microprocessor controlled ac and dc drives ppt

Presented By

Md Manzar Nezami Md Mustafa kamal

A microprocessor is an electronic device that consists of millions (or billions) of transistors packed into one IC.

Its function is to execute instructions in the form of programs, calculate and store its results.

Microprocessors are used widely in our everyday lives.

µP is a complex, powerful device:◦ Able to process huge amounts of data.◦ Built using transistors etched on silicon die.◦ Needs external components to support operation.

Microcomputer system – support µP operations.

The microprocessor can be used to perform complex operations by giving it instructions.

These instructions are called programs. Programs are loaded into memory, and are

executed line-by line by the microprocessor.

Definition: A complete electronic system built around the microprocessor to support the microprocessor operation.

May consist of CPU, memory, I/O (disk drives, keyboard, mouse), system bus, and supporting circuitry.

CPU as the “brain” – controls actions of all components.

ROM

Keyboard Mouse HDD

Floppy RAM

CD-ROMSupporting

CircuitryCPU

Keypad

Memory

Power Supply LCD DisplayCPU

A µP-based system consists of many components:◦ CPU.◦ Memory.◦ I/O: disk drives, keyboard, mouse.◦ System Bus.◦ Supporting circuitry.

All components communicate using System Bus.

Parallel I/O Serial I/OInterrupt

Circuit

Timing CPU Memory

System Bus

“Master” of all components. Job:

◦ Get instructions from memory.◦ Execute instructions.◦ Perform calculations (may use math co-

processor). ◦ Control bus operations.

CPU

CPU consists of:◦ ALU (Arithmetic/Logic Unit):

Performs arithmetic/ logic computations.◦ CU (Control Unit):

Responsible to retrieve instructions, analyze, then execute.

◦ Registers: Fast internal storage. Used to temporarily store addresses, data, processor

status.

Stores instructions and data for CPU. Each memory location given unique

address.◦ CPU refers to address to access.

Types: ◦ Read-Only Memory (ROM).◦ Random-Access Memory (RAM).◦ Non-Volatile Memory (NVM).

Memory

Synchronizes all components in the system.◦ All components refer to the clock timing for

operations. Generates square waves at constant

intervals. Crystal oscillator + timing circuitry. Higher clock speed allow computers to

function faster.

Timing

Input/Output. Connects µP with external devices:

◦ Add functionality to µP. Interfaces with µP using ports. Examples:

◦ Keyboard.◦ Mouse.◦ Display monitor.

Built into board

Using card slots.

An electric motor together with its control equipment and energy transmitting device forms an Electric Drives. Some examples of electric-drive systems are: A ceiling fan motor with regulator and also with blades, a food mixer with food to be processed, a motor and conveyer belt with material on its belt and so on.

Electric drives are mainly two types:- DC Drives AC drives

AC drives are those in which motive power provided by ac motors. Though speed control of dc motors is easy as compared to ac motors, but ac motors have some advantages which outweighed the advantages of dc motors, and so with the development of different techniques of speed control of ac motor drives, now days, ac motor drives are more extensively use in industries.

Low maintenance cost. AC drives have a better power factor in most

applications. Harmonics reduction is cheaper in case of AC

drives. Higher transient response capability. AC drives are of lower cost in comparison to

DC drives.

High braking cost. Complex braking strategy. Complex and expensive speed control

technique. Problem of switching losses. High insulation cost.

Two types of controlling

Hardwire control

Electronic control/digital control

Small size Fast response Less power consumption Accurate and efficient Controlling range increased System reliability is much more than

conventional one. economical

Control of 4-quadrant micro computer controlled dc drive system

Thyristor to be triggred

Current comparator

Four quadrant logic

Speed Comparator

Current control

Speed Control

Firing angle Evaluation

Line synchronizing circuit

Timer And logic

Pulse Ampli-fier

Motor Current

D A

D ASpeed Signal

Refrence speed Start/stop

Microcomputer

3-phase AC Supply

W

Fig. Schematic 4-Quadrant microcomputer controlled D.C. drive System

M

stopComma

nd?

stop

Changeover sequence

Torque reversal

?

Compute current error

Read motor current

Compute firing angle & output firing signal

Start comman

d?

start

Read reference speed

Calculate speed error & current reference

Initialization

Read motor speed

Stop sequence

noyes

yes

yes

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