 1,000 of them, want to let Bluetooth's radio communications take the place

of wires for connecting peripherals, telephones and computers.

WORDLIST:

Continuous sine wave -незатухающая (синусоидная) волна

amplitude modulated (AM) -амплитудная модуляция

frequency modulated (FM) -частотная модуляция

peak-to-peak voltage - размах напряжения (сигнала)

pulse modulation (PM) -импульсная модуляция

radio-controlled clock -радиоуправляемые часы

Global Positioning system (GPS) глобальная система навигации и определения положения;глобальная система позитионирования

transmitter -передатчик

receiver -приёмник

transceiver -приемопередатчик,

приёмопередающая станция

radio station; radio set; radio -радио станция

amplifier -усилитель

resonator -резонатор

generator -генератор (источник колебаний)

capacitor -конденсатор

inductor -индуктор

oscillator -гетеродин; колебательный контур

information signal -модулированный сигнал

transsducer - преобразователь

speakers -громкоговоритель; динамик,

fadphone -головной телефон; наушник

transtor -транзистор, кристаллический триод;

(разг.) радиоприёмник

to propagate through space - распространяться в пространстве

ham radio -радиолюбительское радио

EXPRESSIONS:

The receiver receives the radio waves and decodes the message from the sine wave it receives.— Приемник принимает волны радио частоты (радиоволны) и декодирует информацию, полученную с их помощью.

p icture part of a TV signal— видимая часть телесигнала

Bluetooth is a standard that works at two levels — Блютусс — стандарт связи, обеспечивающий связь на двух уровнях,

It provides agreement at the next level up — обеспечение согласования (связи) на более высоком уровне.

EXERCCISES:

I. Give equivalents to the following words and word combinations:

Radio set, приемопередающая станция, transmitter, приёмник, frequency modulated signal, наводить магнитное поле, information signal, rod antenna, чувствительный амперметр, induce electromagnetic fields, со скоростью света, optimalantenna size, конденсатор, radio communications, радио телефон, amplifier, radio controlled model, AM radio station.

II. Translate and answer the following questions:

a) What is a radio station?

b) Can you explain the principle difference between a continuous wave and radio

frequency wave?

c) What is the task of the modulator in a radio set?

d) Do you use a tuner when you operate your radio receiver? And what is its function?

e) Is the inductor together with the capacitor makes up the tuner?

f) What is the role of an amplifier in the two-way radio?

g) Is it possible to maintain the communication in between AM and FM radio stations?

III. Translate the following text:

Radio waves» transmit music, conversations, pictures and data invisibly through

the air, often over millions of miles — it happens every day in thousands of different ways! Even though radio waves are invisible and completely undetectable to humans, they have totally changed society. Whether we are talking about a cell phone, a baby monitor, a cordless phone or any one of the thousands of other wireless technologies, all of them use radio waves to communicate.

Here are just a few of the everyday technologies that depend on radio waves:

AM and FM radio broadcasts

Cordless phones

Garage door openers

Wireless networks

Radio-controlled toys

Television broadcasts

Cell phones

GPS receivers

Ham radios

Satellite communications

Police radios

Wireless clocks

The list goes on and on... Even things like radar and microwave ovens depend on |radio waves. Things like communication and navigation satellites would be impossible without radio waves, as would modern aviation — an airplane depends on a dozen different radio systems. The current trend toward wireless Internet access uses radio as well, and that means a lot more convenience in the future!

The funny thing is that, at its core, radio is an incredibly simple technology. With just a couple of electronic components that cost at most a dollar or two, you саn build simple radio transmitters and receivers.

IIV. Translate the text and be ready to discuss the general radio design:

Radio equipment.

A typical radio (rdo) station has the following basic components: transmitter (xmit-ter), receiver (rcvr), antenna (telescopic rod antenna) (ant), power supply unit (dry bat­tery or a generator) microphone (mic) and earphones or speaker.

The xmitter contains an oscillation generator for converting elec power into oscilla­tions of a predetermined radio frequency (rf) called the carrier frequency (freq), ampli­fiers for increasing the intensity of these oscillations, and a transducer for converting the information to be transmitted into a varying elec voltage proportional to each successive instantaneous intensity. For sound xmission a mic is the transducer. Other important components of the rdo xmitter are the modulator, which uses these proportionate volt­ages to control the variations in the oscillation intensity or the instantaneous freq of the carrier, and the antenna. The xmitting antenna is a conductor which radiates a similarly taodulated carrier wave when a RF AC is passed through it.

The signal may be impressed on the carrier wave either by FM or AM.

The essential components of a rdo rcvr are an antenna for receiving the electromagnetic waves and converting them into elec oscillations, amplifiers for increasing the intensity of these oscillations, detection equipment for demodulating, i. e. removing the voice information contained on the signals and converting it into a usable form, a speaker for converting the impulses into sound waves audible by the human. If detection equipment is sensitive to amplitude changes, it is called a detector. Equipment sensitive to freq changes is called a discriminator.

The incoming signal from the antenna is generally very weak. The sensitivity of modern rdo rcrs is so great that this signal can be detected and amplified to produce an intelligible sound from the speaker or headphones.

V. Translate into English the following material:

Радиостанция — это аппаратура, предназначенная для осуществления связи. По способу наложения (модулирования) передаваемой информации на несущую радио волну радио станции подразделяются на станции с амплитудной и частотной модуляцией. По месту установки различают радиостанции переносные, стационарные и установленные на подвижных наземных и воздушных средствах.

Приемопередающая радиостанция представляет собой приемник и передат­чик, помещенные в один корпус и составляющие единое целое. Конкретная конс­трукция и компоновка каждой радиостанции зависит от ее предназначения. Не­смотря на это, принцип действия всех радиостанций одинаков.

Радиопередатчикпредназначен для получения модулированных электричес­ких колебаний в диапазонах радиочастот и их последующего излучения антенной. Основные узлы передатчика: генератор преобразует энергию постоянного или пе­ременного тока в энергию колебаний радиочастоты; усилители — увеличивают интенсивность этих колебаний (амплитуду, частоту, фазу и т. д.) в соответствие с передаваемым сигналом; преобразователь — для преобразования передаваемой информации в электрическое напряжение.

Радиоприёмник служит (вместе с антенной) для выделения сигналов нуж- ного источника излучения радиоволн, их усиления и демодуляции, т. е. выделения из сигналов переданной голосом информации и преобразования её в рабочую форму для воздействия на воспроизводящее устройство: громкоговоритель, головные телефоны, и др.

VI. Translate the following extract:

Microphone transmitte:

The microphone transmitter may be one of the ordinary carbon granule types. A microphone consist simply of an elastic diaphragm bearing against a mass of carbon granules enclosed in a suitable chamber, the carbon granules forming part of an electrical circuit. When the microphone is not being spoken into the diaphragm remains stationary and exerts a constant pressure upon the carbon granules, the resistance of which remains, therefore, constant. On the other hand, when the diaphragm is set vibrating,as sound reaching it, the pressure exerted by the diagram against the can changes, and this change of pressure causes the resistance of the carbon granules to increase or decrease in accordance with the displacement of the diaphragm from its position of rest.

When the microphone is not being spoken into, the alternator produces a high frequency current of constant amplitude, i. е., an undamped current: the amplitude of this current is adjusted to the maximum by adjusting the inductance so as to make the natural frequency of the circuit equal to the frequency of the alternator.

LESSON #3