aero dynamic.doc

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Aero Dynamic Wind Mill with Reverse Charge Protection

AERO DYNAMIC WIND MIL WITH REVERSE CHARGE

PROTECTION

1.1 BLOCK DIAGRAM

Fig: 1.1 Block Diagram

1

AT89S52

Power

Supply

Unit

16X2 LCD

AC ripple

neutralizer

Unidirectio

nal Current

Controller

Rechargea

ble Battery Inverter

Voltage

SamplerADC

Contras

tAero

dynamic

wind blade

arrangemen

t

Geared DC

motor

ON/ OFF

control

switch

AC 230V

Load


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2. EMBEDDED SYSTEMS

An embedded system is a system which is going to do a predefined specified task is theembedded system and is even defined as combination of both software and hardware. A general-

purpose definition of embedded systems is that they are devices used to control, monitor or assist

the operation of equipment, machinery or plant. "Embedded" reflects the fact that they are an

integral part of the system. At the other extreme a general-purpose computer may be used to control

the operation of a large complex processing plant, and its presence will be obvious.

All embedded systems are including computers or microprocessors. Some of these

computers are however very simple systems as compared with a personal computer.

The very simplest embedded systems are capable of performing only a single function or set

of functions to meet a single predetermined purpose. In more complex systems an application

program that enables the embedded system to be used for a particular purpose in a specific

application determines the functioning of the embedded system. The ability to have programs means

that the same embedded system can be used for a variety of different purposes. In some cases a

microprocessor may be designed in such a way that application software for a particular purpose can

be added to the basic software in a second process, after which it is not possible to make further

changes. The applications software on such processors is sometimes referred to as firmware.

The simplest devices consist of a single microprocessor (often called a "chip), which may itself be

packaged with other chips in a hybrid system or Application Specific Integrated Circuit (ASIC). Its input

comes from a detector or sensor and its output goes to a switch or activator which (for example) may start or

stop the operation of a machine or, by operating a valve, may control the flow of fuel to an engine.

As the embedded system is the combination of both software and hardware

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Figure: 2 Block diagram of Embedded System

Software deals with the languages like ALP, C, and VB etc., and Hardware deals with Processors,

Peripherals, and Memory.

Memory: It is used to store data or address.

Peripherals: These are the external devices connected

Processor: It is an IC which is used to perform some task

Applications of embedded systems

Manufacturing and process control

Construction industry

Transport

Buildings and premises

Domestic service

Communications

Office systems and mobile equipment

3

Embedded

System

Software Hardware

ALP

C

VB

Etc.,

Processor

Peripherals

memory


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Banking, finance and commercial

Medical diagnostics, monitoring and life support

Testing, monitoring and diagnostic systems

Processors are classified into four types like:

Micro Processor (p)

Micro controller (c)

Digital Signal Processor (DSP)

Application Specific Integrated Circuits (ASIC)

Micro Processor (p):

A siliconchipthat contains a CPU. In the world ofpersonal computers, the terms microprocessorand CPU are used interchangeably. At the heart of all personal computers and most workstations

sits a microprocessor. Microprocessors also control the logic of almost all digital devices, from

clock radios to fuel-injection systemsfor automobiles.

Three basic characteristics differentiate microprocessors:

Instruction set: The set of instructions that the microprocessor can execute.

Bandwidth : The number ofbits processed in a single instruction.

Clock speed : Given in megahertz (MHz), the clock speed determines how many instructions per

second theprocessorcan execute.

In both cases, the higher the value, the more powerful the CPU. For example, a 32-bit

microprocessor that runs at 50MHz is more powerful than a 16-bit microprocessor that runs at

25MHz. In addition to bandwidth and clock speed, microprocessors are classified as being either

RISC (reduced instruction set computer) orCISC (complex instruction set computer).

A microprocessor has three basic elements, as shown above. The ALU performs allarithmetic computations, such as addition, subtraction and logic operations (AND, OR, etc). It is

controlled by the Control Unit and receives its data from the Register Array. The Register Array is

a set of registers used for storing data. These registers can be accessed by the ALU very quickly.

Some registers have specific functions - we will deal with these later. The Control Unit controls

the entire process. It provides the timing and a control signal for getting data into and out of the4
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registers and the ALU and it synchronizes the execution of instructions (we will deal with

instruction execution at a later date).

Micro Controller (c):

A microcontroller is a small computer on a single integrated circuit containing a processor

core, memory, and programmable input/output peripherals. Program memory in the form ofNOR

flash orOTP ROM is also often included on chip, as well as a typically small amount of RAM.

Microcontrollers are designed for embedded applications, in contrast to the microprocessors used

in personal computers or other general purpose applications.

Figure: 2 Block Diagram of Micro Controller (c)

Digital Signal Processors (DSPs):

Digital Signal Processors is one which performs scientific and mathematical operation.

Digital Signal Processor chips - specialized microprocessors with architectures designed specifically

for the types of operations required in digital signal processing. Like a general-purpose

microprocessor, a DSP is a programmable device, with its own native instruction code. DSP chips

are capable of carrying out millions of floating point operations per second, and like their better-

known general-purpose cousins, faster and more powerful versions are continually being

introduced. DSPs can also be embedded within complex "system-on-chip" devices, often containing

both analog and digital circuitry.

5

Timer, Counter,

serial

communication

ROM, ADC, DAC,

Timers, USART,

Oscillators

Etc.,

ALU

CU

Memor

y
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Application Specific Integrated Circuit (ASIC):

ASIC is a combination of digital and analog circuits packed into an IC to achieve the desired

control/computation function

ASIC typically contains

CPU cores for computation and control

Peripherals to control timing critical functions

Memories to store data and program

Analog circuits to provide clocks and interface to the real world which is analog in nature

I/Os to connect to external components like LEDs, memories, monitors etc.

Computer Instruction Set

There are two different types of computer instruction set there are:

1. RISC (Reduced Instruction Set Computer) and

2. CISC (Complex Instruction Set computer)

Reduced Instruction Set Computer (RISC)

A RISC (reduced instruction set computer) is a microprocessor that is designed to perform a

smaller number of types of computer instruction so that it can operate at a higher speed (perform

more million instructions per second, or millions of instructions per second). Since each instruction

type that a computer must perform requires additional transistors and circuitry, a larger list or set of

computer instructions tends to make the microprocessor more complicated and slower in operation.

Besides performance improvement, some advantages of RISC and related design improvements are:

A new microprocessor can be developed and tested more quickly if one of its aims is to be less

complicated.

Operating system and application programmers who use the microprocessor's instructions will find

it easier to develop code with a smaller instruction set.

The simplicity of RISC allows more freedom to choose how to use the space on a microprocessor.

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Higher-level language compilers produce more efficient code than formerly because they have

always tended to use the smaller set of instructions to be found in a RISC computer.

RISC characteristics:

Simple instruction set:

In a RISC machine, the instruction set contains simple, basic instructions, from which more

complex instructions can be composed.

Same length instructions.

Each instruction is the same length, so that it may be fetched in a single operation.

1 machine-cycle instructions.

Most instructions complete in one machine cycle, which allows the processor to handle several

instructions at the same time. This pipelining is a key technique used to speed up RISC machines.

Complex Instruction Set Computer (CISC)

CISC, which stands for Complex Instruction Set Computer, is a philosophy for designing

chips that are easy to program and which make efficient use of memory. Each instruction in a CISC

instruction set might perform a series of operations inside the processor. This reduces the number of

instructions required to implement a given program, and allows the programmer to learn a small but

flexible set of instructions.

The advantages of CISC

At the time of their initial development, CISC machines used available technologies to

optimize computer performance.

Microprogramming is as easy as assembly language to implement, and much less expensive than

hardwiring a control unit.

The ease of micro-coding new instructions allowed designers to make CISC machines upwardly

compatible: a new computer could run the same programs as earlier computers because the new

computer would contain a superset of the instructions of the earlier computers.

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As each instruction became more capable, fewer instructions could be used to implement a given

task. This made more efficient use of the relatively slow main memory.

Because micro program instruction sets can be written to match the constructs of high-level

languages, the compiler does not have to be as complicated.

The disadvantages of CISC:

Still, designers soon realized that the CISC philosophy had its own problems, including:

Earlier generations of a processor family generally were contained as a subset in every new version

--- so instruction set & chip hardware become more complex with each generation of computers.

So that as many instructions as possible could be stored in memory with the least possible wasted

space, individual instructions could be of almost any length---this means that different instructions

will take different amounts of clock time to execute, slowing down the overall performance of the

machine.

Many specialized instructions aren't used frequently enough to justify their existence ---

approximately 20% of the available instructions are used in a typical program.

CISC instructions typically set the condition codes as a side effect of the instruction. Not only does

setting the condition codes take time, but programmers have to remember to examine the condition

code bits before a subsequent instruction changes them.

Memory Architecture

There two different types memory architectures there are:

Harvard Architecture

Von-Neumann Architecture

Harvard Architecture

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Computers have separate memory areas for program instructions and data. There are two or

more internal data buses, which allow simultaneous access to both instructions and data. The CPU

fetches program instructions on the program memory bus.

The Harvard architecture is a computer architecture with physically separate storage andsignal pathways for instructions and data. The term originated from the Harvard Mark I relay-based

computer, which stored instructions on punched tape(24 bits wide) and data in electro-mechanical

counters. These early machines had limited data storage, entirely contained within the central

processing unit, and provided no access to the instruction storage as data. Programs needed to be

loaded by an operator, the processor could notbootitself.

Figure: 2 Harvard Architecture

Modern uses of the Harvard architecture

The principal advantage of the pure Harvard architecture - simultaneous access to more than

one memory system - has been reduced by modified Harvard processors using modern CPU cache

systems. Relatively pure Harvard architecture machines are used mostly in applications where

tradeoffs, such as the cost and power savings from omitting caches, outweigh the programming

penalties from having distinct code and data address spaces.

Digital signal processors (DSPs) generally execute small, highly-optimized audio or video

processing algorithms. They avoid caches because their behavior must be extremely reproducible.

The difficulties of coping with multiple address spaces are of secondary concern to speed of

execution. As a result, some DSPs have multiple data memories in distinct address spaces to

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facilitate SIMD and VLIW processing. Texas Instruments TMS320 C55x processors, as one

example, have multiple parallel data busses (two write, three read) and one instruction bus.

Microcontrollers are characterized by having small amounts of program (flash memory) and data

(SRAM) memory, with no cache, and take advantage of the Harvard architecture to speed

processing by concurrent instruction and data access. The separate storage means the program and

data memories can have different bit depths, for example using 16-bit wide instructions and 8-bit

wide data. They also mean that instruction pre-fetch can be performed in parallel with other

activities. Examples include, the AVRby Atmel Corp, the PIC by Microchip Technology, Inc. and

the ARM Cortex-M3 processor (not all ARM chips have Harvard architecture).

Von-Neumann Architecture

A computer has a single, common memory space in which both program instructions and

data are stored. There is a single internal data bus that fetches both instructions and data. They

cannot be performed at the same time

The Von Neumann architecture is a design model for a stored-program digital computer

that uses a central processing unit (CPU) and a single separate storage structure ("memory") to hold

both instructions and data. It is named after the mathematician and early computer scientist John

von Neumann. Such computers implement a universal Turing machine and have a sequential

architecture.

A stored-programdigital computeris one that keeps its programmed instructions, as well

as its data, in read-write, random-access memory (RAM). Stored-program computers were

advancement over the program-controlled computers of the 1940s, such as the Colossus and the

ENIAC, which were programmed by setting switches and inserting patch leads to route data and to

control signals between various functional units. In the vast majority of modern computers, the

same memory is used for both data and program instructions. The mechanisms for transferring the

data and instructions between the CPU and memory are, however, considerably more complex thanthe original von Neumann architecture.

The terms "von Neumann architecture" and "stored-program computer" are generally used

interchangeably, and that usage is followed in this article.

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Figure: 2 Schematic of the Von-Neumann Architecture.

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Basic Difference between Harvard and Von-Neumann Architecture

The primary difference between Harvard architecture and the Von Neumann architecture is in the

Von Neumann architecture data and programs are stored in the same memory and managed by the

same information handling system.

Whereas the Harvard architecture stores data and programs in separate memory devices and they are

handled by different subsystems.

In a computer using the Von-Neumann architecture without cache; the central processing unit

(CPU) can either be reading and instruction or writing/reading data to/from the memory. Both of

these operations cannot occur simultaneously as the data and instructions use the same system bus.

In a computer using the Harvard architecture the CPU can both read an instruction and access data

memory at the same time without cache. This means that a computer with Harvard architecture can

potentially be faster for a given circuit complexity because data access and instruction fetches do

not contend for use of a single memory pathway.

Today, the vast majority of computers are designed and built using the Von Neumann architecture

template primarily because of the dynamic capabilities and efficiencies gained in designing,

implementing, operating one memory system as opposed to two. Von Neumann architecture may be

somewhat slower than the contrasting Harvard Architecture for certain specific tasks, but it is much

more flexible and allows for many concepts unavailable to Harvard architecture such as self

programming, word processing and so on.

Harvard architectures are typically only used in either specialized systems or for very specific uses.It is used in specialized digital signal processing (DSP), typically for video and audio processing

products. It is also used in many small microcontrollers used in electronics applications such as

Advanced RISK Machine (ARM) based products for many vendors.

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3. BLOCK DESCRIPTION

3.1 POWER SUPPLY:

The input to the circuit is applied from the regulated power supply. The a.c. input i.e., 230V fromthe mains supply is step down by the transformer to 12V and is fed to a rectifier. The output

obtained from the rectifier is a pulsating d.c voltage. So in order to get a pure d.c voltage, the output

voltage from the rectifier is fed to a filter to remove any a.c components present even after

rectification. Now, this voltage is given to a voltage regulator to obtain a pure constant dc voltage.

Fig 3.1: Power supply

Transformer:

13

RegulatorFILTER

HBridge

Rectifier

Step down

transformer

230V AC

50Hz D.COutput


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Usually, DC voltages are required to operate various electronic equipment and these

voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the a.c input

available at the mains supply i.e., 230V is to be brought down to the required voltage level. This is

done by a transformer. Thus, a step down transformer is employed to decrease the voltage to a

required level.

Fig 3.1: Transformer

Rectifier:

The output from the transformer is fed to the rectifier. It converts A.C. into pulsating D.C.

The rectifier may be a half wave or a full wave rectifier. In this project, a bridge rectifier is used

because of its merits like good stability and full wave rectification.

Fig 3.1: Rectifier

The Bridge rectifier is a circuit, which converts an ac voltage to dc voltage using both half

cycles of the input ac voltage. The Bridge rectifier circuit is shown in the figure. The circuit has four

diodes connected to form a bridge. The ac input voltage is applied to the diagonally opposite ends of

the bridge. The load resistance is connected between the other two ends of the bridge.

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For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct, whereas

diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series with the load

resistance RL and hence the load current flows through RL.

For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct whereas, D1

and D3 remain OFF. The conducting diodes D2 and D4 will be in series with the load resistance

RL and hence the current flows through RL in the same direction as in the previous half cycle. Thus a

bi-directional wave is converted into a unidirectional wave.

Fig: 3.1 Bridge rectifier

Filter:

Capacitive filter is used in this project. It removes the ripples from the output of rectifier and

smoothens the D.C. Output received from this filter is constant until the mains voltage and load is

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maintained constant. However, if either of the two is varied, D.C. voltage received at this point

changes. Therefore a regulator is applied at the output stage .

Fig: 3.1 Capacitor Filter

Voltage regulator:

As the name itself implies, it regulates the input applied to it. A voltage regulator is an

electrical regulator designed to automatically maintain a constant voltage level. In this project,

power supply of 5V and 12V are required. In order to obtain these voltage levels, 7805 and 7812

voltage regulators are to be used. The first number 78 represents positive supply and the numbers

05, 12 represent the required output voltage levels. The L78xx series of three-terminal positive

regulators is available in TO-220, TO-220FP, TO-3, D2PAK and DPAK packages and several fixedoutput voltages, making it useful in a wide range of applications. These regulators can provide local

on-card regulation, eliminating the distribution problems associated with single point regulation.

Each type employs internal current limiting, thermal shut-down and safe area protection, making it

essentially indestructible. If adequate heat sinking is provided, they can deliver over 1 A output

current. Although designed primarily as fixed voltage regulators, these devices can be used with

external components to obtain adjustable voltage and currents.

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Fig: 3.1 voltage regulator

3.2 AERO DYNAMIC WIND BLADE

Wind turbine blades are shaped to generate the maximum power from the wind at the

minimum cost. Primarily the design is driven by the aerodynamic requirements, but economics

mean that the blade shape is a compromise to keep the cost of construction reasonable. In

particular, the blade tends to be thicker than the aerodynamic optimum close to the root, where the

stresses due to bending are greatest. The blade design process starts with a best guess compromisebetween aerodynamic and structural efficiency. The choice of materials and manufacturing process

will also have an influence on how thin (hence aerodynamically ideal) the blade can be built. For

instance, prepreg carbon fibre is stiffer and stronger than infused glass fibre. The chosen

aerodynamic shape gives rise to loads, which are fed into the structural design. Problems identified

at this stage can then be used to modify the shape if necessary and recalculate the aerodynamic

performance.

Fig: 3.2 Aero Wind Blade

The Wind:

It might seem obvious, but an understanding of the wind is fundamental to windturbine design. The power available from the wind varies as the cube of the wind speed, so twice

the wind speed means eight times the power. This is why sites have to be selected carefully: below

about 5m/s (0mph) wind speed there is not sufficient power in the wind to be useful. Conversely,

strong gusts provide extremely high levels of power, but it is not economically viable to build

machines to be able to make the most of the power peaks as their capacity would be wasted most of17


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the time. So the ideal is a site with steady winds and a machine that is able to make the most of the

lighter winds whilst surviving the strongest gusts.

As well as varying day-to-day, the wind varies every second due to turbulence caused

by land features, thermals and weather. It also blows more strongly higher above the ground thancloser to it, due to surface friction. All these effects lead to varying loads on the blades of a turbine

as they rotate, and mean that the aerodynamic and structural design needs to cope with conditions

that are rarely optimal. By extracting power, the turbine itself has an effect on the wind: downwind

of the turbine the air moves more slowly than upwind.

The wind starts to slow down even before it reaches the blades, reducing the wind

speed through the disc (the imaginary circle formed by the blade tips, also called the swept area)

and hence reducing the available power. Some of the wind that was heading for the disc divertsaround the slower-moving air and misses the blades entirely. So there is an optimum amount of

power to extract from a given disc diameter: try to take too much and the wind will slow down too

much, reducing the available power. In fact the ideal is to reduce the wind speed by about two

thirds downwind of the turbine, though even then the wind just before the turbine will have lost

about a third of its speed. This allows a theoretical maximum of 59% of the winds power to be

captured (this is called Betzs limit). In practice only 40-50% is achieved by current designs.

Number of blades:

The limitation on the available power in the wind means that the more blades there are

the less power each can extract. A consequence of this is that each blade must also be narrower to

maintain aerodynamic efficiency. The total blade area as a fraction of the total swept disc area is

called the solidity, and aerodynamically there is an optimum solidity for a given tip speed; the

higher the number of blades, the narrower each one must be. In practice the optimum solidity is low

(only a few percent) which means that even with only three blades, each one must be very narrow.

To slip through the air easily the blades must be thin relative to their width, so the limited solidity

also limits the thickness of the blades. Furthermore, it becomes difficult to build the blades strong

enough if they are too thin or the cost per blade increases significantly as more expensive materials

are required. For this reason, most large machines do not have more than three blades. The other

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factor influencing the number of blades is aesthetics: it is generally accepted that three-bladed

turbines are less visually disturbing than one- or two-bladed designs.

How blades capture wind power:

Just like an aeroplane wing, wind turbine blades work by generating lift due to their

shape. The more curved side generates low air pressures while high pressure air pushes on the other

side of the aerofoil. The net result is a lift force perpendicular to the direction of flow of the air.

The lift force increases as the blade is turned to present itself at a greater angle to the

wind. This is called the angle of attack. At very large angles of attack the blade stalls and the lift

decreases again. So there is an optimum angle of attack to generate the maximum l if .Lift & drag

vectors. There is, unfortunately, also a retarding force on the blade: the drag. This is the force

parallel to the wind flow, and also increases with angle of attack. If the aerofoil shape is good, the

lift force is much bigger than the drag, but at very high angles of attack, especially when the blade

stalls, the drag increases dramatically. So at an angle slightly less than the maximum lift angle, the

blade reaches its maximum lift/drag ratio. The best operating point will be between these two

angles. Since the drag is in the downwind direction, it may seem that it wouldnt matter for a wind

turbine as the drag would be parallel to the turbine axis, so wouldnt slow the rotor down. It would

just create thrust, the force that acts parallel to the turbine axis hence has no tendency to speed up

or slow down the rotor. When the rotor is stationary (e.g. just before start-up), this is indeed the

case. However the blades own movement through the air means that, as far as the blade is

concerned, the wind is blowing from a different angle. This is called apparent wind. The apparent

wind is stronger than the true wind but its angle is less it rotates the angles of the lift and drag to

reduce the effect of lift force pulling the blade round and increase the effect of drag slowing it

down. It also means that the lift force contributes to the thrust on the rotor. The result of this is that,

to maintain a good angle of attack, the blade must be turned further from the true wind angle.

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Fig: 3.2 Angle of attack of wind

Fig: 3.2 angle of wind blow

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Fig: 3.2 contact of wind on wind mill

Apparent wind angles

The closer to the tip of the blade you get, the faster the blade is moving through the air

and so the greater the apparent wind angle is. Thus the blade needs to be turned further at the tips

than at the root, in other words it must be built with a twist along its length. Typically the twist is

around 0-20 from root to tip. The requirement to twist the blade has implications on the ease of

manufacture.

Blade section shape

Apart from the twist, wind turbine blades have similar requirements to aeroplane wings,

so their cross-sections are usually based on a similar family of shapes. In general the best lift/drag

characteristics are obtained by an aerofoil that is fairly thin: its thickness might be only 0-5% of its

chord length (the length across the blade, in the direction of the wind flow).

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Blade twist:

If there were no structural requirements, this is how a wind turbine blade would be

proportioned, but of course the blade needs to support the lift, drag and gravitational forces acting

on it. These structural requirements generally mean the aerofoil needs to be thicker than the

aerodynamic optimum, especially at locations towards the root (where the blade attaches to the hub)

where the bending forces are greatest. Fortunately that is also where the apparent wind is moving

more slowly and the blade has the least leverage over the hub, so some aerodynamic inefficiency at

that point is less serious than it would be closer to the tip. Having said this, the section cant get too

thick for its chord length or the air flow will separate from the back of the blade similar to what

happens when it stalls and the drag will increase dramatically.

Fig: 3.2 Blade Twist on Wind Mill

To increase thickness near the root without creating a very short, fat, aerofoil section,

some designs use a flat back section. This is either a standard section thickened up to a square

trailing (back) edge, or a longer aerofoil shape that has been truncated. This reduces the drag

compared to a rounder section, but can generate more noise so its suitability depends on the wind

farm site. There is a trade-off to be made between aerodynamic efficiency and structural efficiency

even if a thin blade can be made strong and stiff enough by using lots of reinforcement inside, it

might still be better to make the blade a bit thicker (hence less aerodynamically efficient) if it saves

so much cost of material that the overall cost of electricity is reduced. The wind is free after all; its

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only the machine that we have to pay for. So there is inevitably some iteration in the design process

to find the optimum thickness for the blade.

Blade platform shape:

The platform shape is chosen to give the blade an approximately constant slowing effect

on the wind over the whole rotor disc (i.e. the tip slows the wind to the same degree as the centre or

root of the blade). This ensures that none of the air leaves the turbine too slowly (causing

turbulence), yet none is allowed to pass through too fast (which would represent wasted energy).

Remembering Betzs limit discussed above, this results in the maximum power extraction.

Because the tip of the blade is moving faster than the root, it passes through more volume of air,

hence must generate a greater lift force to slow that air down enough. Fortunately, lift increases

with the square of speed so its greater speed more than allows for that. In reality the blade can be

narrower close to the tip than near the root and still generate enough lift. The optimum tapering of

the blade platforms as it goes outboard can be calculated; roughly speaking the chord should be

inverse to the radius. So if the chord was 2m at 10m radius, it should be 10m at 1m radius. This

relationship breaks down close to the root and tip, where the optimum shape changes to account for

tip losses. In reality a fairly linear taper is sufficiently close to the optimum for most designs,

structurally superior and easier to build than the optimum shape.

Fig: 3.2 Plane Shape of Blade

Rotational speed:

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The speed at which the turbine rotates is a fundamental choice in the design, and is

defined in terms of the speed of the blade tips relative to the free wind speed (i.e. Before the wind

is slowed down by the turbine). This is called the tip speed ratio. High tip speed ratio means the

aerodynamic force on the blades (due to lift and drag) is almost parallel to the rotor axis, so relies on

a good lift/drag ratio. The lift/drag ratio can be affected severely by dirt or roughness on the blades.

Low tip speed ratio would seem like a better choice but unfortunately results in lower aerodynamic

efficiency, due to two effects. Because the lift force on the blades generates torque, it has an equal

but opposite effect on the wind, tending to push it around tangentially in the other direction. The

result is that the air downwind of the turbine has swirl, i.e. it spins in the opposite direction to the

blades. That swirl represents lost power so reduces the available power that can be extracted from

the wind. Lower rotational speed requires higher torque for the same power output, so lower tip

speed results in higher wake swirl losses.

Fig: 3.2 Rotational Speed

The other reduction in efficiency at low tip speed ratio comes from tip losses, where high-

pressure air from the upwind side of the blade escapes around the blade tip to the low pressure side,

thereby wasting energy. Since power = force x speed, at slower rotational speed the blades need to

generate more lift force to achieve the same power. To generate more lift for a given length the

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blade has to be wider, which means that, geometrically speaking, a greater proportion of the blades

length can be considered to be close to the tip. Thus more of the air contributes to tip losses and the

efficiency decreases. Various techniques can be used to limit tip losses such as winglets (commonly

seen on airliners) but few are employed in practice owing to their additional cost. The higher lift

force on a wider blade also translates to higher loads on the other components such as the hub and

bearings, so low tip speed ratio will increase the cost of these items. On the other hand the wide

blade is better able to carry the lift force (as discussed previously), so the blade itself may be

cheaper. All this means that turbine designers typically compromise on tip speed ratios in the

region of -0, so at design wind speed (usually 2-5 meters per second) the blade tip can be moving at

around 20 m/s (approximately 20 miles per hour). There are practical limits on the absolute tip

speed too: at these speeds, bird impacts and rain erosion start to become a problem for the longevity

of the blades and noise increases dramatically with tip speed.

Power and pitch control

For an economical design, the maximum performance of the generator and gearbox need

to be limited to an appropriate level for the turbines operating environment. The ideal situation is

for the turbine to be able to extract as much power as possible from the wind up to the rated power

of the generator, then limit the power extraction at that level as the wind increases further. Turbine

Power Curve WE Handbook- 2- Aerodynamics and Loads 9 If the blades angle is kept constant, theturbine is unable to respond to changes in wind speed. Not only does this make it impossible to

maintain an optimum angle of attack to generate the maximum power at varying wind speeds, the

only way to depower the machine in high wind speeds is by relying on the blades to stall (known

as passive stall control). This doesnt give the perfectly flat power curve above the rated wind

speed shown in the graph above, so to limit the maximum power, a passive stall-controlled turbine

will usually be operating somewhat below its maximum potential. If instead the blades are attached

via a bearing that allows the angle of attack to be varied (active pitch control), the blades can be

angled to maintain optimum efficiency right up to the design wind speed (at which the generator is

producing itsratedoutput). Above that wind speed they can be feathered, i.e. rotated in pitch to

decrease their angle of attack and hence their lift, so controlling the power. In survival conditions,

the turbine can be stopped altogether and the blades feathered to produce no turning force at all.

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An alternative to decreasing the angle of attack above the design wind speed is deliberately

to increase it to the point where the blade stalls (active stall control). This decreases lift and

increases drag, so has the desired slowing effect on blade rotation. It is also less sensitive to gusts

of wind than feathering: by decreasing the apparent wind angle, gusts increase the angle of attack so

tend to make the blade stall more. Therefore controlling blade speed by stall rather than feathering

can be beneficial in gusty conditions. Both methods are used by different designs.

3.3 DC MOTOR:

In any electric motor, operation is based on simple electromagnetism. A current-

carrying conductor generates a magnetic field; when this is then placed in an external magnetic

field, it will experience a force proportional to the current in the conductor, and to the strength of

the external magnetic field. As you are well aware of from playing with magnets as a kid, opposite

(North and South) polarities attract, while like polarities (North and North, South and South) repel.

The internal configuration of a DC motor is designed to harness the magnetic interaction between

acurrent-carrying conductor and an external magnetic field to generate rotational motion.

Fig: 3.3 DC Motor

Let's start by looking at a simple 2-pole DC electric motor (here red represents a magnet or

winding with a "North" polarization, while green represents a magnet or winding with a "South"

polarization).

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Fig:3.3 Simple 2-pole dc electric motor

Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator, commutator,

field magnet(s), and brushes. In most common DC motors (and all that Beamers will see), the

external magnetic field is produced by high-strength permanent magnets1. The stator is the

stationary part of the motor -- this includes the motor casing, as well as two or more permanent

magnet pole pieces. The rotor (together with the axle and attached commutator) rotate with respect

to the stator. The rotor consists of windings (generally on a core), the windings being electrically

connected to the commutator. The above diagram shows a common motor layout -- with the rotor

inside the stator (field) magnets.

The geometry of the brushes, commutator contacts, and rotor windings are such that

when power is applied, the polarities of the energized winding and the stator magnet(s) are

misaligned, and the rotor will rotate until it is almost aligned with the stator's field magnets. As the

rotor reaches alignment, the brushes move to the next commutator contacts, and energize the next

winding. Given our example two-pole motor, the rotation reverses the direction ofcurrent through

the rotor winding, leading to a "flip" of the rotor's magnetic field, driving it to continue rotatin

Fig: 3.3 rotation of rotor in dc motor

In real life, though,DC motors will always have more than two poles (three is a very

common number). In particular, this avoids "dead spots" in the commutator. You can imagine how

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with our example two-pole motor, if the rotor is exactly at the middle of its rotation (perfectly

aligned with the field magnets); it will get "stuck" there. Meanwhile, with a two-pole motor, there is

a moment where the commutator shorts out the power supply (i.e., both brushes touch both

commutator contacts simultaneously). This would be bad for the power supply, waste energy, and

damage motor components as well. Yet another disadvantage of such a simple motor is that it would

exhibit a high amount oftorque "ripple" (the amount oftorqueit could produce is cyclic with the

position of the rotor).

So since most smallDCmotors are of a three-pole design, let's tinker with the workings of

one via an interactive animation (JavaScript required):

You'll notice a few things from this -- namely, one pole is fully energized at a time (but

two others are "partially" energized). As each brush transitions from one commutator contact to the

next, one coil's field will rapidly collapse, as the next coil's field will rapidly charge up (this occurs

within a few microsecond). We'll see more about the effects of this later, but in the meantime you

can see that this is a direct result of the coil windings' series wiring:

Fig: 3.3 Placing of Commutator in DC Motor

The use of an iron core armature (as in the Mabuchi, above) is quite common, and has a number of

advantages. First off, the iron core provides a strong, rigid support for the windings -- a particularly

important consideration for high-torque motors. The core also conducts heat away from the rotor

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windings, allowing the motor to be driven harder than might otherwise be the case. Iron core

construction is also relatively inexpensive compared with other construction types.

But iron core construction also has several disadvantages. The iron armature has a

relatively high inertia which limits motor acceleration. This construction also results in high

windinginductances which limit brush and commutator life.

In small motors, an alternative design is often used which features a 'coreless' armature

winding. This design depends upon the coil wire itself for structural integrity. As a result, the

armature is hollow, and the permanent magnet can be mounted inside the rotor coil.

Coreless DC motors have much lower armature inductance than iron-core motors of comparable

size, extending brush and commutator life/

Fig: 3.3 courtesy ofMicromole

The coreless design also allows manufacturers to build smaller motors; meanwhile, due

to the lack of iron in their rotors, coreless motors are somewhat prone to overheating. As a result,

this design is generally used just in small, low-power motors. Beamers will most often see

coreless DCmotors in the form of pager motors.

3.4 RIPPLE NUTRALIZER:

The most common meaning of ripple in electrical science, is the small unwanted

residualperiodic variation of the direct current (dc) output of a power supply which has been

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derived from an alternating current (ac) source. This ripple is due to incomplete suppression of the

alternating waveform within the power supply.

As well as this time-varying phenomenon, there is a frequency domain ripple that

arises in some classes offilterand othersignal processing networks. In this case the periodic

variation is a variation in the insertion loss of the network against increasing frequency. The

variation may not be strictly linearly periodic. In this meaning also, ripple is usually to be

considered an unwanted effect, its existence being a compromise between the amount of ripple and

other design parameters.

TIME DOMINE RIPPLE:

Full-wave rectifier circuit with a reservoir capacitor on the output for the purpose of

smoothing ripple

Ripple factor () may be defined as the ratio of the root mean square (rms) value of the

ripple voltage to the absolute value of the dc component of the output voltage, usually expressed as

a percentage. However, ripple voltage is also commonly expressed as thepeak-to-peakvalue. This

is largely because peak-to-peak is both easier to measure on an oscilloscope and is simpler to

calculate theoretically. Filter circuits intended for the reduction of ripple are usually

called smoothing circuits.

Fig: 3.4 Time domine ripple

The simplest scenario in ac to dc conversion is a rectifierwithout any smoothing

circuitry at all. The ripple voltage is very large in this situation; the peak-to-peak ripple voltage is

equal to the peak ac voltage. A more common arrangement is to allow the rectifier to work into a

large smoothing capacitorwhich acts as a reservoir. After a peak in output voltage the capacitor (C)

supplies the current to the load (R) and continues to do so until the capacitor voltage has fallen to

the value of the now rising next half-cycle of rectified voltage. At that point the rectifiers turn on

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again and deliver current to the reservoir until peak voltage is again reached. If the time constant,

CR, is large in comparison to the period of the ac waveform, then a reasonable accurate

approximation can be made by assuming that the capacitor voltage falls linearly. A further useful

assumption can be made if the ripple is small compared to the dc voltage. In this case the phase

angle through which the rectifiers conduct will be small and it can be assumed that the capacitor is

discharging all the way from one peak to the next with little loss of accuracy

Fig: 3.4 Ripple wave form

Ripple voltage from a full-wave rectifier, before and after the application of a smoothing capacitor

With the above assumptions the peak-to-peak ripple voltage can be calculated as:

For a full-wave rectifier:

For a half-wave rectification:

Where

App. is the peak-to-peak ripple voltage

Iis the current in the circuit

fis the frequency of the ac power

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Cis the capacitance

For the rms value of the ripple voltage, the calculation is more involved as the shape of the ripple

waveform has a bearing on the result. Assuming a saw tooth waveform is a similar assumption to

the ones above and yields the result:

Where

is the ripple factor

R is the resistance of the load

Another approach to reducing ripple is to use a series choke. A choke has a filtering action and

consequently produces a smoother waveform with less high-orderharmonics. Against this, the dc

output is close to the average input voltage as opposed to the higher voltage with the reservoir

capacitor which is close to the peak input voltage. With suitable approximations, the ripple factor is

given by:

Where

is the angular frequency 2f

L is the inductance of the choke

More complex arrangements are possible; the filter can be an LC ladder rather than a simple choke

or the filter and the reservoir capacitor can both be used to gain the benefits of both. The most

commonly seen of these is a low-pass-filterconsisting of a reservoir capacitor followed by a

series choke followed by a further shunt capacitor. However, use of chokes is deprecated in

contemporary designs for economic reasons. A more common solution where good ripple rejection

is required is to use a reservoir capacitor to reduce the ripple to something manageable and then

pass through a voltage regulatorcircuit. The regulator circuit, as well as regulating the output, will

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incidentally filter out nearly all of the ripple as long as the minimum level of the ripple waveform

does not go below the voltage being regulated to.

The majority of power supplies are now switched mode. The filtering requirements

for such power supplies are much easier to meet due to the frequency of the ripple waveform being

very high. In traditional power supply designs the ripple frequency is either equal to (half-wave), or

twice (full-wave) the ac line frequency. With switched mode power supplies the ripple frequency is

not related to the line frequency, but is instead related to the frequency of the chopper circuit.

The ripple frequency and its harmonics are within the audio band and will therefore be

audible on equipment such as radio receivers, equipment for playing recordings and

professional studio equipment.

The ripple frequency is within television video bandwidth. Analogue TV receivers will

exhibit a pattern of moving wavy lines if too much ripple is present.

The presence of ripple can reduce the resolution of electronic test and measurement

instruments. On an oscilloscope it will manifest itself as a visible pattern on screen.

Within digital circuits, it reduces the threshold, as does any form of supply rail noise, at

which logic circuits give incorrect outputs and data is corrupted.

High amplitude ripple currents reduce the life ofelectrolytic capacitors.

Fig:3.4 Ripple on a fifth order prototype Chebyshev filter

Ripple in the context of the frequency domain is referring to the periodic variation

in insertion loss with frequency of a filter or some othertwo-port network. Not all filters exhibit

ripple, some have monotonically increasing insertion loss with frequency such as the Butterworth

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filter. Common classes of filter which exhibit ripple are the Chebyshev filter, inverse Chebyshev

filterand the Elliptical filter. The ripple is not usually strictly linearly periodic as can be seen from

the example plot. Other examples of networks exhibiting ripple are impedance matching networks

that have been designed using Chebyshev polynomials. The ripple of these networks, unlike regular

filters, will never reach 0dB at minimum loss if designed for optimum transmission across the pass

band as a whole.

The amount of ripple can be traded for other parameters in the filter design. For instance, the rate

ofroll-offfrom thepass band to the stop band can be increased at the expense of increasing the

ripple without increasing the order of the filter (that is, the number of components has stayed the

same). On the other hand, the ripple can be reduced by increasing the order of the filter while at the

same time maintaining the same rate of roll-off.

3.5RECHARGEBLE BATTERIES

A rechargeable battery or storage battery is a group of one or more electrochemical

cells. They are known as secondary cells because their electrochemical reactions are electrically

reversible. Rechargeable batteries come in many different shapes and sizes, ranging anything froma button cell to megawatt systems connected to stabilize an electrical distribution network. Several

different combinations of chemicals are commonly used, including: lead-acid, nickel

cadmium(NiCad), nickel metal hydride (Nigh), lithium ion (Li-ion), and lithium ion polymer(Li-ion

polymer).

Fig: 3.5 Rechargeable Batteries

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Rechargeable batteries have lower total cost of use and environmental impact than

disposable batteries. Some rechargeable battery types are available in the same sizes as disposable

types. Rechargeable batteries have higher initial cost, but can be recharged very cheaply and used

many times.

Rechargeable batteries are used forautomobile starters, portable consumer devices, light

vehicles (such as motorized wheelchairs, golf carts, electric bicycles, and electric forklifts), tools,

anduninterruptible power supplies. Emerging applications in hybrid electric vehicles and electric

vehiclesare driving the technology to reduce cost and weight and increase lifetime. Normally, new

rechargeable batteries have to be charged before use; newerlow self-discharge batteries hold their

charge for many months, and are supplied charged to about 70% of their rated capacity.

Grid energy storage applications use rechargeable batteries for load leveling, where

they store electric energy for use during peak load periods, and for renewable uses, such as storing

power generated fromphotovoltaic arrays during the day to be used at night. By charging batteries

during periods of low demand and returning energy to the grid during periods of high electrical

demand, load-leveling helps eliminate the need for expensivepeaking power plants and

helpsamortize the cost of generators over more hours of operation.

The USNational Electrical Manufacturers Association has estimated that U.S. demand

for rechargeable batteries is growing twice as fast as demand for non -rechargeable.

CHARGING AND DISCHARGING

During charging, the positive active material is oxidized, producing electrons, and the

negative material isreduced, consuming electrons. These electrons constitute thecurrent flow in the

external circuit. The electrolyte may serve as a simple buffer forion flow between the electrodes, as

inlithium-ion and nickel-cadmium cells, or it may be an active participant in

the electrochemical reaction, as inlead-acid cells.

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Fig: 3.5 charging of a secondary cell battery. Fig: 3.5 Battery charger

Fig: 3.5 A solar-powered charger for rechargeable batteries

The energy used to charge rechargeable batteries usually comes from abattery chargerusing

AC mains electricity. Chargers take from a few minutes (rapid chargers) to several hours to charge a

battery. Most batteries are capable of being charged far faster than simple battery chargers are

capable of; there are chargers that can charge consumer sizes of NiMH batteries in 15 minutes. Fast

charges must have multiple ways of detecting full charge (voltage, temperature, etc.) to stop

charging before onset of harmful overcharging.

Rechargeable multi-cell batteries are susceptible to cell damage due to reverse

charging if they are fully discharged. Fully integratedbattery chargers that optimize the charging

current are available.

Attempting to recharge non-rechargeable batteries with unsuitable equipment may

causebattery explosionFlow batteries, used for specialised applications, are recharged by replacing

the electrolyte liquid.

Battery manufacturers' technical notes often refer to VPC; this is volts percell, and

refers to the individual secondary cells that make up the battery. For example, to charge a 12 V

battery (containing 6 cells of 2 V each) at 2.3 VPC requires a voltage of 13.8 V across the battery's

terminals.

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Non-rechargeable alkaline and zinc-carbon cells output 1.5V when new, but this

voltage gradually drops with use. Most NiMH AA and AAA batteries rate their cells at 1.2 V, and

can usually be used in equipment designed to use alkaline batteries up to an end-point of 0.9 to 1.2V

Reverse charging:Subjecting a discharged cell to a current in the direction which tends to discharge it

further, rather than charge it, is called reverse charging; this damages cells. Reverse charging can

occur under a number of circumstances, the two most common being:

When a battery or cell is connected to a charging circuit the wrong way round.

When a battery made of several cells connected in series is deeply discharged.

When one cell completely discharges ahead of the rest, the live cells will apply a reverse current tothe discharged cell ("cell reversal"). This can happen even to a "weak" cell that is not fully

discharged. If the battery drain current is high enough, the weak cell's internal resistance can

experience a reverse voltage that is greater than the cell's remaining internal forward voltage. This

results in the reversal of the weak cell's polarity while the current is flowing through the cells. [3]

[4] this can significantly shorten the life of the affected cell and therefore of the battery. The higher

the discharge rate of the battery needs to be, the better matched the cells should be, both in kind of

cell and state of charge. In some extreme cases, the reversed cell can begin to emit smoke or catch

fire.

In critical applications using Ni-Cad batteries, such as in aircraft, each cell is individually

discharged by connecting a load clip across the terminals of each cell, thereby avoiding cell

reversal, then charging the cells in series.

3.6 INVERTER

An inverter is an electrical device that converts direct current (DC) to alternating

current (AC); the converted AC can be at any required voltage and frequency with the use of

appropriate transformers, switching, and control circuits. Solid-state inverters have no moving parts

and are used in a wide range of applications, from small switching power supplies in computers, to

large electric utilityhigh-voltage direct current applications that transport bulk power. Inverters are

commonly used to supply AC power from DC sources such as solar panels orbatteries.

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Fig: 3.6 Inverter

There are two main types of inverter. The output of a modified sine wave inverter is similar

to a square wave output except that the output goes to zero volts for a time before switching positive

or negative. It is simple and low cost (~$0.10USD/Watt) and is compatible with most electronic

devices, except for sensitive or specialized equipment, for example certain laser printers. A pure

sine wave inverter produces a nearly perfect sine wave output (


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Fig:3.6 Inverter snap

An inverter converts the DC electricity from sources such as batteries, solar panels,

orfuel cells to AC electricity. The electricity can be at any required voltage; in particular it can

operate AC equipment designed for mains operation, or rectified to produce DC at any desired

voltage. Grid tie inverterscan feed energy back into the distribution network because they produce

alternating current with the same wave shape and frequency as supplied by the distribution system.

They can also switch off automatically in the event of ablackout. Micro-inverters convert direct

current from individual solar panels into alternating current for the electric grid. They are grid tie

designs by default.

Uninterruptible power supplies:

Anuninterruptible power supply (UPS) uses batteries and an inverter to supply AC

power when main power is not available. When main power is restored, a rectifiersupplies DC

power to recharge the batteries.

Induction heating:

Inverters convert low frequency main AC power to higher frequency for use in induction

heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the

DC power to high frequency AC power.

HVDC power transmission:

With HVDC power transmission, AC power is rectified and high voltage DC power is

transmitted to another location. At the receiving location, an inverter in a static inverter

plant converts the power back to AC.

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Variable-frequency drive :

Avariable-frequency drive controls the operating speed of an AC motor by controlling

the frequency and voltage of the power supplied to the motor. An inverter provides the controlled

power. In most cases, the variable-frequency drive includes a rectifierso that DC power for theinverter can be provided from main AC power. Since an inverter is the key component, variable-

frequency drives are sometimes called inverter drives or just inverters.

Electric vehicle drives:

Adjustable speed motor control inverters are currently used to power the traction

motors in someelectric and diesel-electric rail vehicles as well as somebattery electric

vehiclesand electric highway vehicles such as theToyota Pries and Frisker Karma. Various

improvements in inverter technology are being developed specifically for electric vehicle

applications.[2] In vehicles withregenerative braking, the inverter also takes power from the motor

(now acting as a generator) and stores it in the batteries.

Air conditioning :

An air conditionerbearing the inverter tag uses a variable-frequency drive to control the

speed of the motor and thus the compressor.

The general case:Atransformerallows AC power to be converted to any desired voltage, but at the same

frequency. Inverters, plus rectifiers for DC, can be designed to convert from any voltage, AC or DC,

to any other voltage, also AC or DC, at any desired frequency. The output power can never exceed

the input power, but efficiencies can be high, with a small proportion of the power dissipated as

waste heat.

Basic designs:

In one simple inverter circuit, DC power is connected to a transformerthrough the centre

tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow

back to the DC source following two alternate paths through one end of the primary winding and

then the other. The alternation of the direction of current in the primary winding of the transformer

produces alternating current (AC) in the secondary circuit.

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